College of Science and Technology
SUBMISSION CHECKLIST FOR MASTERS THESIS SUBMISSION: OCTOBER 2020
Project Title: HYDROPOWER POTENTIAL ASSESSMENT AND
MODELLING OF GRID INTERCONNECTION FOR THE NORTH-KIVU
PROVINCE IN THE DEMOCRATIC REPUBLIC OF CONGO (DRC)
Names of student: MUSHAGE BONDO Pascal
Student Number: 219014623
SN
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1
Comments raised by panel during research
proposal were fully addressed
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2
All UR postgraduate thesis writing guidelines
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Program of study: EPS
Names of approving supervisor and signature: Dr.-Ing. Getachew Biru
Date of approval : 12.10.2020
P.O. Box 4285 Kigali, Rwanda
Website: www.aceesd.ur.ac.rw
College of Science and Technology
HYDROPOWER POTENTIAL ASSESSMENT AND MODELLING
OF GRID INTERCONNECTION FOR THE NORTH-KIVU
PROVINCE IN THE DEMOCRATIC REPUBLIC OF CONGO
(DRC)
Thesis Number:
By
MUSHAGE BONDO Pascal
Registration Number: 219014623
A dissertation submitted to the African Center of Excellence in Energy for
Sustainable development
College of Science and Technology
University of Rwanda in partial fulfilment of the requirements for the
degree of
MASTERS OF ELECTRICAL POWER SYSTEMS
Adviser: Getachew Biru Worku (Dr. -Ing.)
Adama Science and Technology University
October 2020
1.
Declaration
I declare that this dissertation is the result of my work except where specifically
acknowledged, and it has been passed through the anti-plagiarism system and found to be
compliant and this is the approved final version of the thesis.
Student name and Number: MUSHEGE BONDO Pascal/ ID: 219014623
Signed:
Date:
Supervisor: Getachew Biru Worku (Dr. -Eng.)
Signed:
Date:
i
2.
Acknowledgements
My deepest gratitude goes to my adviser Dr.-Ing. Getachew Biru Worku for his continuous
and consistent support, feedback valuable advice and remarks that highly contributed to the
elaboration of this work.
I am very grateful to the teaching staff of the African Center of Excellence in Energy for
Sustainable Development, through the University of Rwanda, College of Science and
Technology (ACEESD-UR/CST), for the knowledge that I gained from their lectures, which
helped me to conduct the actual research.
I would like to thank the World bank through collaboration with the government of Rwanda
for their financial support that allowed me to live in Rwanda and conduct my studies during
the time required for my master's program.
I am grateful to Dr Eng. Bikorimana Jean-Marie Vianney for his consistent advice and for
encouraging me to apply to this Master's program at the ACEESD and for his assistance in
my adaptation in Rwanda.
I thank as well Msc. Mukundufite Fabien for his support and his collaboration that helped
me to follow my goals during my studies.
Last but not the least, I thank all family members, friends and all staff of the Catholic
University La Sapientia in the Democratic Republic of Congo for their consistent
encouragement that motivated me to undertake this Master's program.
MUSHAGE BONDO Pascal
ii
3.
Abstract
North Kivu is one of the twenty-six provinces of DRC, and it is composed of six
territories. Among these territories, only a small part of Nyiragongo territory and Goma town
are connected to the Eastern National Grid (SNEL). Others are still living without electricity
despite the abundant hydropower potential available in the province which remains
unexploited. Previous studies have identified rivers with potential hydropower potential in
the province, but no technical study is done on how this potential can be integrated and
exploited in a way that the Government and investors get sufficient concrete information and
interest in developing the resource for the benefit of the population, who are mainly still
living in dark. Besides, the electricity demand of the province was still not well known,
which would help to evaluate at which rate the hydropower potential can contribute to
covering the regional electricity demand. This thesis aims to assess all hydropower potential
from existing hydrological data and see at which rate it can contribute to the electricity
supply in the province and design a Grid-connected system for major hydropower plants.
The Atlas of renewable energy of DRC estimated a total of 359.07𝑀𝑊 of hydropower
potential in the province. Based on 2020 data and empirical analysis, the actual electricity
demand of the province has been estimated at around 831.4𝑀𝑊. It was found that this actual
demand can be covered at 43.2% by the total hydropower potential. Moreover, this study
proposes a Grid-connected system for the province, where a total of 11 small and medium
hydropower plants have been interconnected for higher power reliability and security of the
local electricity supply. The pre-feasibility study of the proposed system was studied in
RETSCreen Expert software. The economic indices such as a PBP of 4.05 years, an IRR of
28.74 %, a BCR of 4.08% and a LCOE of 0.08 USD/kWh proved that the proposed system
was economically feasible. A Simulink model of the proposed system was simulated to
verify how power is being shared between different buses. It has been found that a total of
5.99MW out of a total generated of 250.15MW were lost in the network. From there, the
conclusion and recommendations for the improvement of the proposed system before its
implementation have been formulated.
Keywords: Hydropower potential assessment, Grid-connected system, RETSCReen Expert
software, Matlab/Simulink
iii
4.
List of symbols and acronyms
ABC: Aerial Bundled Cables
AC: Alternating Current
ACEESD: African Centre of Excellence in Energy for Sustainable Development
ACSR: Aluminium Conductor Steel-Reinforced
AVR: Automatic voltage regulator
BATS: Busbar Automatic Transfer Switch
BCR: Benefit-Cost Ratio
CAPEX: Capital Expenditure
CST: College of Science and Technology
DC: Direct Current
DER: Distributed Energy Resources
DF: Demand Factor
DG: Distributed Generator
Dr.: Doctor
DRC: Democratic Republic of Congo
g: Gravity
GIS: Geographic Information System
H: Head
ICLD: International Commission on Large Dams
IEC: International Electrical Committee
IEEE: International Electrical and Electronics Engineering
Ing.: Engineer
IRENA: International Renewable Energy Agency
IRR: Internal Rate of Return
kW: Kilowatt
kWh: Kilowatt-Hour
LCOE: Levelized Cost Of Electricity
m: Meter
MCDM: Multi-Criteria Decision Making
MG: Microgrid
MHPP: Micro Hydropower Plant
MPPT: Maximum Power Point Tracking
MSc: Master of Science
iv
MW: Megawatt
NPV: Net Present Value
O&M: Operating and Maintenance costs
OPEX: operating and expenditure
P: Power
PBP: Payback Period
PID: Proportional Integral Derivative
POI: Point of interconnection
Q: Flow rate
SCADA: Supervisory Control And Data Acquisition
SHP: Small Hydropower Plant
SNEL: Société National d’Electricité
SOCODEE: Société Congolaise de Distribution de l’Eau et de l’Electricité
UNDP: United Nations Development Programme
UR: University of Rwanda
ρ: Water Density
𝐷𝑖𝑣𝐹 : Diversity Factor
u
̅ : the stream velocity
v
5.
Table of contents
Declaration .................................................................................................................... i
Acknowledgements ...................................................................................................... ii
Abstract ....................................................................................................................... iii
List of symbols and acronyms..................................................................................... iv
Table of contents ......................................................................................................... vi
List of Tables............................................................................................................... ix
List of Figures ............................................................................................................. xi
Chapter 1 INTRODUCTION ....................................................................................... 1
1.1 Statement of the problem .............................................................................................1
1.2 Motivation ....................................................................................................................2
1.3 Objectives .....................................................................................................................2
1.3.1 The main objectives ..............................................................................................2
1.3.2 Specific objectives.................................................................................................3
1.4 Hypothesis ....................................................................................................................3
1.5 Research methods.........................................................................................................3
1.5.1 Data collection.......................................................................................................3
1.5.2 Data Analysis ........................................................................................................3
1.5.3 Modelling and simulation tools .............................................................................3
1.6 Expected Output ...........................................................................................................4
1.7 Outline of the Thesis ....................................................................................................4
Chapter 2. THEORETICAL BACKGROUND AND LITERATURE REVIEW ....... 5
2.1 Theoretical Background ...............................................................................................5
2.1.1 General overview of hydropower..........................................................................5
2.1.2. Types of hydropower plants .................................................................................5
2.1.3. Components of a hydropower plant .....................................................................6
2.1.4. Assessing the resource for hydropower installations ...........................................9
2.1.5. Introduction on grid-connected systems ............................................................13
vi
2.1.6 The Cost of hydropower projects ........................................................................15
22. Current Research Literature Review ..........................................................................19
2.2.1. Literature review on hydropower .......................................................................19
2.2.2. Literature review on interconnected systems ....................................................20
Chapter 3. DATA COLLECTION AND ANALYSIS .............................................. 22
3.1 Collection of existing hydro data of rivers in North-Kivu province ..........................22
3.1.1 Hydropower potential assessment in BENI territory ..........................................23
3.1.2 Hydropower potential assessment in LUBERO territory ....................................28
3.1.3 Hydropower potential assessment in MASISI territory ......................................32
3.1.4 Hydropower potential assessment in RUTSHURU territory ..............................35
3.1.5 Hydropower potential assessment in WALIKALE territory ...............................38
3.1.6 Estimation of electricity demand in NYIRAGONGO territory ..........................41
3.1.7 Estimation of the electricity demand in GOMA town ........................................42
3.2 Summary of the hydropower capacity and electricity demand in the province .........45
3.3 Other available energy resources in North-Kivu province.........................................46
3.4 Forecast of the electric power demand in the province ..............................................47
Chapter 4. DESIGN AND SIMULATION ................................................................ 49
4.1. Design of a Hydropower Grid-connected system .....................................................50
4.1.1 Civil components.................................................................................................50
4.1.2 Mechanical components ......................................................................................58
4.1.3 Electrical design ..................................................................................................64
4.2 Pre-feasibility study and economic analysis of the system through RETScreen
Software ...........................................................................................................................74
4.3 Simulation of the system in MATLAB/SIMULINK .................................................76
4.3.1 Simulation process in MATLAB/Simulink.........................................................77
4.3.2 Results and discussion.............................................................................................81
Chapter 5. CONCLUSION AND RECOMMENDATIONS ..................................... 86
5.1 Conclusion..................................................................................................................86
vii
5.2 Recommendations ......................................................................................................87
References .................................................................................................................. 89
APPENDICES............................................................................................................ 94
Appendix 1: Types of valve .............................................................................................94
Appendix 2: Selection of the turbine and the corresponging components .......................95
viii
6.
List of Tables
Table 2-1: Penstock Material Characteristics [9] ...................................................................8
Table 2-2:Turbine Selection Criteria [9] ................................................................................8
Table 3-1: Different factors for a group of loads [34], [35] .................................................23
Table 3-2: Identified hydropower sites in BENI Territory ..................................................25
Table 3-3: Residential loads for standard households ..........................................................26
Table 3-4: Estimated power consumption for commercial loads .........................................26
Table 3-5: Industrial loads in BENI territory .......................................................................27
Table 3-6: Estimated municipal loads in BENI territory .....................................................28
Table 3-7: Identified hydropower sites in LUBERO Territory ............................................30
Table 3-8: Estimation of industrial loads in LUBERO territory ..........................................31
Table 3-9: Estimated municipal loads in LUBERO territory ...............................................32
Table 3-10. Identified hydropower sites in MASISI territory ..............................................33
Table 3-11: Estimated industrial loads in MASISI territory ................................................34
Table 3-12: Estimated municipal loads in MASISI territory ...............................................35
Table 3-13: Hydro potential sites in RUTSHURU territory ................................................35
Table 3-14: Estimated industrial loads in RUTSHURU territory ........................................37
Table 3-15: Estimated municipal load in RUTSHURU territory .........................................37
Table 3-16: Assessed hydropower potential sites in WALIKALE territory ........................39
Table 3-17: Estimated industrial loads in WALIKALE territory.........................................40
Table 3-18: Estimated municipal load in MASISI territory .................................................40
Table 3-19: Estimated industrial loads in NYIRAGONGO territory...................................41
Table 3-20:Estimated municipal loads in NYIRAGONGO territory ...................................42
Table 3-21: Estimated household loads in Goma town ........................................................43
Table 3-22: Estimated industrial loads in Goma town .........................................................44
Table 3-23: Estimated municipal loads in GOMA town ......................................................44
Table 3-24: Recapitulation of the total electricity demand in North-Kivu province ...........45
Table 3-25: Other energy resources in North Kivu province [1].........................................46
Table 3-26: Load forecast in North-Kivu province ..............................................................48
Table 4-1: Total assessed hydropower sites in North-Kivu province ..................................49
Table 4-2: Selected hydropower sites for Grid-Connected system ......................................50
Table 4-3: Selection of a type of dam [53]...........................................................................51
Table 4-4: Coefficient of friction depending on the Reynolds Number [58] .......................55
Table 4-5: Calculated losses in the pipeline .........................................................................56
ix
Table 4-6: Estimated rotational speed for Francis turbines..................................................59
Table 4-7: Pros and cons of using Synchronous and Induction Generators [70] ................65
Table 4-8: Recommended rated economical terminal voltages of the generators [70] ........67
Table 4-9: Voltage drop of multicore PVC insulated cables [57] ........................................68
Table 4-10: Economic analysis of selected sites ..................................................................75
Table 4-11: Voltage of the transmission lines ......................................................................80
Table 4-12: Summary of the load flow analysis...................................................................81
Table 4-13: Load flow analysis at generation buses ............................................................83
Table 4-14: Active and reactive power absorbed by PQ and Z type loads ..........................84
Table 4-15: Measurement of frequency at generation Buses ...............................................85
Table A-1: Types and characteristics of each type of Inlet Valve .......................................94
Table A-2: Choice of turbines and related components as per standard ..............................95
x
7.
List of Figures
Fig. 2-1: Basic components of a hydropower plant [11]. .......................................................7
Fig. 2-2: Basic method of measuring the flow rate of a stream [14]....................................10
Fig. 2-3:Illustration of the refine method I [14] ...................................................................11
Fig. 2-4: Refined method II [14] ..........................................................................................12
Fig. 2-5: Sophisticated method [14] .....................................................................................12
Fig. 2-6: Measurement of the flow rate Q using the weir [14] ............................................12
Fig. 2-7: Capital cost as a function of hydropower capacity and site head [8] ....................15
Fig. 3-1: Hydrological map of BENI territory [1] ...............................................................24
Fig. 3-2: Hydropower potential in LUBERO territory [1]...................................................29
Fig. 3-3: Hydropower potential assessed in MASISI territory [1] ......................................33
Fig. 3-4: Identified rivers in RUTSHURU territory .............................................................36
Fig. 3-5: Hydropower potential of rivers in WALIKALE territory .....................................38
Fig 4-1: Net head and energy losses vs internal penstock diameter .....................................57
Fig. 4-2: Typical Francis turbine performance: constant speed and full gate ......................60
Fig. 4-3: Efficiency curve for Francis turbine ......................................................................61
Fig. 4-4: Basic Governor Control System [67] ....................................................................62
Fig. 4-5: Single line diagram of the proposed system ..........................................................76
Fig. 4-6: Block diagram of the hydropower plant [25] ........................................................77
Fig. 4-7: Hydropower plant model .......................................................................................79
Fig. 4-8: Simulink diagram of the Grid-connected system ..................................................80
Fig. 4-9: Variation of the overall frequency of the system ..................................................85
xi
1. Chapter 1 INTRODUCTION
1.1 Statement of the problem
The Democratic Republic of Congo (DRC), is known as the largest African country
and the third in the world in terms of hydropower potential, evaluated at around
100,000 𝑀𝑊. 44% of this potential is concentrated in the river Inga, and the remaining is
spread all over its 26 provinces. As per the United Nations Development Programme’s
(UNDP) report [1], 890 hydropower sites have been identified across the country. This
constitutes a huge potential that can make each province an independent power producer
through mini and micro-hydropower plants. Unfortunately, this potential remains
unexploited. Therefore it is observed some major challenges in the country such as:
•
Low generation capacity of electricity, with the consequence of low electricity access
(evaluated at 19.1% in 2017),
•
Most of the population is still living without electricity, and some areas are not
electrified yet.
•
The country does not have a single national Power Grid; therefore, the reliability of
the electricity supply is not improved.
From the total generated power of 2750 𝑀𝑊 [2], 99.6% is coming from
hydropower and represents only 3% of the available hydropower potential. Many reports
such as [1], [3], [4] have indicated that each province has sufficient capacity to generate
electricity for the local population from the available hydropower resources, but no technical
study has been conducted for the feasible implementation of such a project. The last
administrative division of the country led to a total of 26 provinces. The North Kivu
province which constitutes this particular research area is among the provinces in the
country, with a low rate of access to electricity which is less than 5%. With a land surface
of 59 631 𝑘𝑚², only the town of Goma and a small part of Nyiragongo Territory are
connected to the national utility SNEL through a line of around 5 𝑀𝑊 coming from
interconnected RUZIZI I and II hydropower plants located in South Kivu province. The
power generated is not sufficient even to supply the town which is of around 2 𝑚𝑖𝑙𝑙𝑖𝑜𝑛
inhabitants. Apart from this line connecting Goma town, other areas of the province are still
struggling to get access to electricity through some private initiatives and Christian
community projects. Most of the population is still using charcoal from the wood to cook
their food, which has a high impact on the environment because of the devastation of Virunga
National Park. There are also some parts of the province where the population is obliged to
1
use diesel-fired generation and small solar systems to power their houses. However, this is
a big problem because of the high cost of fuel and the initial cost of solar equipment. The
province has a huge energy potential, including non-renewable and renewable resources
available in the six territories, but not exploited yet. Therefore, this thesis intends to assess
the potential of producing electricity through interconnected hydropower to ensure the
economic development of the province. This will help to promote private sector investment
in the energy sector of the province and will play a major role to increase electricity access
in DRC as a whole.
1.2 Motivation
Hydropower is nowadays the dominant renewable energy source which can facilitate
the integration of other renewable energy resources [3]. The motivation to undertake this
research is justified by the fact that improved information on the hydropower potential of
the North-Kivu province and its spatial localization can help concerned bodies guide the
deployment of hydropower plants [3]. Also, it is an important input to help explore and
implement future energy systems without more climate impacts. Thus it will create jobs for
the population and contribute to the development of the whole province.
1.3 Objectives
1.3.1 The main objectives
The primary objective of this study is to assess all hydropower resources available in
the North Kivu province to promote the development of hydropower plants. The second
objective is to design an interconnected network, where all these hydropower plants will be
interconnected to create a single Grid for the province, to enhance the reliability of power
supply at affordable cost and low transmission losses. This will help to increase the
electricity access of the province from the actual rate of 3.1% to 100% in the coming
years.
2
1.3.2 Specific objectives
This thesis includes the following specific objectives:
•
Collection and analysis of existing data on the hydropower potential of rivers
in the region
•
Estimation of the power needed in the province
•
Design and modelling of an interconnected system
•
Calculation of the marginal cost of the energy produced
1.4 Hypothesis
By conducting this work, the research will try to prove the hypothesis settled as follow:
•
The electricity demand of North Kivu province can be covered economically by
promoting hydropower plants in each of its territories.
•
The reliability of the electricity supply in the province can be enhanced by an
interconnected system of hydropower plants.
1.5 Research methods
1.5.1 Data collection
Some official websites and recent reports published by credible international
organizations such as the World Bank, IRENA, RETScreen, etc. will be consulted. Hydro
data will be collected from the Atlas of renewable energies of DRC, which was published in
2014 by the UNDP [1]. This Atlas contains hydro data for each province. It will provide
information about the geographical localization of the rivers, and the estimated electricity
capacity of the concerned rivers in MW.
1.5.2 Data Analysis
The analysis of collected data will be facilitated by the use of some mathematic
formulations to determine the hydropower capacity of rivers in the whole region, the actual
electricity demand and the forecasting of the electric power demand of the province. The
conclusion and the recommendations will be undertaken based on simulation studies.
1.5.3 Modelling and simulation tools
Overall modelling and simulation of the proposed system will be carried out using
Matlab/Simulink and RETSCreen Expert software. Firstly, Matlab/Simulink software will
be used for the dynamic modelling of the hydropower plant components. The Simulink
3
model will be built with different blocks from the Matlab library (Simscape / Electrical /
Specialized Power Systems / Fundamental Blocks / Machines). Secondly, RETSCreen
software will be used for the pre-feasibility study of the proposed system.
1.6 Expected Output
This thesis will propose a feasible grid-connected system of the region that will help
the development of hydropower projects for the benefit of the population and the economy. It
will be a good starting point for other researchers and government bodies who would like to
undertake similar studies in other provinces.
1.7 Outline of the Thesis
The thesis is organized as follows: Chapter 2 will present the theoretical background
and literature review; Chapter 3 will focus on the data collection and their analysis; Chapter
4 will discuss the design, simulation, and modelling of the interconnected grid system, and
at the end, Chapter 5 will summarize the conclusion and recommendations of the research.
4
2.
Chapter 2. THEORETICAL BACKGROUND AND
LITERATURE REVIEW
2.1 Theoretical Background
2.1.1 General overview of hydropower
Mankind has been interested in hydropower development since ancient times. This
technology is so far the most cost-effective and the most reliable renewable energy source,
with a long lifetime in the range of 30 to 80 years. The flexibility in the design of hydropower
plants makes them the most preferable for base-load and peak demands and their high
capacity factors. Practically, when diverted water passes through the hydraulic turbine
coupled to a generator (Synchronous or induction), the water-energy is converted into
electricity [5], [6]. The generated electricity depends upon the height (head) and the rate of
flow of water. These two factors can help to identify the physical location of a hydropower
station, and its size.
2.1.2. Types of hydropower plants
Hydropower plants are classified: by size (generating capacity), height (head) and
the type of operation involved in the electricity generation.
2.1.2.1. Classification of hydropower plants by size
This classification includes large hydropower plants (that supply many consumers
with electricity), and small and micro hydropower plants (that individuals operate for their
own energy needs or to sell power to utilities) [7]. As presented in [8] hydropower plants
can be: Large (Size ≤ 100𝑀𝑊 ), Medium (20𝑀𝑊 ≤ 𝑠𝑖𝑧𝑒 ≤ 100𝑀𝑊 ),Small (1𝑀𝑊 ≤
𝑠𝑖𝑧𝑒 ≤ 20𝑀𝑊 ),Mini (100𝑘𝑊 𝑡𝑜 1𝑀𝑊 ), Micro ( 5 𝑘𝑊 𝑡𝑜 100 𝑘𝑊) or Pico hydropower
plant (𝑓𝑒𝑤 ℎ𝑢𝑛𝑑𝑟𝑒𝑑 𝑤𝑎𝑡𝑡𝑠 𝑢𝑝 𝑡𝑜 5 𝑘𝑊).
2.1.2.2. Classification of hydropower plants by the head of the river
This classification depends on the water pressure that runs the turbine by falling
from a given head. This head can be a natural one or created artificially. Generally, the
artificial head is created by the construction of a dam. Based on the head of water,
hydropower plants can be divided into three groups: High-head development, Medium-head
development, and Low-head development. High-head developments (ℎ𝑒𝑎𝑑 > 300𝑚), can
be found in mountainous regions, and use high-speed turbines [6]. Medium-head
developments are typically fed by a large reservoir of water retained by dikes and a dam at
5
a head varying between 30 𝑚 and 300 𝑚. They operate with medium-speed turbines. Lowhead developments with heads under 30 𝑚, use low-speed turbines which often extract the
energy from flowing rivers, without the use of a reservoir [6].
2.1.2.3. Classification of the hydropower by the type of the scheme
Here, the classification includes [8]:
• Run-of-river schemes: They can operate with a little water storage capacity behind
the dam or without any storage by deriving electricity from the natural elevation drop
and the flow of a river.
• Storage hydropower units: they are strictly dependent on water storage contained in
a reservoir behind the dam to de-couple generation from hydro inflows.
• Pumped storage hydropower schemes: They use off-peak electricity to pump water
from a reservoir located after the tailrace to the top of the reservoir so that the pumped
storage plant can generate at peak times and provide grid stability and flexibility
services.
2.1.3. Components of a hydropower plant
The main components of a conventional hydropower plant, as displayed in Fig. 2.1,
are classified into three types: civil work components, electromechanical, and Grid
connection components. Civil work components include:
• Dam (or Weir): Most hydropower plants rely on a dam, which is a concrete diversion
structure used as storage by holding back water [8].
• Intake: The intake of a hydro scheme is a structure designed to permit and control the
required amount of water flow to a waterway without producing a negative impact on
the local environment and with minimum head loss [9], [10], [11].
• Settling basin: This helps to prevent solid materials that come with the flowing of
water, to enter the penstock pipe, thus preventing them to damage the turbine.
• Forebay tank or surge chamber: The forebay is a basin located just before the
entrance to the penstock and which forms the connection between the channel and the
penstock [9],[11],[12]. It helps to protect the turbine from being damaged by the surges
that come with the water pressure [8]. Depending on its size it can also serve as a
reservoir to store water to cope with water demand created by a sudden increase in
loading on the turbine [9],[10].
6
• Penstock: It is a pipe between the forebay and the turbine which conveys the diverted
under-pressure water to the turbine [9],[8]. Designers strive to choose appropriate
materials to reduce this water pressure when building a penstock. The criteria for
choosing penstock material are given in Table 2-1.
Fig. 2-1: Basic components of a hydropower plant [11].
H: represents the head of water in a dam.
Z: represents the head between upstream and downstream.
•
Outflow: It is composed of pipelines called tailraces, which carry the used water
from the turbine to the river downstream. The outflow system may also include
“spillways” which allow the water to bypass the generation system and be “spilt” in
times of flood or very high inflows and reservoir levels [8].
•
The powerhouse: It is a building (conventional or underground) where
electromechanical equipment is installed for better operation [8].
Electromechanical work components include essentially:
• Hydraulic turbine: It provides useful mechanical energy to the generator for
producing electrical energy. We have two types: impulse and reaction turbines.
Impulse turbines extract the energy from the momentum of the flowing water, as they
are opposed to the weight of the water [8]. Turbines that fall under this category are
Pelton (Commonly used with high heads), Turgo, and cross-flow turbines [9],[13].
7
Table 2-1: Penstock Material Characteristics [9]
Material type
Welded steel
Polyethene
PVC
Cast iton
Asbestos cement
Ductile Iron
Young’s modulus
of elasticity E
(N/m2 )
206
0.55
2.75
78.5
n/a
16.7
Coefficient of
linear expansion
α (mm/°C )
12
140
57
10
8.1
11
Ultimate tensile
strength (N/
m2 )
400
5
13
140
n/a
340
n*
0.012
0.009
0.009
0.014
0.011
0.013
Where n* is manning’s coefficient of the material used.
• The “reaction turbine” develops power from the combined action of pressure energy
and kinetic energy of the water head [9]. Turbines that fall under this category are
Kaplan, Propeller, and Francis turbines [9],[13]. However, Francis turbines are up to
now the most preferred because of their high efficiencies, and their wide range of
applications in terms of heads and flow rates. [8].
Table 2-2:Turbine Selection Criteria [9]
Classification
Impulse
Reaction
Turbine Name
Head (m)
Pelton
Turgo
Cross-flow
Kaplan & Propeller
Francis radial flow
Francis mixed flow
50-1 000
30-200
2-50
3-40
40-200
10-40
Flow
(m3)
0.2-3
2-5
0.01-2
3-20
1-20
0.7-10
A particular turbine is chosen depending on the flow rate, the head, its availability in the
market, and the cost of maintenance [9],[13]. The choice can be made based on the
parameters given in Table 2-2.
The Grid connection is composed of the following components:
• Generator: it generates an alternating current (AC) when its rotor turns due to the
rotation of the turbine’s blades. It can be a synchronous or induction (asynchronous)
generator. Synchronous generators are extensively used in large-scale power
generation [13]; Whereas asynchronous generators are preferred in small hydropower
schemes for their adaptation to variable speeds of operation, their constant frequency
and their low cost [9],[13].
• The transformer: it is used to step up or down the voltage for different applications.
8
• Transmission lines: They transport the generated electricity up to the load or the Grid
[8].
Depending on the hydropower capacity of a given river, more time and effort are spent on
the construction of the dam, head race, water intake, penstock, surge chamber, tailrace, and
powerhouse [8]. Therefore, during the assessment of the hydropower resource, it is required
to determine how much time and effort will be spent on this stage of construction.
2.1.4. Assessing the resource for hydropower installations
The first step in assessing hydropower resources is to identify the available stream,
which may be useful for hydropower development. Some approximations of data, with an
accuracy of about ±50%, are needed to estimate the power potential of the site [14]. If these
approximations prove promising hydro resources, then a detailed investigation will be
carried out for collecting information about the rainfall of the region, taken over several
years. The remaining parameters which are the flow rate 𝑄 of the stream, and the available
vertical head (height) 𝐻 can be derived accordingly using the equation below:
Power (P) = Flow Rate (Q) × Head(H) × Gravity(g) × Water Density(ρ) (2.1)
Where 𝑄 is in 𝑚/𝑠, 𝐻 in meters and 𝒈 is the gravitational constant, 9.81 𝑚/𝑠 and 𝜌 is the
density of water (𝜌 = 1,000𝑘𝑔/𝑚 or 1,0𝑘𝑔/𝑙𝑖𝑡𝑒𝑟). Therefore,
P = 1.0 x 9.81 x Q x H (kW)
(2.2)
The friction losses in the water conduits, the turbine itself, and its casing affect the
mechanical power output of the turbine which becomes less than the value calculated by the
preceding equation. By taking into consideration the efficiency 𝜂 of the turbine, the effective
power of a hydropower system can be calculated as:
P = η × g × Q × H (kW)
(2.3)
However, the efficiency 𝜂 of large hydraulic turbines is between 90 and 94 per cent,
whereas for the generator it is even higher, ranging from 97 to 99 per cent, depending on its
size.
9
2.1.4.1 Determination of the height H
For nearly vertical falls, trigonometric methods are suitable; whereas for more gently
sloping sites, the use of level and pole is straightforward [14]. The available net head (𝐻𝑛 )
which contributes to determine the power at the output of the turbine can be derived from
the equation below:
Hn = Ht − H f
(2.4)
Where 𝐻t is the total head, and 𝐻f is the head losses due to frictions in different conduits. It
is required to keep 𝐻f around 𝐻𝑡 /3 by paying more attention to the choice of materials and
the design of the different conduits [14].
2.1.4.2 How to measure the flow rate 𝑸 of a river
To ensure better operation of a hydropower plant throughout the year, the hydro
turbine has to operate at its maximum rating whenever it is needed. Therefore, the flow rate
data of a river over the year can help the designer choose a suitable turbine that can ensure
continuous operation throughout the variation of the seasons [14]. The Speed and the size of
the stream determine the type of method that has to be used to measure the flow rate 𝑄. The
existing methods are summarized as follow:
i. Basic method
This method is considered as an accurate one and suitable for small flows.
Fig. 2-2: Basic method of measuring the flow rate of a stream [14]
The flow rate is measured after stopping the water path by a dam, or after diverting the whole
stream into a containing volume (Fig. 2-2) [14]. Thus, the flow rate can be measured from
the volume using Equation (2.5).
Q = (Volume passing in time ∆t)/∆t
10
(2.5)
ii. The refined method I
̅ of the water flow, by assuming the flow speed equals zero
It defines the mean speed 𝒖
at the bottom of the stream (because of viscous friction). Thus, the mean speed will be
slightly less than the speed 𝒖 s on the top surface. For a rectangular cross-section, for
example, the flow rate can be calculated as follow (Fig. 2-3):
Flow rate Q = (mean speed u̅) × (cross − section area A)
(2.6)
Where u̅ ≈ 0.8us
(2.7)
From Eq. (2.7), 𝐮
̅ symbolizes the velocity of the river and 𝒖𝒔 represents the speed on the
top surface of the water. A simple technic to determine this speed is to measure the time
taken by a floating leaf to go a certain distance along the stream [14]. The best results of the
measurement are obtained at a uniform cross-section of the river and at the places where the
river is sensibly straight [14].
Fig. 2-3:Illustration of the refine method I [14]
From Fig. 2-3 and Eq. (2.8), it can be seen that the cross-sectional surface 𝑨 is evaluated by
integrating the depth measured at different places across the stream [14]:
A≈
1
1
1
1
y z + ( y2 − y1 )(z1 + z2 ) + (y3 − y2 )(z2 + z3 ) + (y4 − y3 )z3
2 1 1
2
2
2
(2.8)
iii. Refined method II
This method is useful on a fast-flowing stream because it avoids the need for accurate
timing in the calculation of the flow rate. The method consists of taking the time and the
horizontal distance taken by a float to rise after being released from a standard depth below
the water surface [14]. This can be illustrated in Fig. 2-4.
11
Fig. 2-4: Refined method II [14]
iv. Sophisticated method
This is the most accurate method for large streams and is used by professionals.
Essentially the forward speed 𝒖 is measured with a small flow meter at the points of a twodimensional grid extending across the stream [14]. The flow rate is then evaluated by
summation.
Flow rate Q = ∫ udA
(2.9)
Fig. 2-5: Sophisticated method [14]
v. Using a weir
Fig. 2-6: Measurement of the flow rate Q using the weir [14]
Generally, in order to facilitate the measurement of the flow rate throughout the year,
it is required to build a weir on the river [14]. Thus, the water passing through the notch of
the weir will determine the flow rate of the concerned river. The calibration of the weir with
its suitable notch has to be done following a laboratory model or other standards that can be
found in handbooks.
12
2.1.5. Introduction to grid-connected systems
The accompanying steady growth in the integration of renewable energy generators
and the deregulation of electricity markets has resulted in high levels of interest in distributed
generation not only for remote area power but also in stronger parts of the grid [15].
Considering this fact, contemporary power system research has been increasingly focused
on how best to integrate distributed energy resources such as renewable generation devices
into the larger electricity grid [16]. When distinct distributed resources are grouped into a
single generator or load which is connected to the wider electricity system (utility grid), this
is called a grid-connected system. When such loads and generators are located within close
geographical proximity of each other, such a system is often referred to as a Microgrid (MG)
[16]. A MG is a smaller entity that can intelligently control and coordinate distributed energy
resources (DER) with the support of intelligent controllers and other necessary architecture
[15]. It can operate independently in islanding mode to supply a remote area, or can be
connected to the main grid to constitute “a grid-connected system”. Distributed Generations
(DGs) are classified into two main technologies: Conventional DGs and nonconventional
DGs. Conventional DGs are those which involve rotating machines and can be directly
connected to the grid, in contrast to the nonconventional DGs that generate a DC voltage,
and thus can’t be connected directly to the grid without a power electronics interface [15].
2.1.5.1 Advantages of a grid-connected system
The grid-connected system offers many advantages such as:
• Exchange of peak loads between the interconnected power stations: If the load curve
of a power station shows a peak demand that is greater than the rated capacity of the
plant, then the excess load can be shared by other stations interconnected with it.
• With an interconnected system, older and less efficient plants, (plants that are
inadequate to operate alone to supply a certain load), can be used to carry eventual
peak loads of short durations that may happen in the power system.
• The interconnected system is economical because the most efficient stations are
scheduled to work continuously, while the less efficient plants intervene only for peak
hours.
• The diversity factor of the system increases because the system interconnects different
stations that have different load curves. Therefore, the effective capacity of the whole
system is increased.
• Reduces plant reserve capacity thereby increasing the efficiency of the system.
13
• The interconnected system increases the reliability of supply. If one station breaks
down, the continuity of supply will be maintained by other healthy stations.
The evolution of the grid-connected system has been aided by the development and
application of smart grid concepts which expect grids to be operated more dynamically,
securely, efficiently, and economically with greater flexibility. These characteristics can be
implemented by large hydropower plants in a grid-connected system in case of large
electricity demands. However, when it comes to supplying electricity to remote areas with
low electricity demand, off-grid or mini-grid systems are preferable. Thus, Small
hydropower plants can be chosen as suitable technologies for these areas. In the case of
isolated areas where the hydropower development does not aloud any water storage, the
interconnection of generation units is required to avoid the impact of seasonal flow variations
on the system. This ensures a continuous electricity supply during dry seasons.
2.1.5.2 The Challenges for grid-connected system
There are many challenges in the implementation of a grid-connected system. Among
them we can illustrate the following:
• Control of the interconnected system: Control in this context refers to the scheme
and apparatus for ensuring that, various parameters of the system lie within limits that
will guarantee the desired behaviour of the system, including the effects of the
microgrid upon the wider grid and the safety of personnel [16].
•
Planning and design of grid-connected systems: The interaction between different
DGs needs more data to be processed and leads to a huge power flow system.
Therefore, for optimal planning and design, computational intelligence techniques and
mathematical modelling are needed, but they are not easy to handle.
•
Integrating Renewables into the grid: The intermittent of some renewable energies
and their need for power inverters also complicates the planning and operation of the
microgrid.
The major motivation behind the grid-connected system is to gain from the advantages
brought by the integration of renewable resources. These advantages can be evaluated as
environmental, social, economic and technical [17].
14
2.1.6 The Cost of hydropower projects
The cost can be measured in different ways, and each way of accounting for the cost
of power generation brings insights [18]. Practically the assessment of the feasibility of a
hydropower project consists of estimating the capital cost, the cost for operating and
maintenance (OPEX or O&M), plus the energy yield and associated tariff (also called
Levelized Cost of Electricity). This estimation is derived from standards developed by the
International Renewable Energy Agency (IRENA) as it will be presented in the following
sections. The total cost of hydropower development includes the cost of civil works and
electromechanical components. Moreover, the long transmission lines contribute
significantly to this cost. In general, the cost of civil works is directly influenced by the
characteristics of the hydro site unlike the cost of electro-mechanical equipment [8].
Therefore, the cost per kW of given hydropower plants is usually determined according to
the site characteristics that determine the civil works [8].
2.1.6.1 Total capital costs of hydropower schemes
The total capital cost refers to all costs that contribute to power generation. It can be
calculated on a unit basis as shown in the equation below:
Unit Capital cost [$/kW]= (Equipment cost + Engineering + civil cost + Construction cost +
Process contingency) / generation capacity [kW]
(2.10)
From this equation, the total generating cost of electricity can be derived as follow:
Generating Cost of electricity= Capital cost + Operating and Maintenance cost (2.11)
Fig. 2-7: Capital cost as a function of hydropower capacity and site head [8]
15
Large hydropower projects require large civil works thus, they play a major role in
the total cost, unlike small-scale hydropower projects. There is significantly less variation in
the electro-mechanical costs. The total installed costs for large-scale hydropower projects
typically range from 𝑈𝑆𝐷 1000/𝑘𝑊 to around 𝑈𝑆𝐷 3500/𝑘𝑊 [8]. Small-scale
hydropower projects up to 50 𝑀𝑊 can achieve competitive installed costs of on average
𝑈𝑆𝐷1500/𝑘𝑊 [18] depending on the country’s economy, the resource available, and the
site specific aspects. Practically, if the hydro site possesses a high head, the cost per 𝑘𝑊
may be reduced as well. This is shown in Fig.2.7. In the case of head sizes above 25 to 30
meters, it can be seen that their economies of scale are modest.
2.1.6.2 Electro-mechanical equipment costs
The cost of electro-mechanical equipment is defined by the size of the hydropower
plant. In order to reduce the impact of the size on the cost of hydropower development, the
total capacity is achieved by combining two or more units of small capacities. This
contributes as well to the availability of the power system, since in case of a fault, or during
maintenance on one unit, others may continue supplying electricity to the load or the grid.
The cost of the electro-mechanical components for hydropower schemes can be expressed
by the formula below [8]:
COST(per kW) = αP β−1 H β1
(2.12)
Where: 𝑃 is the power in 𝑘𝑊 of the turbines; 𝐻 is the head in meters; 𝛼, 𝛽 and 𝛽1 are the
coefficients that depend on the geographical, space, or time field in which they are used [19].
This type of analytical approach is a useful first-order method to estimate the electromechanical equipment cost.
2.1.6.4 Operation and maintenance costs (O&M)
Since hydropower is a green energy resource, it does not require fuel to generate
electricity. Only cost related to maintenance, repairs and taxes contributes to these O&M
costs. The recent study carried out in [18] has shown that the average O&M cost is slightly
less than 2% of the total installed costs per year, with a variation of between 1% and 3%.
Larger projects have O&M costs below the 2% average, while smaller projects approach
3%, or are higher than the average O&M costs [18]. However, this percentage does not take
into account the refurbishment of penstocks, tailraces and the replacement of major electromechanical equipment. The fact that the replacement time for electro-mechanical equipment
is infrequent and maybe more than 30 years, whereas the lifetime for the refurbishment of
16
tail races and penstocks maybe 50 years or mor, constitutes a great asset for hydropower
operation.
2.1.6.5 Levelized cost of electricity from hydropower
The LCOE is the price of electricity required for a project where revenues would
equal costs, including making a return on the capital invested equal to the discount rate [18].
An electricity price above this would yield a greater return on capital, while a price below it
would yield a lower return on capital, or even a loss [18]. In other terms, it can be understood
as the marginal cost when the time value of money is not taken into consideration. The
determination of the LCOE is facilitated by estimating the total capital cost of the project;
its economic life; the O&M costs; and the capacity factor (47% of the total capital cost) [18].
Generally, the LCOE is calculated as follows:
LCOE =
I +Mt+Ft
(1+r)t
t
∑n
i=1
(2.13)
Et
(1+r)t
∑n
i=1
Where: 𝑳𝑪𝑶𝑬 = the averaged lifetime Levelized Cost of Electricity; 𝑰 t = investment
expenditures in the year 𝒕; 𝑴t= Operations and maintenance expenditures in the year 𝒕; 𝑭t=
Fuel expenditures in a year 𝒕 (For this case 𝑭t= 𝟎, since no fuel cost for a hydropower
system); 𝑬t=total generated electricity in a year 𝒕; 𝒓 = discount rate and n = economic life
of the system. According to the updated research presented in 2018, the global weightedaverage 𝐿𝐶𝑂𝐸 of hydropower is USD 0.047/kWh [18].
The numerator of Equation (2.13) gives the net present value costs (𝑁𝑃𝑉𝑐𝑜𝑠𝑡), whereas the
denominator gives the net present value of the electricity generation (𝑁𝑃𝑉𝑔𝑒𝑛). The
equation becomes:
LCOE ($⁄kW) =
NPVcost
NPVgen
(2.14)
The 𝑁𝑃𝑉𝑐𝑜𝑠𝑡 takes into account inflation and returns to compare the actual present value to
the future’s present value of money. A positive net present value will mean that the project
is worth pursuing, as it creates benefits for the investor.
17
2.1.6.6 Internal rate of return and the discounted payback period
To recoup initial capital investments, two more parameters need to be calculated:
The internal rate of return and the discounted payback period. On one hand, the internal rate
of return (IRR) on a given investment or project is the annualized effective compounded
return rate or rate of return that results in a zero net present value of all cash flows (positive
and negative) [20]. Generally, by comparing the same projects in the same category of risk,
the one with the highest IRR will be the most interesting to investors than the others. On the
other hand, the payback period (PBP) is the period that determines when the investor would
recoup his initial capital investments if he undertakes the proposed project. The investment
will be feasible if the payback period is shorter than the investment period. The payback
period is calculated by counting the number of years taken to recover the cash invested in a
project [21]. The benefit of a hydropower plant operation in a given period will be the
product of power production and the fixed price of the power, within the period in question.
2.1.6.7 Benefit-cost ratio
The benefit-cost ratio (BCR) is sometimes a simple way to evaluate the feasibility of
investment. BCR is a comparison between the benefit and costs of an investment. The
investment is feasible if BCR is equal to or higher than 1; on the other hand, it is not feasible
for a BCR value lower than one [21].
18
22. Current Research Literature Review
2.2.1. Literature review on hydropower
In ancient times, the energy from the waterfall was used to turn wheat into flour by
using waterwheels in the grinding stone [8]. The first hydroelectric development began in
1870 in Crag side, England [8]. Such hydropower plants had small capacities by today’s
standards but pioneered the development of the modern hydropower industry. Hydropower
technologies have been the centre of interest for many scholars to promote an efficient
electrical power supply, without greenhouse gas emissions into the environment. Different
approaches have been used to analyse hydropower projects for several objectives. Some
recent works related to hydropower project development are revised here. In [22], A
comprehensive quantification of global hydropower potential is presented, including gross,
technical, economic, and exploitable estimates [22]. This research has shown that
hydropower constitutes a major renewable resource that can contribute to the development
of the global world without any greenhouse gas emissions in the energy generation process.
A case study of the Potential Assessment of Small Hydropower in selected Areas of BenchMaji and Sheka Zones in South-Western Ethiopia is presented in [9]. The research indicated
that the potential range of the selected rivers varies from 3.68 𝑘𝑊 to 500 𝑘𝑊 . The
Levelized Cost of energy which varies between 0.082$/ kWh and 0.259 $/ kWh, is less than
the off-grid generation cost of the country which is estimated between 0.3$/ 𝑘𝑊ℎ and
0.4$/ 𝑘𝑊ℎ [9]. The authors concluded that since the research was feasible and cost-effective
for small-scale hydropower projects, this should motivate the government and nongovernmental organizations to undertake such a project in the selected region of Ethiopia.
The literature [23] and [24] discuss the process of identifying hydropower resources in
remote areas using Geographic Information System (GIS) technology, and the application
of Multi-Criteria Decision Making (MCDM) methods [24] in the analysis of processed
geospatial data to find the optimal site location for hydropower development. The relevance
of these researches is that they provide helpful information to policymakers and concerned
agencies in hydropower resource management, planning, and development. Moreover, it
presents a reliable assessment for possible investors and brings benefits to the community
involved [23]. The design process of a hydropower plant passes through the modelling of its
components for the analysis of the dynamic operation through simulation. This has been as
well the interest of scholars. We can illustrate the papers [25] and [26] which discuss the use
of Simulink software of Matlab, in the dynamic modelling of the hydropower plant
components. The authors described the way the main components of hydropower plants
19
such as the synchronous machine, the hydro turbine, the penstock, and the excitation system,
can be modelled using Matlab to facilitate the dynamic study of the hydropower system.
This gives a better way to model and analyse any hydropower plant before its physical
implementation. The literature [26] suggested that modern control systems such as fuzzy
logic and PID control logic should be incorporated into a hydraulic turbine model to maintain
the stability of the output voltage.
2.2.2. Literature review on interconnected systems
In recent years, rising interest in interconnected systems has emerged due to the high
growth of distributed generations based on renewable energies. The advantage of these
renewable energies is that they are technically economic, the environmental impacts are
reduced, and they have more social benefits unlike non-renewable energies [17]. However,
they are mostly found in remote areas, where long transmission and distribution lines would
be required to supply the scattered loads from a single grid network. This fact causes a
significant voltage drop at the end of the transmission lines. This voltage drop in
transmission lines can be reduced by interconnecting the distributed energy resources, such
as hydropower, solar, etc. Many studies have been undertaken in this area, but, most of them,
were interested in the hybrid interconnection of pumped storage-battery or small-scale
hydropower combined with other resources such as solar or wind [27], [28], [29]. Among
the few that have talked about a general assessment of large and small hydropower plants
and their interconnection to the local grid network, some recent ones are revised here. The
literature [30] presents a design procedure to integrate pico-hydro generators into the grid
using conventional and widespread photovoltaic inverters. The authors found that since the
flow of a river may vary depending on the season, this may impact the efficiency of the grid
system when operating at different speeds of the hydro turbine. Therefore, to solve this issue
the authors suggested the use of photovoltaic inverters to interconnect hydropower units to
the grid. The MPPT integrated into the photovoltaic inverters will have to make sure that the
system is operating at maximum power even though the hydropower turbine operates at
different speeds. The paper [17] presents the major requirements for interconnecting Micro
Hydropower Plants. The authors tried to identify the main issues that may be encountered
when these MHPPs operate in Grid interconnected system. Moreover, some possible
solutions have been proposed in the same paper. The major requirements found are the
following: the respect to the conditions for synchronization of generators, the voltage of the
generator should be compatible with the voltage at the point of interconnection (whether it
is AC or DC), the safety for the whole system, and the consumers, the System monitoring
20
and control. Moreover, the grid interconnection issues and challenges presented were
gathered into technical and non-technical issues. The technical issues found in grid
interconnection are those related to power quality; to the operation and the control of the
system; and the loss of synchronization between generators. Non-technical issues that may
be encountered during the interconnection of Micro-hydropower schemes are those related
to the financing and the management of the whole project. Among the solutions proposed
we can mention: The use of new technics based on power electronic technologies for
automatic synchronization and control of the operation of the interconnected system. This
may maintain the reliability and the quality of the electricity supply [17]. Another study of
small hydropower plants (SHPs) connected to the grid through a tie line is presented in [31].
The authors analysed the case where small hydropower plants operate in island mode after
being disconnected from the main Grid due to the tripping of the tie line. This may happen
when a sudden fault appears in the Network. This causes a sudden unwanted load shedding
until the SHPs will be restarted. Unfortunately, the fact of restarting the SHP to reconnect
it to the distribution network leads to the low utilization of hydropower and long-time loss
of local load [32]. Thus, the reliability of the system is disturbed. To overcome this issue,
the paper proposes the use of a fast busbar automatic transfer switch (BATS). This bus can
connect quickly to the SHP which was disconnected from the Grid after meeting all
requirements of the grid-connected system [31]. The literature [33] presents Research on the
Reverse Power Mechanism of Grid-connected
Hydropower Units in asynchronous
networks. When a single unit is connected to the grid, the difference between the unit
frequency and the grid frequency is linear with the first fluctuation of the active power to the
system [33]. The more several units are connected to the grid, the more frequency
fluctuations are generated. To overcome this issue, they suggested that the grid connection
meet the following conditions: The active power transmitter used in the governor of the
hydropower plant has to play the role of measuring the reverse power; the design logic of
the power sampling device should be optimized. Moreover, the capacity of the generator unit
and the structure of the grid should be considered at the same time in the process of
connecting to the grid [33]. For our case, this study intends to assess all hydropower
resources of the North-Kivu province, and propose a model where the generating units will
be connected to the local grid network (SNEL). This will contribute to increase the electricity
access of the whole region by maintaining the reliability of the electricity supply.
21
3.
Chapter 3. DATA COLLECTION AND ANALYSIS
3.1 Collection of existing hydro data of rivers in North-Kivu province
The North-Kivu province is located in the East part of the DRC. It is bordered by
ITURI province in the North, the province of TSHOPO in the West, the SOUTH KIVU
province in the South, the Republic of Rwanda, and Uganda in the East. The province covers
an area of 59,486.52 𝐾𝑚2 , with 8,985,711 inhabitants according to the last statistics in
2018. The province is endowed with rich water resources and has promising hydropower
potential. However, since these hydropower resources are located in remote areas where
there have been several civil wars, they remain unexploited. Therefore, the majority of its
territories still have no access to electricity, which is a major hindrance to its economic
development. This province is composed of six territories which are: BENI (7484 𝐾𝑚2 ),
LUBERO (18,096 𝐾𝑚2 ) ,
MASISI (4734 𝐾𝑚2 ), NYIRAGONGO ( 333𝐾𝑚2 ),
RUTSHURU ( 5 289 𝐾𝑚2 ), WALIKALE (23,475 𝐾𝑚2 ) , plus the capital city GOMA
(75.52 𝐾𝑚2 ). The North-Kivu province was part of a national study done on renewable
energy assessment in the DRC, carried out in 2014 by the UNDP. This study, which is
commonly referred to as the Atlas of renewable energies in DRC, identified the hydropower
potential of each territory. However, the report does not provide detailed information on the
geological, geographical, and metrological conditions of the sites. It provides different maps
where all hydropower potential of rivers in each territory are identified by their respective
technical capacities. These technical power capacities will be evaluated and compared to the
local electricity demand. In general, the maximum load at a point in time is called an electric
demand (measured in 𝑘𝑊). The demand in a given region depends on how loads are being
connected to the network from time to time. To predict the load, the demand factor (𝐷𝐹) and
the diversity factor (𝐷𝑖𝑣𝐹) are often used. Each type of load possesses its 𝐷𝐹 and 𝐷𝑖𝑣𝐹,
depending on its magnitude. The maximum demand for a given consumer can be obtained
by multiplying his total connected loads and their respective 𝐷𝐹 . In the case of the
transformer, the maximum demand can be found by the summation of all maximum demands
of consumers divided by the 𝐷𝑖𝑣𝐹𝑠 between them. In this study, the maximum demand of a
group of loads will be determined by the following equation:
𝑃 = ( ∑4𝑖=1 𝐾𝑖 × 𝐶𝑖 ) × 1.2
(3.1)
Where the subscript i represents the group of loads ( 𝑖 = 1 corresponds to domestic loads;
𝑖 = 2 corresponds to commercial loads; 𝑖 = 3: Industrial loads; 𝑖 = 4: Municipal loads and
22
the value 1.2 is the extension factor. The constants 𝐾𝑖 and 𝐶𝑖 , are given by the equations
below:
K i = Number of units × Installed power per unit
Ci =
(3.2)
Demand factor (DF)
Diversity Factor(DivF)
(3.3)
The factors for the groups of loads as recommended by the International Electric
Commission (IEC) are given in Table 3-1.
Table 3-1: Different factors for a group of loads [34], [35]
i
Group of loads
1
2
3
4
Domestic loads
Commercial loads
Industrial loads
Municipal loads
Demand
factor (DF)
0.4
0.7
0.95
0,55
Diversity
factor (DivF)
2
1.46
1.4
1.45
Ci
0.20
0.48
0.68
0.34
The electricity demand for a given region requires as much granularity as possible,
with a preliminary geographical scanning of the population and on-the-ground surveys,
based on statistically significant sample sizes of the different demand segments [36].
Regarding the actual situation of the province with multiple repetitive civil wars, it is not
easy to undertake such a task. Therefore, some estimations will be carried out based on
standard loads.
3.1.1 Hydropower potential assessment in BENI territory
BENI territory covers an area of 7,484 𝑘𝑚2 , with a population of about 1,399,915
inhabitants in 2019. Statistics conducted in [37] revealed that 73% of the population in this
territory is still living in poor conditions, and their main activity is farming. The remaining
27% mostly undertake commercial activities. Four categories of households have been
identified in this territory: Very low-income household category (37%) with 5 persons per
household, low-income category (36%) with 8 persons per household, medium-income
category (23%) with 11 persons per household, and high-income category (4%) with 12
persons per household [37]. Comes up from this study that the higher the number of families,
the higher the income of the family. BENI possesses an actual coverage of electrification of
18.6% for 1,399,915 inhabitants, with a growth rate of 3.24% yearly. By taking the
average household size of 9 persons, the total number of households in the territory will be
155,546. This means around 126,614 households have no access to electricity. Studies
23
conducted in [1] reveal 31 sites with hydro potential for the possible future development of
hydropower plants, regionally distributed in the whole territory as identified in Fig.3-1. It
can be seen that the territory is endowed with a huge hydropower potential where only a few
are exploited.
Fig. 3-1: Hydrological map of BENI territory [1]
Apart from the unidentified sites because of the insecurity in the region, the available sites
where hydropower development is possible are summarized in Table 3-2, with their
respective classifications depending on their size. The huge hydropower potential in BENI
territory is ranged in Micro hydropower plants ( 10 𝑆𝑖𝑡𝑒𝑠 ), Mini hydropower plants
(7 𝑠𝑖𝑡𝑒𝑠), small hydropower plants (11 𝑆𝑖𝑡𝑒𝑠), and Medium hydropower plants (3 𝑆𝑖𝑡𝑒𝑠).
This leads to the total exploitable hydropower of 229,320 kW (229.32MW). This territory
is located in the North-East region of the North Kivu province, where it is observed abundant
rainfalls throughout the year. Therefore, the flow of rivers may remain constant throughout
the year. This constitutes an advantage for electricity generation without any seasonal
disturbances.
24
Table 3-2: Identified hydropower sites in BENI Territory
#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Site
Mabalako
Butuhe1
Isale Graben
Ngazi
Bulongo
Beni Peltac
Beni kin Soir
Beni Regideso
Mwenda2
Eringetti
Byatu
Oicha
Mutsora
Lume
Mabuku 1
Chochota
Lwavulanzira
Mabuku
Malese
Luhulu
Mutwaba 3
Mutwanga 3
Ruwenzori
Mutwanga1
Mutwaba 2
kisalala
Mutwanga2
Ibanda
Semiliki 1
Mahuma
Semiliki 2
Total power
Potential (kW)
13
37
41
41
48
51
51
68
75
88
100
246
250
300
411
500
700
2000
3000
3000
3500
3500
6000
6000
7500
7500
7500
7800
72000
2500
72000
229.32
Classification
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Medium hydropower plant
Small hydropower plant
Medium hydropower plant
3.1.1.1 Estimation of the local electricity demand
i. Estimation of the actual domestic demand
The assumption here takes into account a standard household with commonly used
appliances as shown in Table 3-3. It is found that the average power per household is around
3387.6 𝑊. Taking the total households without access to electricity of 126,614, the total
electricity demand (𝑃1 ) for households in the whole territory can be estimated using the
following equation:
P1 =K1 x C1
(3.4)
25
Where 𝐾1 represents the total households multiplied by the individual average load and
𝐶1 = 0.20 for domestic loads.
Thus: 𝐾1 = 3387.6 𝑊 𝑥 126 614 = 428.92 𝑀𝑤.
Therefore: 𝑃1 = 428.92 𝑥 0.2 ≈ 𝟖𝟓. 𝟕𝟖𝟒 𝑴𝒘
Table 3-3: Residential loads for standard households
Appliances
Units
Lighting
Socket-Outlet
Refrigerator
Kettle
Electric stove
Electric Iron
Electric fan
12
6
1
1
1
1
1
Unit Power
(W)
18
73,3
200
1000
1800
1000
300
Total Connected
(W)
216
440
200
1000
1800
1000
300
DF
0.6
0.2
0.7
0.5
0.7
1
0.9
Demand
(W)
129.6
88
140
500
1260
1000
270
3387.6
ii. Estimation of electricity demand for commercial loads
Commercial loads include banks, stores, shops, office buildings, telephone and
battery charging shops, etc. This territory counts 1203 business operators and 23 nongovernment organizations [38]. The total units of commercial loads will be 1226. Table 34 gives the average power consumption per unit. Therefore, the total electricity demand (P 2)
for commercial loads can be calculated by the formula below:
P2 = K 2 x C2
Where
the
constants
(3.5)
𝐾2 = 2826.7 𝑊 𝑥 1226 = 3.5 𝑀𝑊
,
and
𝐶2 = 0,48
Therefore, the total power demand for commercial loads will be:
𝑃2 = 4.15 𝑥 0.48 ≈ 𝟏. 𝟕 𝑴𝑾
Table 3-4: Estimated power consumption for commercial loads
Appliances
Units
Lighting
Socket-Outlet
Printer and scanner
Refrigerator
Kettle
Air conditioner
18
10
2
1
1
1
Power per
unit (W)
36
63,5
700
200
1000
500
26
Total connected
load (W)
648
635
1400
200
1000
500
DF
0.9
0.1
0.4
0,6
1
1
Demand
(W)
583.2
63.5
560
120
1000
500
2826.7
iii. Estimation of industrial loads
Table 3-5: Industrial loads in BENI territory
Appliances
Units
Power per
unit (kW)
14
43.3
18.6
18
20
6.5
22.5
45
3000
50
50
16.7
5
5
100
Total connected
loads (kW)
70
259.8
372
180
700
260
450
900
3000
500
1250
1035.4
25
100
1000
DF
Demand
(kW)
Slaughterhouse
5
0.75
52.5
Cold room
6
0.6
155.9
Rice and peanut sheller
20
0.7
260.4
Carpentry
10
0.75
135
Mill
35
0.8
560
Small craft
40
0.5
130
Sawmill
20
0.6
270
Coffee Industry
20
0.75
675
Brewery
1
1
3000
Oil mill
10
0.7
350
Soap factory
25
0.5
625
Telecommunication sites
62
0.75 776.6
Ice Candy Units
5
0.5
12.5
Repair Workshops
20
0.4
40
Others
10
0.75
750
7792.8
There are many types of industries which are different in their size. Thus the
electricity demand in this sector will be defined by the type of industry. In BENI territory, it
is found that the majority of small-scale industries require around 25 𝑘𝑊 , and some
medium-scale industries require a power between 25𝑘𝑊 and 100 𝑘𝑊. In the range of largescale industries that require above 500 𝑘𝑊, there is one brewery whose demand is 3 𝑀𝑊.
Table 3-5 gives the estimated industrial loads in the territory. The total demand for industrial
loads will be:
P3 =K3 x C3
(3.6)
Therefore: 𝑃3 = 7792,8 𝑥 0.68 ≈ 𝟓. 𝟑𝑴𝑾
iv. Estimation of electricity demand for municipal loads
Table 3-6 gives the estimated power needed by these loads. Here, we assume that the
street lighting will cover a length of 107𝑘𝑚. The number 𝑵 of lighting units to be installed
can be calculated by the formula below:
N=
Length of the way to be lighted
+ 1
Distance between two structures
(3.7)
Therefore, taking the distance between two structures of 40 𝑚, the total number of structures
will be:
27
𝑁=
107000
40
+ 1 = 2676 𝑠𝑡𝑟𝑢𝑐𝑡𝑟𝑒𝑠
Table 3-6: Estimated municipal loads in BENI territory
Appliances
Units Power per Total connected
unit (kW)
loads (kW)
Theatre halls
20
1
20
Radio stations
5
0.5
2.5
Street lighting
2676
0.1
267.6
Marriage places
25
5
125
Hotels and restaurants 50
25
1250
Churches
100
10
1000
Hospitals
140
100
14000
Public offices
20
3
60
Water pumping
22
100
2200
Schools
897
25
22425
DF
0.75
0.55
1
1
0.75
0.7
0.75
0.7
0.7
0.7
Demand
(kW)
15
1.375
267.6
125
937.5
700
10500
42
1540
15697.5
29826
The total demand for the municipal load will be:
𝑃4 = (29826 𝑥 0.34) = 𝟏𝟎. 𝟏𝟒 𝑴𝑾
3.1.1.2 Total electricity demand for BENI territory
Taking an extension factor of 1.2, the total electricity demand in the territory will be
𝑃 = (85.784 + 1.7 + 5.3 + 10.14) 𝑥1.2 = 𝟏𝟐𝟑. 𝟓 𝑴𝑾
The difference between the total hydropower potential in BENI territory and its actual
electricity demand gives 𝟏𝟎𝟓. 𝟖𝟐 𝑴𝑾 of excess that can be shared with the other territories,
assuming the hydropower potential is being exploited.
3.1.2 Hydropower potential assessment in LUBERO territory
The two territories BENI and LUBERO are located in the North-East part of the
province. They have a common frontier with Uganda in the East, in the North with
ORIENTALE province, in the south with RUTSHURU territory and West with WALIKALE
territory. Since LUBERO territory is crossed by the equator, it possesses regular rainfall
throughout the year. The assessed hydropower potential in the region as presented in Fig. 32 shows an abundant hydro resource that can contribute to the electricity supply in the region.
The total exploitable hydropower capacity in the whole territory is summarized in Table 37. This hydro potential includes micro hydropower plants (11 𝑆𝑖𝑡𝑒𝑠), mini-hydro power
plants (13 𝑠𝑖𝑡𝑒𝑠), small hydropower plants (15 𝑠𝑖𝑡𝑒𝑠), and one medium hydropower plant.
This leads to a total hydropower potential of about 83.64𝑀𝑊.
28
Fig. 3-2: Hydropower potential in LUBERO territory [1]
This territory has a very low rate of electrification of about 1%. Its population is
estimated to be 1,558,918 currently. By taking a household size of 9 persons, the actual
population represents about 173,213 households, from which 171,481 households do not
have access to electricity.
29
Table 3-7: Identified hydropower sites in LUBERO Territory
#
Site
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Lubango
Kasegbe
Muhangi
Butembo Kyambogho
Kipese
Bingi
Musienene
Mutiri
Butembo mundi
Masereka
Luvira
Butembo Ngengere
Mususa
Mighowe
Butembo Loulo
Butembo
Mangweredjipa
Mangweredjipa1
Bukano
Kayna
Luvughi
Kilombindo
Kanyabatonga
Butembo 1
Ivugha 1
Kasalala
Bukano
Lubero
Kavatengeza
Talihya
Lwavulanzira
Lowa(Niangu)
Bukano
Kirumba
Ivugha
Luonzo
Luango Lac
Talya Sud
Kisalala
Kanova
Potential
(kW)
14
20
20
25
27
30
50
50
61
72
100
102
102
109
150
180
200
400
400
411
500
700
700
915
1000
1000
1700
1700
2000
2000
2500
3900
4000
4000
5000
5000
5000
7000
7500
25000
83638
30
Classification
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Micro Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Medium hydropower plant
3.1.2.1 Estimation of LUBERO’s electricity demand
i. Estimation of the domestic load in LUBERO territory
The power of 3387.6 𝑊 as calculated previously is taken as the average electricity
demand for a standard household in all territories. Therefore, the total household power
demanded will be:
𝑃1 = 3387.6 𝑥171,481 𝑥 0.2 = 𝟏𝟏𝟔. 𝟏𝟖𝑴𝑾
ii. Estimation of the commercial load
In the LUBERO territory, 6.4% of the households undertake small businesses, and
6.4% are wage-earning [39]. The previously estimated electricity demand per unit for
commercial loads in BENI territory is assumed to be the same in all territories. By assuming
that 12.8% of the total households with no access to electricity constitute this sector, the
total commercial load can be calculated as follow:
K 2 = 2826.7W x times the number of commercial units
(3.8)
The number of commercial units = 171,481 × 0.128 = 21950 𝑢𝑛𝑖𝑡𝑠
Therefore: 𝑃2 = 21950 × 2826.7 × 0.48 ≈ 𝟐𝟗. 𝟖 𝑴𝑾 .
iii. Estimation of the industrial electricity demand in LUBERO Territory
Table 3-8: Estimation of industrial loads in LUBERO territory
Loads
Units
Coffee Industry
Cold room
Joinery
Mill
Oil mill
Rice and peanut husker
Sawmill
Slaughterhouse
Small craft
Soap factory
Telecommunication sites
Others
6
11
4
10
12
14
4
9
42
20
62
30
Unit Power
(kW)
36.8
60.8
71.3
24
21
31.4
146.8
14.7
6.8
50
16.7
50
Total connected
load (kW)
220.8
668.8
285.2
240
252
439.6
587.2
132.3
285.6
1000
1035.4
1500
DF
0.75
0.6
1
0.8
0.7
0.7
0.6
0.75
0.5
0.5
0.75
0.7
The total demand for industrial loads will be: 𝑃3 = 4449.1𝑥0.68 ≈ 𝟑 𝑴𝑾
31
Demand
(kW)
165.6
401.28
285.2
192
176.4
307.72
352.32
99.225
142.8
500
776.55
1050
4449.1
iv. Estimation of municipal loads in LUBERO territory
Table 3-9: Estimated municipal loads in LUBERO territory
Appliances
Units
Theatre halls
Radio stations
Street lighting
Marriage places
Hotels and restaurants
Churches
Hospitals
Public offices
Water pumping
Schools
15
4
2451
30
70
70
131
20
24
994
Power
per unit
(kW)
2
0.5
0.1
5
25
10
100
3
100
25
Total
connected loads
(kW)
DF
Demand
(kW)
30
2
245.1
150
1750
700
13100
60
2400
24850
0.75
0.55
1
1
0.75
0.7
0.75
0.7
0.7
0.7
22.5
1.1
245.1
150
1312.5
490
9825
42
1680
17395
31163.2
The total demand for municipal loads will be:
𝑃4 = 31163.2 𝑘𝑊𝑥0.34 ≈ 𝟏𝟎. 𝟔 𝑴𝑾
3.1.2.2 Ca1culation of the total electricity demand in LUBERO territory
The total electricity demand in LUBERO territory will be:
𝑃 = (116.18 + 29.8 + 3 + 10.6)𝑥1.2 = 𝟏𝟗𝟏. 𝟓 𝑴𝒘
It can be seen that the hydropower potential assessed cannot cover the total electricity
demand in this territory. Since this territory is closer to BENI territory, the local electricity
demand can be met by load sharing between these territories via an interconnected network
and by taking into consideration other available energy resources.
3.1.3 Hydropower potential assessment in MASISI territory
The hydropower potential in MASISI territory is presented in Fig. 3-3. The available
hydropower potential sites as presented in Table 3-10, are composed of One Micro
hydropower site, Three Mini hydropower sites, and Six Small hydropower plants. This leads
to a total of around 𝟏𝟕 𝑴𝑾 that can be harvested from the identified rivers. The actual
population is estimated at around 817,947 inhabitants. With an average size of 9 persons
per household, the actual population leads to a total of 90,883 households in the territory,
where, only 816 households have access to electricity.
32
Fig. 3-3: Hydropower potential assessed in MASISI territory [1]
Table 3-10. Identified hydropower sites in the MASISI territory
#
1
2
3
4
5
6
7
8
9
10
Site
Wau
Nyabiondo
Sake
Shosha
Masisi
Loashi
Nyakisuma
Mweso
Ngingwe
Oso
Potential (kW)
50
135
200
400
1300
2800
3000
3000
3000
3090
16975
Classification
Micro Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
Small hydropower plant
3.1.3.1 Estimation of MASISI’s electricity demand
i. Estimation of the domestic loads
By taking the average power per household of 3387.6 𝑊 , the actual domestic
demand will be calculated as follow:
𝐾1 = 3387.6 𝑊𝑥 90067 = 305.11 𝑀𝑊.
Therefore, the electricity demand for households will be:
𝑃1 = 305.11𝑥 0.2 ≈ 𝟔𝟏 𝑴𝒘.
33
ii. Estimation of the commercial loads
This sector is composed of 524 business operators and 19 non-government
organizations [40]. Therefore, the electric power needed will be:
𝑃2 = 2826.7𝑊 𝑥 543 𝑥 0.48 ≈ 𝟎. 𝟕𝟒 𝐌𝐰 ,
Where 2826.7 𝑊 is the average connected load for a single unit, and 𝐶2 = 0.48.
iii. Estimation of the electricity demand for industrial loads
The industrial loads are dominated by small industries as can be seen in Table 3-11.
Mining constitutes the most electricity consumer in this territory. The industrial loads can
be derived as follow:
𝑃3 = 21909.2𝑊𝑥 0.68 ≈ 𝟏𝟒. 𝟗 𝑴𝒘
Table 3-11: Estimated industrial loads in MASISI territory
Loads
Slaughterhouse
Cold room
Rice and peanut husker
Carpentry
Mill
Small craft
Sawmill
Coffee Industry
Telecommunication Sites
Mining
Others
Units Unit Power Total connected
(kW)
loads (kW)
DF
1
4
9
5
5
22
5
2
16
10
30
0.75
0.6
0.7
0.75
0.8
0.5
0.6
0.75
0.75
1
0.7
10
60
20
18
20
6.8
38
30
16.7
2000
50
10
240
180
90
100
149.6
190
60
267.2
20,000
1500
Demand
(kW)
7.5
144
126
67.5
80
74.8
114
45
200.4
20,000
1050
21,909.2
iv. Estimation of the electricity demand for municipal loads
Table 3-12 presents the estimated municipal loads in this territory. The total
electricity demand for municipal loads in this territory can be derived as follow:
𝑃4 = 26939.2 𝑥0.34 ≈ 𝟗. 𝟏𝟔 𝑴𝑾
34
Table 3-12: Estimated municipal loads in MASISI territory
Loads
Units
Theatre halls
Radio stations
Street lighting
Marriage places
Hotels and restaurants
Churches
Hospitals
Public offices
Water pumping
Schools
5
4
5001
10
20
30
82
30
10
1103
Power
per unit
(kW)
2
0.5
0.1
5
25
10
100
3
40
25
Total
connected
loads (kW)
DF
Demand
(kW)
10
2
500.1
50
500
300
8200
90
400
27575
0.75
0.55
1
1
0.75
0.7
0.75
0.7
0.7
0.7
7.5
1.1
500.1
50
375
210
6150
63
280
19,302.5
26,939.2
3.1.3.2 Calculation of the total electricity demand in the MASISI territory
The total electricity demand in this region will be:
𝑃 = (𝑃1 + 𝑃2 + 𝑃3 + 𝑃4 )𝑥1.2 = (61 + 0.74 + 14.9 + 9.16)𝑥1.2 = 𝟏𝟎𝟑 𝑴𝑾.
It is found that the local hydropower potential of 17 𝑀𝑊, is not sufficient to cover the total
electricity demand in MASISI territory. Therefore, to cover this gap, other sources need to
be taken into account.
3.1.4 Hydropower potential assessment in RUTSHURU territory
The territory possesses a huge hydropower potential, unfortunately, it remains
unassessed because of the insecurity in the region. The only assessed sites are presented in
Table 3-13, ranging in Micro hydropower units (2 𝑆𝑖𝑡𝑒𝑠), Mini hydropower units (5 𝑆𝑖𝑡𝑒𝑠),
and Small hydropower units (2 𝑠𝑖𝑡𝑒𝑠).
Table 3-13: Hydro potential sites in RUTSHURU territory
#
1
2
3
4
5
6
7
8
9
Site
Kikuku1
Kibungu
Bambu
Rwanguba
Katale
Katale1
Kikuku
Kivale
Rutshuru
Potential (kW)
20
28
200
300
300
300
820
1200
4000
7168
35
Classification
Micro Hydropower plant
Micro Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Small hydropower plant
Small hydropower plant
A total of about 7.2 𝑀𝑊 has been identified on different rivers as presented in Fig. 3-4. The
actual population is estimated at 1,843,408 inhabitants. With a household size of 9 persons,
the actual population gives 204,823 households. The actual rate of access to electricity in
this territory is around 5%. Therefore, 194,582 households are still living without access to
electricity in this territory.
Fig. 3-4: Identified rivers in RUTSHURU territory
3.1.4.1 Estimation of RUTHURU’s electricity demand
i. Estimation of the domestic loads
The total domestic demand can be calculated as for previous cases, by taking the
average per household of 3387.6 𝑊. Therefore, the total domestic loads can be calculated
as follow:
𝑃1 = 3387.6 𝑊𝑥194,582𝑥0.2 = 𝟏𝟑𝟏. 𝟖𝟑 𝑴𝒘
ii. Estimation of the commercial loads.
As reported in [39], agriculture constitutes the principal activity in this territory. It
represents around 88.7% of households, whereas 11.3% of the households undertake
commercial activities. This leads to 21,988 households that constitute this sector plus 64
non-government international and local organizations. For an average power of 2826.7 𝑊
per unit, the total power needed for this sector will be:
𝑃2 = 2826.7 𝑊 𝑥 22052𝑥 0.48 ≈ 𝟐𝟗. 𝟗𝟐 𝐌𝐰
36
iii. Estimation of the industrial loads.
The estimated industrial loads are presented in Table 3-14. It can be seen that only
small industries are found in this territory. This is justified by the fact that; this sector
intervenes mainly in the processing of agricultural products. The estimated connected
industrial loads are around 4259.7 𝑘𝑊. By applying the demand factor and the diversity
factor represented by the constant 𝐶3 = 0.68, the total electricity demand can be derived as
follows:
𝑃3 = 4 259,73𝑥0.68 ≈ 𝟐. 𝟗 𝑴𝑾
Table 3-14: Estimated industrial loads in RUTSHURU territory
Appliances
Units Unit Power
(kW)
Mill
Rice and peanut husker
Slaughterhouse
Cold room
Sawmill
Small craft
Carpentry
Telecommunication Sites
Coffee Industry
Others
60
20
4
2
20
50
20
9
2
30
20
20
10
60
30
3
15
16.7
30
100
Connected
loads (kW)
DF
1200
400
40
120
600
150
300
150.3
60
3000
0.8
0.7
0.75
0.6
0.6
0.5
0.75
0.75
0.75
0.7
Demand
(kW)
960
280
30
72
360
75
225
112.725
45
2100
4 259.73
iv. Estimation of municipal loads in RUTSHURU territory
Table 3-15: Estimated municipal load in RUTSHURU territory
Appliances
Units
Theatre halls
Radio stations
Street lighting
Marriage places
Hotels and restaurants
Churches
Hospitals
Public offices
Water pumping
Schools
20
8
3001
15
40
80
96
60
4
782
Power per
unit (kW)
2
0.5
0.1
5
25
10
100
3
50
25
Total connected
loads (kW)
DF
40
4
300.1
75
1000
800
9600
180
200
19550
0.75
0.55
1
1
0.75
0.7
0.75
0.7
0.7
0.7
Demand
(kW)
30
2.2
300.1
75
750
560
7200
126
140
13685
22868.3
Therefore, the total municipal load will be:
𝑃4 = 22868.3𝑥0.34 = 𝟕. 𝟖 𝑴𝑾
37
3.1.4.2 Calculation of the total electricity demand in the RUTSHURU territory
The total electricity demand in this territory will be:
𝑃 = (𝑃1 + 𝑃2 + 𝑃3 + 𝑃4 )𝑥1.2 = (131.83 + 29.92 + 2.9 + 7.8)𝑥1.2 ≈ 𝟐𝟎𝟔. 𝟗𝟒 𝑴𝑾.
It is found that the local demand is greater than the assessed hydropower potential in the
region. Therefore, an interconnection of this territory to other territories and the exploitation
of other alternatives for power generation would contribute to the supply of this total
demand.
3.1.5 Hydropower potential assessment in WALIKALE territory
WALIKALE is the largest territory in the province of North Kivu, with 39.46% of
the surface, and the only one with no electricity infrastructures [41].
Fig. 3-5: Hydropower potential of rivers in WALIKALE territory
The territory counts around 124,655 households without access to electricity. This affects
directly the economic development of the territory. 60 % of the households in this territory
undertake agriculture; whereas, 20 % are working in the mining sector, and only 10 %
undertake commercial activities. The remaining portion undertakes small craft activities.
Apart from the insecurity issue, road infrastructures in WALIKALE are disastrous and
38
worsen the isolation of some regions. Therefore, some hydropower potential of some rivers
remains unassessed. Identified rivers and their hydropower potential are presented in Table
3-16. Fig. 3-5 shows their locations on the WALIKALE’s map.
Table 3-16: Assessed hydropower potential sites in WALIKALE territory
#
2
3
7
5
6
8
Site
Walikale2
Walikale
Osso
Ulilu
Osokari
Kalundu(Lowa)
Potential (𝒌𝑾)
30
80
600
600
600
20000
21,910
Classification
Micro Hydropower plant
Micro Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Mini Hydropower plant
Medium hydropower plant
From Table 3-16, it can be seen that the territory possesses around 21.91𝑀𝑊 from assessed
rivers classified into 3 Micro hydropower plants, 3 Mini hydropower plants, and One
Medium hydropower plant.
3.1.5.1 Estimation of the electricity demand in WALIKALE territory
i. Estimation of the domestic electricity demand
By taking the average of 3,387.6 𝑊 per household, the total household demand will
be:
𝑃1 = 3,387.6 𝑊𝑥124,655𝑥0.2 = 𝟖𝟒. 𝟒𝟔 𝑴𝑾
ii. Estimation of the commercial loads
This sector is composed of 840 business operators and 72 non-government
organizations [42]. This leads to a total of 912 commercial units. Taking the average of
2826.7 𝑊 per unit, this leads to an electricity demand of:
𝑃2 = 2826.7 𝑊 𝑥 912𝑥 0.48 ≈ 𝟏. 𝟐𝟒 𝑴𝑾
iii. Estimation of the industrial electricity demand
The estimated industrial loads in this territory are presented in Table 3-17. The total
electricity demand for industrial loads will be: 𝑃3 = 21,680.45𝑥0.68 ≈ 𝟏𝟒. 𝟕𝟒𝑴𝑾
This industrial electricity demand is dominated by mining, since it constitutes the most
electricity consumer in this territory. The remaining is composed of small industries that
help to process agricultural products of the local population.
39
Table 3-17: Estimated industrial loads in WALIKALE territory
Loads
Units
Unit Power
(kW)
Total connected
loads (kW)
DF
Mill
Rice and peanut husker
Slaughterhouse
Cold room
Sawmill
Small craft
Carpentry
Coffee Industry
Mining
Telecommunication Sites
Others
4
8
2
4
4
2
4
4
10
3
30
20
20
10
60
30
30
15
30
2000
21
50
80
160
20
240
120
60
60
120
20000
63
1500
0.8
0.77
0.75
0.6
0.6
0.5
0.75
0.75
1
0.75
0.7
Demand
(kW)
64
123.2
15
144
72
30
45
90
20000
47.25
1050
21680.45
iv. Estimation of municipal loads
Table 3-18: Estimated municipal load in MASISI territory
Appliances
Units
Theatre halls
Radio stations
Street lighting
Marriage places
Hotels and restaurants
Churches
Hospitals
Public offices
Water pumping
Schools
10
8
2001
10
90
90
77
75
20
643
Power per
unit (kW)
2
0.5
0.1
5
25
10
100
3
10
25
Total connected
loads (kW)
DF
20
4
200.1
50
2250
900
7700
225
200
16075
0.75
0.55
1
1
0.75
0.7
0.75
0.7
0.7
0.7
Demand
(kW)
15
2.2
200.1
50
1687.5
630
5775
157.5
140
11252.5
19909.8
The total electricity demand for municipal loads will be:
𝑃4 = 19909.8 × 0.34 ≈ 𝟔. 𝟖 𝑴𝑾
3.1.5.2 Calculation of the total electricity in WALIKALE territory
The total electricity demand in the territory will be:
𝑃 = (84.46 + 1.24 + 14.74 + 6.8) × 1.2 = 𝟏𝟐𝟖. 𝟕 𝑴𝑾
The difference between the assessed hydropower potential and the actual electricity demand
for the region gives a huge gap, that can be covered by interconnection with other territories
or by other energy alternatives available in this territory.
40
3.1.6 Estimation of electricity demand in NYIRAGONGO territory
Nyiragongo territory shares the limits with RUTSHURU territory in the North, the
Republic of Rwanda in the East, Goma town in the South, and with MASISI territory in the
West. The territory does not have any hydropower sources. Its actual population is estimated
at 186,494 inhabitants and has an actual rate of electrification of 1.3 %. Agriculture which
is the main activity in this territory is composed of 70 % of the total population, whereas
commercial and livestock farming activities represent respectively 10 % and 20 % [43].
i. Estimation of the domestic electricity demand
This territory counts a total of 20,454 households without access to electricity. With
an average of 3387.6 𝑊 per household, the total household demand will be:
𝑃1 = 3387.6 𝑊𝑥20454𝑥0.2 = 𝟏𝟑. 𝟗 𝑴𝑾
ii. Estimation of the commercial loads
Taking 10 % of the households, there will be 2045 households undertaking
commercial activities. Thus, their electricity demand will:
𝑃2 = 2826.7 𝑊 𝑥 2045 𝑥 0.48 = 𝟏. 𝟒 𝑴𝑾
iii. Estimation of the industrial loads
Table 3-19: Estimated industrial loads in NYIRAGONGO territory
Loads
Units
Unit Power
(kW)
Total connected
loads (kW)
DF
Mill
Rice and peanut husker
Slaughterhouse
Cold room
Sawmill
Small craft
Carpentry
Coffee Industry
Soap factory
Repair Workshops
Telecommunication Sites
Others
20
8
3
2
15
30
10
2
10
20
6
30
20
20
10
60
30
3
15
30
50
5
19
100
400
160
30
120
450
90
150
60
500
100
114
3000
0.8
0.7
0.75
0.6
0.6
0.5
0.75
0.75
0.5
0.4
0.75
0.75
The total electricity demand for industrial loads will be:
𝑃3 = 3624.5𝑥0.68 ≈ 𝟐. 𝟒𝟔 𝑴𝑾
41
Demand
(kW)
320
112
22.5
72
270
45
112.5
45
250
40
85.5
2250
3624.5
v. Estimation of the municipal loads
Table 3-20:Estimated municipal loads in NYIRAGONGO territory
Appliances
Units
Power per
unit (kW)
Total
connected
loads (kW)
DF
Demand
(kW)
Theatre halls
Radio stations
Street lighting
Marriage places
Hotels and restaurants
Churches
Hospitals
Public offices
Water pumping
Schools
10
5
2726
10
35
40
12
30
2
234
2
0,5
0,1
5
25
10
100
3
50
25
20
2,5
272,6
50
875
400
1200
90
100
5850
0,75
0,55
1
1
0,75
0,7
0,75
0,7
0,7
0,7
15
1
273
50
656
280
900
63
70
4095
6403
The electricity demand will be:
𝑃4 = 6403𝑥0.34 = 𝟐. 𝟐 𝑴𝑾.
vi. Calculation of the total electricity demand in the NYIRAGONGO territory
The total electricity demand in this territory will be:
𝑃 = (13.9 + 1.4 + 2.46 + 2.2)𝑥1.2 ≈ 𝟐𝟒 𝑴𝑾
3.1.7 Estimation of the electricity demand in GOMA town
Goma town is the capital city of the North-Kivu province. It is located on the
Northern shore of Lake Kivu, next to the Republic of Rwanda. This town does not have any
rivers that can contribute to hydropower project development. Goma town is supplied by the
National Utility SNEL, through a line of around 5 𝑀𝑊 that comes from the Ruzizi1 power
plant in South Kivu province. Other private companies such as Virunga S.a.r.l, SOCODEE
and Nuru energy have been authorized to distribute energy in this town, and now they are
competing with the national utility SNEL. The company SOCODEE has financed a medium
voltage transmission line of 5 𝑀𝑊 from the Matebe hydropower plant, belonging to
Virunga S.a.r.l. This hydropower plant with a capacity of 13.1𝑀𝑊, located in Rutshuru
territory supplies actually a part of Goma town, Rutshuru, Nyiragongo, and Lubero
territories. On the other side, Nuru Energy has connected an off-grid solar power plant since
February 2020. This contributes to the supply of power to some quarters of Goma town, but
the electricity demand is still high in general. With the actual population estimated at around
42
2 million inhabitants, only 29.5% have access to electricity. Others are still using small
generators and solar systems to power their houses.
i. Estimation of domestic loads
The domestic loads are composed of 15666 households that do not have access to
electricity. Table 3-21 gives the estimated load in a single household in Goma town.
Table 3-21: Estimated household loads in Goma town
Appliances
Units
Lighting
Socket-Outlet
Refrigerator
Kettle
Electric stove
Electric Iron
Electric fan
Electric water heater
Home water pumping motor
12
6
1
1
1
1
1
1
1
Unit
Power
(W)
18
73.3
200
1000
1800
1000
300
2000
500
Total
Connected
(W)
216
440
200
1000
1800
1000
300
2000
500
DF
Demand
(W)
0,6
0,2
0,7
0,5
0,7
1
1
0,5
0,75
129,6
88
140
500
1260
1000
300
1000
375
4792,6
Taking the average of 4792.6 𝑊 per household, the total household demand can be
calculated as follow:
𝑃1 = 4792.6 𝑊𝑥15,666 𝑥0.2 ≈ 𝟏𝟓 𝑴𝑾
ii. Estimation of commercial loads
This sector constitutes the main activity in Goma town. Around 93.8% of
households undertake commercial activities. This leads to a total of 14,695 commercial
units.
Thus, the electricity demand by this sector will be:
𝑃2 = 2826.7 𝑊 𝑥 14,695𝑥 0.48 ≈ 𝟏𝟗. 𝟗𝟒 𝑴𝑾
43
iii. Estimation of industrial electricity demand
The estimation of these loads as presented in Table 3-22 takes into account the loads
that are not yet connected to the existing electricity utilities.
Table 3-22: Estimated industrial loads in Goma town
Loads
Units
Unit Power
(kW)
Total connected
loads (kW)
DF
Mill
Rice and peanut husker
Slaughterhouse
Cold room
Sawmill
Small craft
Carpentry
Juice industry
Telecommunication Sites
Soap industries
Other small industries
20
10
2
15
20
10
30
30
67
15
25
50
50
50
60
30
3
15
80
20
100
100
1000
500
100
900
600
30
450
2400
1340
1500
2500
0.8
0.7
0.75
0.6
0.6
0.5
0.75
0.75
0.75
0.75
0.75
Demand
(kW)
800
350
75
540
360
15
337.5
1800
1005
1125
1875
8282.5
Therefore, the total industrial load can be derived as follow:
𝑃3 = 8282.5𝑥0.68 ≈ 𝟓. 𝟔𝟑𝟐𝟏𝑴𝑾
iv. Estimation of municipal loads
Table 3-23: Estimated municipal loads in GOMA town
Appliances
Units
Power per
unit (kW)
Total
connected
loads (kW)
DF
Demand
(kW)
Theatre halls
Radio stations
Street lighting
Marriage places
Hotels and restaurants
Churches
Hospitals
Public offices
Water pumping
Schools
25
15
501
30
40
60
60
50
15
266
2
0,5
0,1
5
25
10
100
3
200
25
50
7,5
50,1
150
1000
600
6000
150
3000
6650
0,75
0,55
1
1
0,75
0,7
0,75
0,7
0,7
0,7
38
4
50
150
750
420
4500
105
2100
4655
12,772
The total municipal electricity demand will be:
𝑃4 = 12,772𝑥0.34 = 𝟒. 𝟑𝟒𝑴𝑾
44
v. Total electricity demand in Goma town.
Taking an extension factor of 1.2, the total electricity demand in Goma town will
be:
𝑃 = (15 + 19.94 + 5.6321 + 4.34)𝑥1.2 ≈ 𝟓𝟑. 𝟗 𝑴𝑾
3.2 Summary of the hydropower capacity and electricity demand in the province
The total hydropower capacity of rivers in North Kivu province as identified in
different territories is summarized in Table 3-24. The total electricity demand is ranged by
region, in terms of different groups of loads.
Table 3-24: Recapitulation of the total electricity demand in North-Kivu province
It can be seen from Table 3-24 that the total hydropower potential of the province is
estimated at 359.07 𝑀𝑊, of which Beni territory makes up 229.32 𝑀𝑊. It is followed by
Lubero territory with 83.64 𝑀𝑊 . Only two regions which are the Goma town and
Nyiragongo territory do not have any hydropower resources. The actual electricity demand
which has been evaluated at around 831.4 𝑀𝑊, can be covered at 43.2% by the hydropower
potential assessed in the whole province. Since some regions do not have enough
hydropower potential that can contribute to their electricity demand, there is a need for a
grid interconnected system to make the system more reliable, cost-effective and efficient.
To cover the total electricity demand at 100%, other energy resources available in the
province need to be taken into consideration. The other energy resources that are available
in the province are presented in the following section.
45
3.3 Other available energy resources in North Kivu province
The North-Kivu province possesses other energy resources that can contribute to its
electric power supply, unfortunately, they remain untapped. As summarized in Table 3-25,
apart from Biomass and Solar energy resources, the province possesses a tremendous
reserve of Geothermal energy due to its position in the Eastern African rift valley that is
composed of many volcanos. In addition to that, the Methane gas dissolved in lake Kivu
constitutes a significant energy potential that can contribute to supplying electricity and gas
for cooking to the local households. As mentioned in [44] and [45] the rate of increase of the
methane gaze in lake Kivu, is estimated at around 125 million of 𝑚3 per year due to the fact
that it is located near the volcano NYIRAGONGO. This constitutes a danger to the
surrounding population in case there is a volcano eruption into it. Since GOMA town is
located between Nyiragongo Volcano and Lake Kivu, it would be more affected in case of
such a disaster. Therefore, there is a need for such energy development in this province to
contribute to the local energy demand and the safety of the population.
Table 3-25: Other energy resources in North Kivu province [1]
Energy resources
Comments
Biomass potential
The annual energy that can be generated from this technology
is evaluated at around 76,583.74 𝑀𝑊ℎ . The biomass
resources can be found in all the territories of the North Kivu
province from agricultural scraps and its large forest reserves.
Solar potential
The average irradiance in the province varies from 4 to
5.5𝑘𝑊ℎ/𝑚2 /𝑑𝑎𝑦 . These values are favourable for solar
technology developments.
Geothermal
There is a huge geothermal potential that needs to be
potential
evaluated. Geothermal resources are found along the Eastern
Africa rift valley region that crosses BENI, LUBERO,
RUTSHURU, NYIRAGONGO territory and Goma town.
Natural Gaz
57 billions of 𝑚3 of methane gaze located in Kivu lake, which
borders the GOMA town and MASISI territory.
46
3.4 Forecast of the electric power demand in the province
Predictions of future events and conditions are called forecasts, and the act of making
such predictions is called forecasting [46]. Load forecasting can be divided into three
forecasting time horizons: short-term load forecasting which is usually from one hour to one
week; medium-term load forecasting which is usually from one week to one year; and longterm forecasting which is longer than one year [47]. Load forecasting can also be divided
into two categories based on the forecasting scope: regional load forecasting which provides
load forecasts for a large geographical area and busbar load forecasting which provides nodal
load information for network control functions [47]. This section will be based on long-term
regional load forecasting. Various approaches and models for the different types of
forecasting have been discussed in [48], [49], [50] and [51]. It has been shown that the
accuracy of these forecasting approaches depends on the availability of historical data and
requires more information about customers and their equipment. In addition to that, longterm forecasts incorporate economic and population dynamic forecasts, as well as industrial
construction and technological development as input parameters. Regarding the actual
pandemic situation, it is not easy to collect these required data, since it would require visiting
different government companies for data collection. As presented in [52], the electricity
demand in DRC is divided into two categories which are: the residential loads and the
industrial loads. These industrial loads include the commercial loads, municipal loads and
small, medium and large industries. Therefore, Eq. (3.10) will be used for load forecasting
by taking into consideration the fact that residential loads increase with an annual rate of
8.2% and 5.2% for industrial [52].
Pforecast=P*(1+r) n*LF
(3.9)
Where: 𝑛 is the number of years; 𝑟 represents the rate of power demand; 𝑃 is the actual
power demand; 𝐿𝐹 is the load factor.
The calculations will be conducted assuming that the load factor of residential,
commercial, industrial, and municipal loads is respectively 0.4, 0.45, 0.55, and 0.5 as
recommended by the IEC [34]. The gestation period for power plants, which are set up to
meet consumer demand, typically varies between 7 to 12 years in the case of thermal and
hydropower plants and 3 to 5 years for gas-based plants [49]. As a result, utilities must
forecast demand for the long run (10 𝑡𝑜 20 𝑦𝑒𝑎𝑟𝑠), make plans to construct facilities and
begin hydropower development before the indices of forecast growth reverse or slow down
[49]. For our case, the forecast will cover 10 years. Thus, using Eq. (3.10), the yearly
47
electricity demand for different categories of loads is presented in Table 3-26. It can be seen
that after one year, for example, the power demand for domestic, commercial, industrial and
municipal loads in the whole province will be increased respectively by 219.9 MW, 40.1
MW, 28,3 MW and 26.8 MW. The initial values taken for this forecast are the total actual
electricity demands that have been calculated previously and presented in Table 3-24. Table
3-26 shows that, after 10 years, the actual electricity demand of the North-Kivu province
that has been evaluated at 831.4 𝑀𝑊 would be increased by 716.9 𝑀𝑊. This would lead to
a total demand of 1548.3 𝑀𝑊. With such growth of electricity demand in this province,
there is a need to take into consideration other available energy resources as presented in
Table 3-25. For more reliability of the electric power supply in the whole region, a single
Grid interconnected network would be suitable.
Table 3-26: Load forecast in North Kivu province
Domestic Commercial Industrial Municipal Extension
Total
loads
loads (MW)
loads
loads
factor
demand
(MW)
(MW)
(MW)
(MW)
Year 1
219.9
40.1
28.3
26.8
1.2
378.2
Year 2
238,0
42.2
29.8
28.2
1.2
405.8
Year 3
257.5
44.4
31.3
29.7
1.2
435.5
Year 4
278.6
46.7
33,0
31.3
1.2
467.4
Year 5
301.4
49.1
34.7
32.9
1.2
501.8
Year 6
326.2
51.7
36.5
34.6
1.2
538.7
Year 7
352.9
54.4
38.4
36.4
1.2
578.4
Year 8
381.8
57.2
40.4
38.3
1.2
621.2
Year 9
413.1
60.2
42.5
40.3
1.2
667.3
Year 10
447,0
63.3
44.7
42.4
1.2
716.9
The design and simulation of this Grid interconnected system will be presented in
the following chapter.
48
4.
4. Chapter 4. DESIGN AND SIMULATION
In the previous chapter, the hydropower potential of rivers in North-Kivu province
has been presented. A total of 95 hydropower sites have been assessed ranging from Microhydropower to Medium hydropower units as summarized in Table 4-1.
Table 4-1: Total assessed hydropower sites in North Kivu province
Classification
Range
Micro-hydropower 13 to 88 kW
Mini-hydropower
Small hydropower
Medium
hydropower
100 to 915 kW
1 to 7.8 MW
20 to 72 MW
Application
Small remote communities,
isolated industries (Off-grid
systems)
Stand-alone or Mini-Grid
Mini-grid or grid-connected
Mini-grid or grid-connected
Total Sites
27
29
34
5
Total hydropower sites
95
The classification of these hydropower sites gives a wide range of possible
applications throughout the province. There is a possibility for Off-Grid, Mini-grid and Gridconnected system developments. Practically, the Micro and Mini-hydropower are installed
on small rivers with a small flow rate of water. The electric power generated from these
technologies fluctuates according to the season of the year. This makes these generations
unstable, requiring advanced control systems for a grid-connected network. Furthermore,
such stations generate a low power that needs to be consumed at the level where it is
generated without long transmission lines. At a long distance, the cost of transformers,
protection equipment and transmission lines may increase the capital cost for the generation
station. This may impact the cost of electricity for Micro-hydropower and Mini hydropower
stations which would not be affordable for consumers with low income. In case they are
connected to the main Grid, the cost of the Grid-connected system would be affected, as well
as the reliability of the whole system. Thus, advanced control systems need to be applied for
the better operation of such applications. Therefore, for more reliability and costeffectiveness, these technologies have to be connected to the Grid if they are located at near
distances from it. Otherwise, they have to be analysed as Off-Grid systems. This case will
not be part of this study. The Grid interconnected system that will be designed will take into
consideration the Small and Medium units. These units generally present negligible
fluctuation of their output power according to seasons of the year, for our case they are
located at near distances to one other (Which makes it easy to interconnect them to a common
local sub-station before reaching the Grid network). Also, their technical data ( Flow rate
and Head) are known as published in [1], which makes them easy to analyse. These
49
aforementioned facts justify their choice for the Grid-connected system that will be
proposed. The proposed system will constitute a foundation for the future integration of other
hydropower developments. The sites that will be considered for a Grid-Connected system
are presented in Table 4-2, with their respective technical power, flow rate, head and their
location in the province.
Table 4-2: Selected hydropower sites for Grid-Connected system
Site name
Loashi
Mweso
Lowa
Talya Sud
kisalala
Ibanda
Kalundu
Kanova
Mahuma
Semiliki 1
Semiliki 2
Capacity [Kw]
2800
3000
3900
7000
7500
7800
20000
25000
25000
72000
72000
Classification
SHPP
SHPP
SHPP
SHPP
SHPP
SHPP
Medium HPP
Medium HPP
Medium HPP
Medium HPP
Medium HPP
Q (m³/s)
13
10,2
8
3.57
15.28
15.9
117.7
25.48
63.71
120
120
H (m)
Territory
22
MASISI
30
MASISI
50
LUBERO
200 LUBERO
50
BENI
50
BENI
17
WALIKALE
100 LUBERO
40
BENI
61
BENI
61
BENI
4.1. Design of a Hydropower Grid-connected system
In this section, the discussion around the main components of a hydropower-Grid
connected system will be conducted based on known standards. The study concerns the civil
components, the Electromechanical components, and the Electrical design of a hydropower
plant. Furthermore, the interconnection requirements of a hydropower plant to the Grid will
be discussed. Since the topography, hydrology and geology characteristics vary according
to the natural conditions of a given region, the hydropower scheme layout development can
be different for selected sites [53]. The site-specific layout can contribute to optimizing the
use of required components and the exploitation of the available head and the water flow
[53]. In this work, a general study will be conducted, but for implementation, a specific study
is required as mentioned before.
4.1.1 Civil components
Civil components for a hydropower plant are all about the Headworks, the waterway,
the powerhouse, the tailrace and other structures that intervene in the protection of the
hydropower plant from environmental and working risks. The details about these
components are given in the following sections.
50
4.1.1.1 The headworks
The components that compose the headworks are the dam, the weir and the water
intake structure. The dam as well as the weir contribute to increasing the water level to the
desired elevation. They also protect the hydropower structure from flood effects whereas,
the role of the water intake structure is to safely change the direction of the water from the
river course to the waterway [53].
i. The Dam
As developed in [53], the classification of the dams depends on the function served,
Height, construction materials and sealing system. The criteria for the selection of the type
of dam during implementation are given in Table 4.3. It can be seen that the selection
depends strongly on the geological conditions of the hydro site.
Table 4-3: Selection of a type of dam [53]
ii. Weir
It is a structure, where the level of water is raised to the desired elevation in other to
aloud a big quantity of it to overflow. Thus, it helps to determine the flow rate of the river.
It differs from a dam by the fact that it diverts water at the intake, increases the water level
up to the desired head and diverts floodwaters safely. The ability of a given weir to regulate
the water level leads to different types of weirs. On one hand, weirs with movable elements
are used in case a constant water level is needed regardless of the discharge. On the other
hand, when Fixed overflow weirs are used, the upstream water level will change when the
51
streamflow changes. The weirs and dams must be well designed to be able to withstand all
possible mechanical and environmental loading conditions [53].
iii. Water intake structure
The water intake structure (water diversion structure) constitutes the highest point of
a hydro system, where a required amount of water is safely diverted from the main river into
the penstock that feeds the turbine. Different structures of water intake can be designed
depending on the geographical characteristics of the site. We can distinguish structures that
take water directly from the water flow and divert it to the penstock; Others divert the flow
through an auxiliary structure and some structures can be located in reservoirs. The process
of cleaning water before it reaches the pipeline is done through the following main
components of an intake:
• Screen (or settling basin): it contributes to removing floating scraps in water before
entering the penstock.
• The crane: it helps to remove solid particles brought by the flow of water in the
screen.
• Intake gate: It helps to stop the water flow during the time of penstock maintenance.
Depending on the site characteristics and the available type of turbine, the diversion
systems can be Opened or Closed. A closed diversion system is where water flows within
the pipe, without being affected by gravitational forces. Closed diversion systems work well
for developing high-pressure heads with relatively low water flow volumes, therefore, they
are suitable for impulse turbines [54]. Open diversion systems, convey water to the turbine
through an open canal. Thus, the water flow is directly exposed to gravity. Such systems are
suitable for supplying large volumes of water to the turbine with low friction losses.
Therefore, they can be applied to reaction turbines [54].
4.1.1.2 The waterway
It is composed of all components that direct water from the intake to the powerhouse,
such as the Sand trap, the headrace, the Forebay, the Surge tank (surge chamber) and the
Pressure pipe (penstock).
i. The sand trap (grit chamber)
During the operation of the HPP, suspended sediments in the water flow may wear
down the hydraulic steel structures and turbine if they are not removed before interring the
52
turbine. Therefore, the role of the sand trap is to ensure that all sediments are removed from
the water before it reaches the turbine. The presence of suspended sediments in water flow
has to be avoided in all types of hydropower developments since they can reduce their
efficiency as well as their lifespan. The acceptable size of the suspended sediments that can
remain in the water flow depends on the head of the hydropower site. In case the available
head is higher than 100𝑚, particles larger than 0.2 𝑚𝑚 have to be removed by the sand trap,
and for heads lower than 100m, particles larger than 0.3 𝑚𝑚 have to be stopped as well [53].
However, the sand trap can be omitted in large storage schemes with reservoirs because,
suspended sediments may have enough time to settle in the reservoirs, depending on the
stored volume of water.
ii. The headrace
The purpose of this structure is to convey the water safely towards the forebay or the
surge tank with minimum head losses, through one or a combination of the open channel
and the tunnels.
iii. Forebay
The forebay is a structure that brings to the HPP scheme the following features:
•
The penstock is connected to the headrace through the forebay;
•
During the start-up process, the forebay provides sufficient water volume to the turbine;
•
It prevents air from entering the penstock [53].
•
During the operation of a hydropower plant, the load rejection creates surge waves. Thus,
the role of the forebay will be to equalize these surge waves that would be dangerous to
the penstock.
iv. Surge tank (surge chamber)
The role of this structure is to control the variations of the water pressure in the
penstock and the headrace, to smooth the water hammer and also contribute to regulating
water flow to the turbine by providing the necessary retarding head.
v. Pipeline
The pipeline also called a waterway or penstock is a canal which conveys the diverted
water under pressure, from the forebay to the turbine. It is characterized by the materials
from which it is made, its diameter, the wall thickness and the type of its jointing system.
For optimal design of the penstock, the features below need to be taken into consideration:
53
•
The materials as presented in Table 2-1, are chosen according to their cost, the jointing
system, the weight, the accessibility and the geographical conditions of the hydropower
site. [55], [56].
•
Generally, a penstock with a large diameter is preferable because frictional losses would
be reduced, but its cost is high. Therefore, the designer has to balance between these two
facts, by making sure that the head loss does not exceed 4% as recommended by the
European small hydro association [55],[56].
•
The wall thickness is selected to accommodate the pressures encountered during plant
operation [55].
•
The penstock must be strong enough to withstand all sudden rises of the water pressure
due to the water hammer.
Depending on the size of the river, the designer can decide that each generating unit be
connected to its pipeline, or a single pipeline with several branches can distribute water to
different generating units. The optimum design of the penstock would help to reduce high
expenses in hydropower development [57], [55]. Some methods used to optimize this design
are discussed in [55], [58] and [59]. The diameter and the acceptable water velocity, are
designed within the feasible cost of the penstock, by taking into account head losses. These
losses depend on the type of material used, the length of the penstock and the thickness [53].
a. Determining the pipeline (penstock) diameter for selected hydropower sites
The diameter of the pipeline (penstock) can be calculated by the formula below as
developed in [55]:
4∗𝑄
𝐷 = √ 𝜋𝑉
(4.1)
Where D is the internal diameter of the penstock, 𝑄 is the water flow rate, and 𝑉 is the
velocity of the diverted water. If the velocity 𝑉 is unknown, it is required to assume a flow
velocity of 3 𝑚𝑒𝑡𝑒𝑟𝑠 per second which helps to find a rough diameter of the pipe. Based on
this rough value the optimum diameter of the penstock can be found [60]. In this way, by
using Eq. (4.4), the rough penstock diameter for selected sites will be respectively: 2.3m,
2.1m, 1.8m, 1.2m, 2.5m, 2.6m, 7.1m, 3.3m, 5.2m, 7.1m, and 7.1m. With detailed studies of
the hydro sites, and by using some appropriate software (RETScreen, Homer, etc.) the
optimum penstock diameter can be determined based on the rough diameter. In RETScreen
software, for example, the optimum diameter of the penstock can be determined in the Level
2 analysis, but it needs more data that describe correctly the site where the hydropower plant
54
will be built. This will not be part of this study since it would require more data that are not
accessible for the moment.
b. Determining the losses in the pipeline (penstock)
Practically, the total head that acts on the turbine is defined as the net head. It can be
expressed by the following equation:
𝐻𝑛 = 𝐻𝑔 − 𝐻𝑙𝑜𝑠𝑠
(4.2)
Where, 𝐻𝑛 is the net head (m), 𝐻𝑔 is the gross head (m) and 𝐻𝑙𝑜𝑠𝑠 is the total head loss in
the pipeline (m). The total head loss in the pipeline is composed of the longitudinal (𝐻𝑙𝑜𝑛𝑔 )
and the local losses (𝐻𝑙𝑜𝑐 ). It can be expressed by the following equation:
𝐻𝑙𝑜𝑠𝑠 = 𝐻𝑙𝑜𝑛𝑔 + 𝐻𝑙𝑜𝑐
(4.3)
The longitudinal losses are due to friction against the pipe wall, whereas, the local losses
(Minor losses) are caused by the turbulence. These two categories of losses can be calculated
respectively by the following equations:
𝐻𝑙𝑜𝑛𝑔 [𝑚] =
𝐻𝑙𝑜𝑐 [𝑚] =
𝜆 𝐿 𝑉2
(4.4)
2𝐷 𝑔
𝑘 𝑉2
2 𝑔
(4.5)
Where, 𝜆 is the friction coefficient of water in the penstock (Colebrook coefficient),
𝐿[𝑚] is the length of the penstock, and 𝑘 is the coefficient of local losses through bends
(𝐾𝑏 ), valves (𝐾𝑣 ), entrance (𝐾𝑒 ) and through a sudden contraction (Kc). By taking into
consideration the different values of 𝑘 , Eq. (4.8) can be written as follow:
𝐻𝑙𝑜𝑐 =
𝑉2
(𝐾𝑏 + 𝐾𝑣 + 𝐾𝑒 + 𝐾𝑐 )
2𝑔
(4.6)
The coefficient of friction (𝜆) depends on the value of the Reynolds Number (𝑅𝑒 ), and the
type of flow. It is determined by the expression shown in Table 4-4.
Table 4-4: Coefficient of friction depending on the Reynolds Number [58]
55
The Reynolds number is a dimensionless number used to categorize the fluids systems in
which the effect of viscosity is important in controlling the velocities or the flow pattern of
fluid [61]. Mathematically, it is expressed as the ratio of inertial forces to viscous forces.
𝑅𝑒 =
𝜌𝑉𝐷
𝜇
(4.7)
Where: ρ is the density of water (997𝑘𝑔𝑚 −3 ), V is the velocity of water, D is the penstock
diameter and μ is the viscosity of the fluid (8.9 × 10−4 Pa.s). The length of the penstock, the
velocity as well as the different losses are site-specific parameters. In this study the
estimation of the losses in the pipeline will be done by assuming that: The pipeline is made
of steel material, the velocity of the water through the pipeline 𝑉 = 3𝑚/𝑠, the length of the
pipeline 𝐿 = 300𝑚 and the plant is operating with a bi-plane valve (𝐾𝑣 = 0.3). The losses
will be split into entrance losses ( 𝑘𝑒 = 0.5), and others (losses due to bends, sudden
contraction, etc). These other losses can be evaluated by the following equation [60]:
𝑂𝑡ℎ𝑒𝑟 𝑙𝑜𝑠𝑠𝑒𝑠 = 5 𝑡𝑜 10% × (𝐻𝑙𝑜𝑛𝑔 + 𝐻𝑖𝑛𝑙𝑒𝑡 + 𝐻𝑣𝑎𝑙𝑣𝑒 )
(4.8)
Utilizing the above equations, the pipeline losses for the selected sites can be derived as
presented in Table 4-5.
Table 4-5: Calculated losses in the pipeline
Analysing the case of the LOASHI hydro site, for example, it can be proved that a large
diameter of the penstock leads to a reduction in head losses. This is shown in Fig. 4-1.
56
21,45
Net head
Energy loss
0,85
21,40
0,80
H (m)
0,75
21,30
0,70
21,25
Hloss (m)
21,35
0,65
21,20
0,60
21,15
0,55
2
3
4
5
6
7
8
D (m)
Fig 4-1: Net head and energy losses vs internal penstock diameter
c. Penstock Wall Thickness
Let's consider a penstock made of A-36 steel material. Thus, the minimum thickness
in 𝑚𝑚 of the wall can be calculated by the following equation:
𝑡 = [5.0764 × 10−5 ] × 𝐷 × 𝐻 × 1000
(4.9)
Therefore, for the selected sites, the minimum thickness of the pipeline will be respectively:
2.6𝑚𝑚 , 3.2𝑚 , 4.7𝑚𝑚 , 12.5𝑚𝑚 , 6.5𝑚𝑚 , 6.6𝑚𝑚 , 6.1𝑚𝑚 , 16.7𝑚𝑚 , 10.6𝑚𝑚 , 22.1𝑚𝑚 , and
22.1𝑚𝑚.
4.1.1.3 Powerhouse
All electrical and mechanical equipment that participate in the conversion of water
flow into electrical energy are stored in the powerhouse to be protected against extreme
weather conditions. Generally, the design of the powerhouse is done once the size and the
number of all electromechanical equipment are known. Other, key parameters that have to
be taken into account during the design of the powerhouse are as follows:
•
The geotechnical properties of the surrounding soils need to be studied;
•
The powerhouse should be built above any identified flood line of the river. This would
prevent ground sinking and the weakness of the foundation and civil structure;
•
It is required to identify the shallow water tables and the seasonally wet soils,
•
During the construction and operation stages, of the hydropower plant, the environmental
impacts should be kept to a minimum [57].
57
4.1.1.4 Tailrace
A tailrace is a structure that removes water from the powerhouse after passing
through the turbine. For better operation, it must be oriented downstream with a sufficient
slope in order to establish favourable flow conditions and prevents water from backing up
into the turbine.
4.1.2 Mechanical components
Mechanical components include the inlet valve, the turbine, the hydraulic control
system and the drive system that couples the turbine to the generator. These components are
detailed in the following paragraphs.
4.1.2.1 The inlet Valve
This valve regulates water before it reaches the turbine. It helps to stop the water
flow during maintenance and repairs without contributing too much to the head loss. The
inlet valves can be sluice valve, butterfly, and bi-plane types. However, the bi-plane valve
presents the advantages of being cheaper and introduces low head loss. Therefore, in this
study, it can be recommended to be applied to selected sites. The different characteristics of
these types of valves are summarized in Appendix 1.
4.1.2.2 The hydropower turbine
As presented in Section 2.1.3, the choice of the turbine depends on the head and flow
rate of water at which it is to operate as well as the efficiency, availability and cost of
maintenance. Regarding the available head and flow for selected sites, the reaction turbines
especially the Francis, Propeller and Kaplan are suitable for such a hydropower
development. However, the Francis turbine with its high efficiency of 94% can be
recommended for these selected rivers. With this assumption, in order to choose a suitable
turbine, Eq. (2.3) will be used to estimate the output power from the turbine. The estimation
will be done by assuming an efficiency of 94 % and taking the values of 𝑄 and 𝐻𝑛, which
are respectively the flow rate and the net head of the selected rivers. The calculated values
can help to choose the turbine in the market with the approaching size, that can be used for
the existing working conditions.
i.
Estimation of the rotational speed of the turbines
In order to estimate the rotational speed of the different turbines that can be used, the
calculation will be based on the formula proposer in [62].
58
𝑁 ∗ = 𝛼𝑄 ∗𝛽
(4.10)
Where, 𝑁 ∗ and 𝑄 ∗ are respectively the normalized rotational speed of the turbine and
the normalized flow rate of the water passing through the turbine; 𝛼 and 𝛽 are the fitting
constants. For small and medium hydropower plants, 𝛼 = 20.32 and 𝛽 = −0,36. From Eq.
(4.13), the left side can be written as follow:
𝑁
𝑁 ∗ = √2𝑔𝐻
(4.11)
𝑛
𝐻𝑛
Where, 𝑁 (𝑟𝑝𝑚) is the rotational speed of the turbine, 𝐻𝑛 is the net head and 𝑔 =
9.81 𝑚𝑠 −2 is the gravitational acceleration. It can be seen that in Eq. (4.14), the rotational
speed of the turbine was normalized by:
𝑇=
√2𝑔𝐻𝑛
𝐻𝑛
(4.12)
The term 𝑇 represents the inverse of the time employed by a fluid particle to flow freely
along the head difference 𝐻 [62].
Table 4-6: Estimated rotational speed for Francis turbines
Site name
Q*
N*
N [rpm]
[m³/s]
[rpm]
Loashi
21.2
13
0.001425
215
207.1
Mweso
29.1
10.2
0.000504
312.7
256.7
Lowa
49
8
0.000107
545.8
345.2
Talya Sud
198.8
3.57
0.000001
2571.3
807.9
kisalala
49.2
15.28
0.000203
433.5
273.8
Ibanda
49.2
15.9
0.000211
427.4
269.9
Kalundu
16.4
117.7
0.024332
77.4
84.6
Kanova
99.3
25.48
0.000059
678.5
301.6
Mahuma
39.4
63.71
0.001479
212.2
149.8
Semiliki 1
60.4
120
0.000955
248.4
141.6
Semiliki 2
60.4
120
0.000955
248.4
141.6
At the right-hand side of Eq. (4.13), the normalized flow rate can be calculated as follow:
𝑄∗ =
[m]
Q [m³/s]
𝑄
(4.13)
(√2𝑔𝐻𝑛 )𝐻𝑛2
This corresponds to the flow rate that would flow across a transversal section of an area 𝐻𝑛 2
(or a circular section of diameter 𝐻𝑛 , approximately) [62].
59
Using the aforementioned equations, the different speeds for selected sites can be estimated
as presented in Table 4-6.
Practically, the speed range of the Francis turbine varies from 75 to 1000 rpm [63].
Therefore, the values of 𝑁 as presented in Table 4-6 show that Francis turbine can be applied
on these selected hydro sites.
ii. Calculation of the output power of the turbine
By assuming an efficiency of 94% for hydro Francis turbines, the output power can
be derived as follow:
𝑃 = 9.81 × 𝑄 × 𝐻𝑛 × 𝜂𝑡
(4.14)
The results from Eq.(4.17) give the approximative values from which standard ratings of
turbines are selected The seller always specifies the type, efficiency, speed and all
characteristics of a turbine. Besides, he specifies the corresponding generator, governor and
valve that can be used with the turbine in question as presented in Appendix 2. The cost and
other details about these components can be found on the seller’s website [64] and [65].
iii. Unit capacity
The unit capacity as defined by the manufacturer may vary depending on the head
and the flow rate where it is supposed to operate.
Fig. 4-2: Typical Francis turbine performance: constant speed and full gate
60
A given per cent of the designed head and flow rate corresponds to a certain
efficiency and output power. For the case of the Francis turbine, Fig. 4-2 and Fig. 4-3 give
the specific characteristics that define its performance. Practically, the operation is
preferably restricted to a power range having an efficiency of 80 per cent or more [66].
Within the permissible range of head from 65 to 125 per cent of the design head, the available
power of the typical Francis unit will vary from approximately 45 per cent to 140 per cent
of the design power, unless limited by the capacity of the attached generator [66].
Fig. 4-3: Efficiency curve for Francis turbine
iv. Number of units
Generally, the determination of the number of turbines that need to be installed on a
given hydropower site is undertaken after the estimation of the total cost of the hydropower
scheme. The capital cost per kilowatt for a hydroelectric powerplant of a given capacity
generally decreases with a fewer number of units [66]. Multi-unit plants can efficiently meet
large variations of load by varying the number of units in service to ensure operation in the
high-efficiency range [66]. However, with modern systems, it is possible to operate a single
unit with high efficiency depending on the requirements given by the manufacturer. Singleunit plants may lead to lower operating and maintenance costs as they can operate with fewer
machines, but the larger equipment is likely to be more expensive. The number of units can
best be determined by a careful weighing of the foregoing limitations and criteria, rather
than by following a fixed rule [66].
61
4.1.2.3 Hydraulic Governor
In a power system, the connected loads vary from time to time. Moreover, in the case
of the hydropower plant, the water flow or head may vary depending on the season. These
facts disturb the speed of the turbine and the generator’s frequency. Thus the stability and
reliability of the electricity supply may be affected. Therefore, in order to keep the turbine
speed constant, a speed governor is used to regulate the guide vanes and needle vanes
according to the load. As per IEEE standard -75, the hydro turbine is supplied with some
components which constitute the governor system. These components include those that
control and sense the turbine’s speed, the hydraulic pressure, actuators, and servomotor
control systems. The followings are the main roles of a hydraulic governor [67]:
•
During synchronization with the grid, the hydraulic turbine helps to start, adjust and set
the generator’s speed.
•
After synchronization, the hydraulic governor adjusts the output of the turbine according
to the variation of the load.
•
When there is a fluctuation of the frequency on one generator, the governor facilitates
the sharing of load with the other generators in a planned manner
•
It adjusts the output of the unit in response to the operator or other supervisory
commands.
•
It can shut down the system in normal operation, or in case of an over speed emergency.
Fig. 4-4: Basic Governor Control System [67]
The governing system is composed of two main sections as can be seen in Fig.4-4: the
Control section (maybe mechanical; analogue electronic or digital electronic), and the
hydraulic actuation section. The hydraulic actuator can be Mechanical, a dummy load or a
hydraulically controlled actuator. The hydraulic actuators are mostly used in schemes of
rated power more than 1000𝑘𝑊 , whereas the load and mechanical actuators are used
62
respectively in micro-hydro schemes and 1000 𝑘𝑊 unit size range. Therefore hydraulic
actuators are suitable to be applied in the case of this study. The three main types of hydraulic
governors are mechanical, electrical and the dummy load governor. The dummy load is a
type of hydraulic governor that varies in response to variations in the external electrical load.
The dummy load-based governor is applied in small-scale hydropower plants.
i. Mechanical governors
The first generation of mechanical governors was coupled to the primer mover through
the belt. The rotational speed of these types of governors was sensed by fly-ball type
pendulum, unlike second-generation mechanical governors where permanent magnet
generators were used to sense their speed. These technics contributed to full and stable
control of the generator output and offered a possibility for manual control of the units with
handles and knobs in case of a faulty pendulum.
ii. Electrical governors
Two types of governors are classified in this category: Electro-Hydraulic Governors
based on analogue electronics and electro-hydraulic governors based on digital electronics
also referred to as Digital governors (or PID governor controllers). Introducing electrical
control systems, led to the third generation of hydraulic Governors where the speed sensing
and all the control mechanism were done without mechanical components. Thus the
reliability, stability and life of the equipment were increased and facilitated more functional
requirements. Moreover, the advancement in electronics led to the development of more
reliable governor controllers, starting from analogue electronics to digital electronics-based
governors. In the digital control system, the microcontroller is programmed to accomplish
the required control function. Thus the control system becomes very flexible (control
functions can easily be changed via software), stable, reduces wiring and easy remote control
and can accommodate self-diagnostic features. The following reasons justify the fact of
recommending the use of digital governor in this study:
•
Digital governor control systems can control the speed control during an operation in
idle mode,
•
They can facilitate a given generator to operate in the isolated grid network; in the
grid-connected system and in islanding operation.
•
They can easily deal with the load frequency control by adjusting the power output of
the generator.
63
•
They can assume the power control of several generating units in a power station
•
They control the power as per water levels in Forebay and/or Tailrace
•
A single command can automatically aloud the Starting or the Stopping of the system.
•
They have a fast response to transient conditions
•
They present a possibility of remote control via the Supervisory Control And Data
Acquisition (SCADA)
4.1.2.4 Drive System (Speed increaser)
The speed increaser couples the generator to the hydro turbine. This drive system
allows the turbine to spin at the velocity that delivers the correct voltage, frequency and best
efficiency [54]. There are four main types of drive systems which are: Direct coupling, belt
and pully coupling, chain and sprocket, and the Gearbox. Each of these drive systems
introduces additional efficiency losses into the system and has its advantages and
disadvantages. The type of the drive system is determined by the speed ratio between the
generator shafts and the turbine. The direct coupling system between the turbine and the
generator facilitates the operation at the same mechanical speed, thus it increases the system
efficiency, saves space in the hydro-power station, cancels the gear-box or pulley and belt,
limits the lubricant utilization in the hydro-power station and reduces the system cost [68].
The direct coupling system can be applied at some particular sites, whereas in AC systems,
other coupling systems can be used since it is necessary to adjust the transfer ratio so that
the turbine and the generator run at their respective optimum speeds [57]. In the case of a
lower power range, turbines run at less than 400 𝑟. 𝑝. 𝑚. Therefore, they require a speed
increaser to meet 1500 𝑟. 𝑝. 𝑚 of the standard alternator. In the range of small and microhydro schemes, the use of a speed increaser (gearbox) is more economic than the use of a
custom alternator. Belt systems tend to be more popular because of their lower cost and can
accommodate very large speed ratios with an efficiency of 95 − 98%, depending on the type
of belt [57]. Their only drawback is that their lifespan is short. On the other hand, the
Gearbox systems present a long life with an efficiency that varies between 95 % and 97 %,
but their cost is relatively high and they require maintenance. They are acceptable under
special circumstances only (high gearing ratio) [68]. In this study, the gearbox can be
recommended.
4.1.3 Electrical design
This section discusses all the electrical components of a hydropower grid-connected
system. Firstly, the selection of the generators that will operate with the hydro turbines for
64
selected hydro sites will be conducted. Secondly, the transmission of the electricity
generated will be discussed, followed by the presentation of the interconnection
requirements of a hydropower plant to the load and the grid. This will lead to the feasibility
study of the whole system and its design in Matlab/Simulink.
4.1.3.1 Generator
i. Choice of the type of the generator
As presented in Section 2.1.3, the two main types of AC generators which are used
in the hydroelectric scheme are Synchronous generators and Asynchronous generators
(Induction generators). Some criteria that determine the type of generator for a given
hydropower scheme are the maximum turbine power, the runaway speed of the turbine, the
horizontal or vertical construction, whether the isolated or parallel operation, constant load
or variable load, the Reactive power supply and the characteristics of the Grid in case of
Grid-connected operation [69].
Table 4-7: Pros and cons of using Synchronous and Induction Generators [70]
Both synchronous and induction generators can be used in Grid-connected systems,
but in the case of weak Grids, induction generators can not allow a continuous operation of
the power supply, since they need reactive power from the Grid for their operation.
Therefore, synchronous generators are suitable for standalone schemes (isolated networks),
65
as they can be applied as well in case of weak grids to ensure continuous power supply
during the failure of the Grid. The following points lead to the choice of the type of generator:
• Synchronous generators can be connected to any network since they regulate the
voltage at their terminals and can feed reactive power to the grid [70].
• The induction generator requires the use of a tachometer that couples it to the grid.
In a grid-connected system, it absorbs reactive power from the grid thus it causes a
transient voltage drop in the network. Therefore, it requires that the power factor be
improved by installing a capacitor bank. Moreover, the efficiency of an asynchronous
generator is generally lower than that of a synchronous one [70].
According to the aforementioned advantages of a synchronous generator over an induction
generator, and since the available Grid in North Kivu province, is not stable, the synchronous
generator is suitable in the case of this study. Therefore, the simulation of the Grid-connected
system will be based on the Simulink model of the synchronous generator. The comparison
of a synchronous and asynchronous generator is given in Table 4-7.
ii. Rating of the generator
The rating of the generator should correspond with the kW rating of the turbine and
the designed net head. However, the capacity of the generator should be able to support the
available turbine’s capacity at an opening gate of 90%, within the acceptable rated generator
temperature rise [70]. The output kVA of the generator depends considerably on the location
of the power plant from the load centre, the interconnected transmission system, the
anticipated load, the substations and distributed facilities involved in the system. All these
parameters affect the power factor of the generator which is generally between 0.8 and 1.0
for synchronous generators. Thus, taking into consideration the power factor, the rating of
the generator can be calculated as follow:
𝑃𝑔 (𝑘𝑉𝐴) =
9.8×𝐻×𝑄×𝜂
(4.15)
𝑝𝑓
Where, 𝑃𝑔 is the capacity of the generator (𝑘𝑉𝐴), 𝐻 is the net head (𝑚), 𝑄 is the rated
discharge (𝑚3 /𝑠), 𝜂 is the combined efficiency of the turbine and the generator (%) and 𝑝𝑓
is the power factor (%). Since the type and characteristics of a generator are determined by
the turbine, the proposed generators in Appendix 2 can be maintained. Their standard ratings
will be those proposed by the manufacturer. The specifications of the generator that are given
by the manufacturer include mainly the speed, connection of stator winding, the rated active
66
and reactive power, voltage, current, frequency, the number of phases and their sequences,
the 𝑐𝑜𝑠𝜑, the cooling method, the rise of the temperature, type of excitation and its voltage,
and the reactance of the windings of the machine.
iii. Generator terminal voltage
As per international standards, the recommended minimum voltage rating and
economical terminal voltage for small hydro generators are shown in Table 4-8. By
considering these aforementioned voltage standards, it can be seen that the sites Lowa,
Loashi and Mweso will be designed with a generator voltage rating of 6.6kV and the
remaining generators with 11kV, regarding their respective rating power. The use of these
standard voltages (6.6kV and 11kV) for the generation can ensure the economic aspect of
the energy generation and its feasibility. After generation, it will be required to step up this
voltage to the required voltage for transmission lines as it will be shown later in the following
sections.
Table 4-8: Recommended rated economical terminal voltages of the generators [70]
Minimum Voltage
3.3kV- Above 150kW (or kVA)
6.6 kV - Above 800kW (or kVA)
11kV - Above 2500 kW (or kVA)
Economical voltage
Up to 750 Kva - 415 volts
751 - 2500 kVA - 3.3 Kv
2501- 5000 kVAn- 6.6 Kv
Above 5000 kV - 11 Kv
iv. Speed (rpm)
The generator speed depends directly on the turbine chosen. In general, for a fixed
rating power, the lower the speed, the higher the physical size and cost of the generators.
This shows that the cost and the physical size of the generators vary inversely with their
rated speed. To aloud a low-speed generator to operate at its synchronous speed for a power
capacity less than 3𝑀𝑊, it should be coupled to a speed increaser. But for capacities above
3𝑀𝑊, the power plant can operate at turbine speed [70].
4.1.3.2 The excitation system
The exciter sets the output voltage of the generator and maintains it at a stable value
during the operation of the hydropower plant under different load conditions. [70]. For a
better operation of the excitation system, its voltage should not exceed 250𝑉 𝐷𝐶.
67
4.1.3.3 Transformer
Before transmitting the generated energy to the point of interconnection with the grid,
step-up transformers are used to increase the voltage up to the rated voltage of the grid. The
transformer contributes as well to reducing energy losses in long transmission lines. The
details about the transformers that will be used in this work are discussed in section 4.3.
4.1.3.4 Power transmission
The electricity generated is transferred from the powerhouse to the grid connection
point through power transmission cables. Cables are distinguished depending on their usage,
the level of the voltage, the form of the magnet field, and the material used for the isolation
of conductors. The transmission system may be, undergrounded or overhead lines depending
on the level of the voltage and the state of the area where it is supposed to pass. The
underground transmission lines are mostly used for voltage range greater than 1000𝑉 ,
whereas the overhead lines are preferred in medium and low voltage range. The choice of
the right side of the conductor has to be conducted concerning the following requirements:
•
The conductor should be able to carry the nominal current of the generator,
•
The conductor should aloud the protective equipment to protect the network against
overloads and short circuits.
•
It should not cause any excess voltage drop between its two ends as recommended by
standards in [35] and [71]. Table 4-9 gives the limits of voltage drop in the case of copper
conductors according to the sectional area.
Table 4-9: Voltage drop of multicore PVC insulated cables [57]
Conductor cross-section Three/Four core, three-phase AC
area [mm2]
copper [Mv/A/m]
1.5
29
2.5
18
4
11
6
7.3
10
4.4
16
2.8
The voltage drop over a certain length of the power transmission line can be found as follows
[57]:
𝑉𝑑 = 𝐶𝑣 𝐿𝑐𝑎𝑏𝑙𝑒 𝐼
(4.16)
68
Where 𝐶𝑣 is the voltage drop of the specific conductor size that can be found in Table 4-9,
𝐿𝑐𝑎𝑏𝑙𝑒 is the length of the cable and 𝐼 is the rated current of the generator that flows through
the cable. For distribution lines, at first, the voltage drop at the farthest point of utilization
has to be calculated. If the voltage drop in the transmission line is around 10%, a low voltage
line (400/220𝑉) can be used. However, if the voltage drop becomes more than 10%, an
11𝑘𝑉 line is required [68].
4.1.3.5 Interconnection with the Grid and Switchgear
Grid interconnection system has the advantage of more effective utilization of the
generated power through load sharing between interconnected generators. However, the
technical requirements from both the utility power system grid side and the distributed
generators need to be satisfied to ensure the safety and reliability of the energy supply.
i. General Grid interconnection requirements of hydropower plants
In this study, hydropower units will be connected to the grid as distributed generators.
These DGs will bring to the distribution level the improvement of the power capacity, the
expansion of the sources of power supply, and the reduction of the overall power production
costs. Thus, they will noticeably enhance the load factor and ensure the continuity of the
electric power supply in the system [68]. By interconnecting to the Grid, a new generator
has to demonstrate that when producing no net output, it would not put the transmission
system in danger of instability and that it would not cause fault currents (during short
circuits). The fault current should not exceed the capability of protective devices that
interrupt power flows and isolate the faulted portion of the system [72]. Practically, the
interconnection of a given generator to the existing network may require additional costs
related to the upgrade of the transmission system, so that the Grid can maintain reliability
standards after the addition of each new generation. A new generator is added within the
power balance between the load side and the generation side. The sum of the load, losses
and net export power should be in balance with the summation of the generation and the net
import power. Some different studies that differ in scope and details are performed before
interconnecting a given number of generators:
•
Firstly, the completed application for a specific interconnection is generally followed by
a feasibility study that provides preliminary information on the required transmission
system upgrades and associated costs, based on steady-state load flow and short circuit
analysis.
69
•
Secondly, an Impact Study is conducted to determine the transmission system
reinforcements needed through analyses based on the steady-state load flows, shortcircuit studies, and stability analyses [72].
•
Thirdly, a Facility Study is conducted. This provides details on required upgrades and a
more accurate cost estimate for necessary equipment additions during the
interconnection process.
Before any approval of a grid-connected system following requirements need to be met by
the generator owner:
• The owner has to submit to the existing Grid a complete site plan, detailing the physical
locations of all equipment including the location of proposed metering, disconnecting
and circuit protective devices, and provisions for grounding of the Generating Facility.
• The owner has to submit a one-line diagram of the system including all equipment
(installed or which will be installed), which states wire sizes and types, as well as
ratings and types of circuit protective devices that will intervene in the Grid connection
system.
• A relay control diagram which indicates relays contact arrangements, their operation,
protective devices and interlocks is required.
• The owner has to specify the location and the manufacturer’s data of the generating
facility, including the ratings, impedances, time constant, and all associated control
equipment, including the exciters, governors, voltage regulators and synchronizers,
where applicable.
• The ratings and switching arrangement for power factor correction capacitors, and
their location have to be known.
• Proposed operating procedures including all operational parameters and appropriate
limits of operation for startup, shutdown and restart functions have to be identified in
advance,
•
The monthly energy production and the anticipated peak power production have to be
specified as well.
The operation of hydropower plants in grid interconnected mode requires the following
features:
•
The power plants should agree on AC or DC grid-connected system, to ensure
compatibility between power plants.
70
•
In the case of an AC grid-connected system, the power plants have to operate at the
same frequency within acceptable limits of deviation.
•
The power plant should operate at its respective capacity (in MVA)
•
The interconnection voltage (in kV) of all DGs should be the same
•
The point of interconnection (POI) should be able to respond to the requirement of
the chosen system
•
The protection equipment should be able to ensure the safety of the generators,
users and the overall grid-connected system.
•
The grounding system should be strong enough to ensure the protection of the
electrical network
•
The system should be monitored and controlled to ensure that the operation is
within high standards and meets the power quality requirements
•
The metering system should be accurate for measuring different parameters in the
system.
In case of a disturbance caused by one generator that does not meet the interconnection
standards, the owner is subject to penalties which are defined depending on each country’s
standards.
ii. Other operating requirements
The grid interconnections between power systems face several risks associated with
their technical complexities and their different operating costs. Thus, to achieve their full
benefits, they should operate within synchronization requirements, which ensure their
technical compatibility and operational coordination [68]. For better operation without
mechanical stress shock inside the generator, and to avoid current and power fluctuation
effects, the grid connection has to ensure that the generator’s frequency is the same as the
grid frequency. Furthermore, the generator excitation potential and the grid voltage should
have the same amplitude, polarity and phase. If the unit frequency and grid frequency are
not equal, there will be relative motion between the unit and the grid's voltage phasor [33].
When operating in grid-connected mode, a suitable voltage and frequency control system
needs to be established between the Grid and the distributed generators. The voltage and
frequency may change gradually depending on some issues that may be encountered during
the operation of the grid-connected system. The major cause of the voltage and frequency
fluctuation in Grid-connected systems is the tripping of the tie line. When it happens, a
hydropower unit may be disconnected from the Grid and operate in island mode, or it can be
71
shut down automatically. During island mode, the output power of the hydropower becomes
unbalanced and the frequency fluctuates. These effects can be explained by the Swing
equation [73]:
𝐽
𝑑 2 𝛿𝑚
= 𝑇𝑎 = 𝑇𝑚 − 𝑇𝑒
𝑑𝑡 2
(4.17)
Where 𝐽 is the total moment of inertia of the rotor mass in 𝑘𝑔 − 𝑚2 ,
acceleration
𝑑 2 𝛿𝑚
𝑑𝑡 2
is the angular
(𝛿 = load angle), 𝑡 is the time in seconds (s), 𝑇𝑚 is the mechanical torque
supplied by the prime mover in N-m, 𝑇𝑒 is the electrical torque output of the alternator
in 𝑵 − 𝑚 and 𝑇𝑎 is the net accelerating torque, in 𝑵 − 𝑚.
By multiplying both sides of Eq.(4.20) by the angular velocity 𝜔, for notational purpose
𝜔𝑇 = 𝑃 this leads to Eq. (4.21):
𝐽𝜔
𝑑 2 𝛿𝑚
= 𝑃𝑚𝑖 − 𝑃𝑒𝑖
𝑑𝑡 2
(4.18)
Where the product 𝐽𝜔 = 𝑀 represents the inertia constant, 𝑃𝑚𝑖 and 𝑃𝑒𝑖 are respectively the
mechanical and electromagnetic power of the generating unit. It can be seen that the
unbalanced power 𝑃𝑚𝑖 − 𝑃𝑒𝑖 of the turbine changes at the same rate as the load angle. As
long as the turbine’s power is unbalanced (𝑃𝑚𝑖 − 𝑃𝑒𝑖 ≠ 0), the load angle increases with
time, thus the generator will lose the synchronism. Furthermore, the unbalanced power
system of the island hydropower unit (𝑃𝑚1 − 𝑃𝑒1 ≠ 0) as shown in Eq. (4.22) leads to a nonzero frequency difference (∆𝑓 ≠ 0) . This frequence difference varies slowly with the
duration ∆𝑡 of the island mode due to the hydropower unit inertia [31].
∆𝑓 =
(𝑃𝑚1 −𝑃𝑒1 )/𝑆ℎ𝑦𝑑𝑟𝑜
2𝐻ℎ𝑦𝑑𝑟𝑜
𝑓0 ∆𝑡
(4.19)
The value 𝑃𝑚1 from Eq. (4.22), is the motive power of all the generators of the island system
before the failure; 𝑃𝑒1 is the total electromagnetic power; ∆𝑡 is the island duration; 𝑓0 is the
system rated frequency; 𝑆ℎ𝑦𝑑𝑟𝑜 is the hydroelectric island system capacity; 𝐻ℎ𝑦𝑑𝑟𝑜 is the
inertia time constant of island hydropower.
The fact that the hydropower is disconnected from the grid may lead to load shading. Thus,
it affects the efficient utilization of the hydropower plant as well as the reliability of the
power supply. To optimize the power supply a quick reclose of the tie line after solving the
fault in the network is needed. Since the inertia of the hydropower slows down the change
of the voltage and frequency, the tripped switch can be quickly closed to continue supplying
72
the power to the grid. This function is included in the control system (governor) for a better
operation of a hydropower Grid-connected system. Following requirements must be met for
better control of a grid-connected hydropower system:
•
The governor must be equipped with automatic over-voltage and over-frequency
protection equipment, to protect the hydroelectric unit from excess speed and voltage
that may damage the unit equipment.
•
The over-voltage protection of the hydropower generator should be set at 1.5 times
the rated voltage of the network [31].
• The operation should be guaranteed by suitable equipment that adjusts the opening
degree of the guide vane to set the output power of the turbine.
• The required time to adjust the turbine is 10𝑠, whereas the time required for planned
or unplanned shutdown events is in minutes.
• According to the distributed energy grid-connected standard, the switching operation
condition of quick standby automatic switching-on is set at ∆𝑓 < ±0.5𝐻𝑧, ∆𝛿 ±
10°, ∆𝑈 < ±7%.
iii. Control panels
Different control technics are applied in a hydro system, namely: supervisory control,
operational control, and output control methods. Supervision control is all about continuous
supervision, remote continuous control and occasional control of the power plant. The
operational control deals with the manual control, one-man control and fully automatic
control of the hydropower plant, whereas, the output control deals with the dummy load
governor control for isolated Grid, discharge control, water level control and programmable
control. These control technics include as well synchronising equipment. The
synchronization technic can be done manually or automatically. It is done by controlling the
voltage, frequency and phase. The main functions of the control panel are: to read and
display the pressure gauge at the penstock, the voltage and current at the output of the
generator and dummy load, the frequency of the generator, the operating time, the total
output energy of the hydropower plant in kWh, etc. [60].
iv. Switchgear requirements
The switchgear is a set of circuit breakers, switches, relays, fuses, etc. that protect
the power system from harm during fault conditions to ensure maximum continuity of the
power supply. It can isolate as well as connect the hydropower plant from the load or grid
73
under both normal and abnormal working conditions. A circuit breaker can operate in both
normal and abnormal conditions without replacement, unlike a fuse which necessitates being
replaced once it has detected a fault in the network (Short-circuit for instance). This fact
makes the circuit breaker a widely preferable type of switchgear. Moreover, the fuse can not
interrupt a large fault that may happen in the network. Therefore, since a Grid-connected
system operates with high voltage, a circuit breaker (which can be a simple breaker or an
automatic one) is preferable for such an application. A good choice of switchgear brings up
to the network the following essential features:
•
It contributes to improving the reliability of the power system,
•
It ensures the continuity of the supply by isolating the faulty from the healthy section in
the network without affecting the operation of the healthy part.
•
It operates quickly when there is a sudden fault (short-circuit) in the network to stop its
spread into healthy parts such as generators, transformers and other equipment. Thus the
overall system is protected from a complete shutdown during operation.
•
Switchgear must make provision for manual control in other to aloud a manual operation
in case the automatic control fails.
•
The provision of some additional instruments such as an ammeter, voltmeter or voltage
transformer is necessary. This voltage transformer facilitates the connection of the
generator to the main switchboard or a separate instrument panel.
4.2 Pre-feasibility study and economic analysis of the system through RETScreen
Software
In this section, the pre-feasibility study will be conducted to estimate the financial
viability of the hydropower projects that need to be developed for a Grid-connected system.
The economic pre-feasibility analysis will be carried out with the RETScreen Expert
software. This software is a widespread energy project analysis tool that facilitates the
execution of pre-feasibility and feasibility analyses for both, available and non-available
hydrological data of rivers. For our case, the hydrological data of selected rivers that would
help to determine the flow duration curve have not yet been assessed. Fortunately,
RETSCreen provides three levels of analysis that can facilitate the analysis of any electric
project depending on the available data. The first level of analysis which is suitable for this
study helps to determine the total energy that a given scheme can export to the grid given
the capacity factor of the hydropower plant being studied. Since hydropower plants possess
a capacity factor that varies from 40 to around 95% depending on the water availability
74
(without regulation via storage dam), the capacity factors of the selected sites that have been
used in the software to calculate the total energy exported to the Grid, have been estimated
based on the climate data of the region given in RETSCreen expert software. The level 1
analysis provides as well the economic analysis that helps the designer to know about the
initial capital cost of the scheme, its operation and maintenance Cost (O&M cost), and the
Levelized Cost of the electricity (LCOE), without taking into account taxes. It helps as well
to estimate the internal rate of return (IRR), the benefice cost ratio (BCR) as well as the
equity payback period (PBP), using empirical formulation as presented in section 2.1.6. The
outcomes of this Level 1 analysis, though they do not take into account a lot of details
relating to the hydropower site being studied, they present a pre-feasibility analysis that can
help to identify whether a hydropower project is economically feasible or not. For more
accurate analysis, it is required hydrological data to be collected during an onsite survey and
other details such as the cost of site components. The characteristics of the rivers have to be
involved as well in the feasibility analysis of the hydropower project before its
implementation. Such analysis is carried out in Levels 2 and 3 of RESTCreen. This will not
be part of this work since it would require more data that are not available. The analysis has
been conducted using standard input data available in RETSCreen, and some others that
have been customized to the context of the hydropower project and the country.
Table 4-10: Economic analysis of selected sites
Those inputs are the inflation rate (5%) , Debt interest rate (5%) , Debt term
(20 𝑦𝑒𝑎𝑟𝑠) and an electricity export escalation rate of 2.5%. Furthermore, a project life of
40 years was considered since hydroelectric power plants can operate with a life span
varying between 30 to 80 years without major overhauls. The results of the analysis from
75
RETSCreen as displayed in Table 4-10, show very attractive economic indicators, such as a
mean of 4,05 𝑦𝑒𝑎𝑟𝑠 payback period, a mean internal rate of return of 28.74%, an average
benefit-cost ratio of 4,08 %, and an average LCOE of around 0,08 𝑈𝑆𝐷/𝑘𝑊ℎ without
taxes. This cost approaches the one for the National Grid SNEL which possesses an average
electricity cost of 0.087 𝑈𝑆𝐷/𝑘𝑊ℎ for households [74]. However, it is less than the ones
of the other existing utilities in the province such as VIRUNGA Sarl and NURU society,
with their respective cost of electricity of 0,215 𝑈𝑆𝐷/𝑘𝑊ℎ and 0,415 𝑈𝑆𝐷/𝑘𝑊ℎ without
taxes. Therefore, the results of this pre-feasibility study prove that hydropower development
in North Kivu province is cost-effective. Thus it can be recommended for investors who
would like to undertake such a project for the development of this province.
4.3 Simulation of the system in MATLAB/SIMULINK
In this section, the proposed Grid-connected system of the selected hydropower
plants will be simulated in Matlab software.
Fig. 4-5: Single-line diagram of the proposed system
A total of 11 hydropower plants grouped in four sub-systems which are: BENI, LUBERO,
MASISI and WALIKALE, will be connected to the Grid. Fig.4-5 presents a schematic
diagram of the proposed Grid-connected system. The existing Grid consists of a 70kV
transmission line that comes from the RUZIZI hydropower plant located in the South Kivu
province. In order to interconnect with this Grid, the generated electric power from different
locations will pass through step-up transformers in order to reduce losses in transmission
76
lines. This study will be based on the load flow analysis to see how electrical power is shared
between different buses without more details on control and power quality. Thus the active
power and the frequency that will be analyzed at different buses will constitute the core
elements for future works and recommendations in order to improve the proposed system
before its implementation.
4.3.1 Simulation process in MATLAB/Simulink
The simulation will be done using block models that can be found in the Simulink
library. The operation and control of a single hydropower plant can be summarized by the
block diagram in Fig.4-6.
Fig. 4-6: Block diagram of the hydropower plant [25]
Each block in the above diagram can be represented by its Simulink model. This
facilitates the setting of different parameters of the hydropower sites in different blocks. The
mathematical modelling of these blocks can be found in [25]. The function of these blocks
in the circuit is presented in the following section.
4.3.1.1 Simulink blocks
The Simulink blocs that will intervene in the proposed system and their main inputs
are as follow:
• Three-phase source: This bloc implements a three-phase source with internal R-L
impedance. It will be used here as the main Grid, where all generators will be
connected.
•
Synchronous generator: This bloc represents the dynamic model of a three-phase
salient-pole synchronous machine. The main inputs that have been introduced in this
block are the nominal apparent power (VA), voltage (Vrms) and the frequency (Hz)
of the synchronous generator. Other parameters have been kept at their default
values.
77
•
Hydropower turbine and governor bloc: this bloc integrates the turbine model and
the proportional-Integral-Derivative (PID) governor system which helps to regulate
the output power of the synchronous generator by adjusting the gate of the turbine.
•
Excitation block: this bloc represents a DC exciter for the synchronous generator and
regulates its terminal voltage in generating mode. Its parameters are set automatically
by the powergui bloc during the initialization of the model.
•
Powergui block: This block provides methods that help to solve the designed circuit.
These methods can either be continuous (which uses a variable-step solver from
Simulink), Discretization of the electrical system for a solution at fixed time-steps,
or Phasor solution. The powergui bloc is needed when simulating any Simulink
model containing blocs from Simscape/power systems/Specialized technology
blocks. The continuous method has been used in this study to facilitate the load flow
analysis of the designed Grid-connected system. The state-space equations of the
Simulink model are stored automatically in the powergui block, during its
initialization. For the optimal operation of the powergui block, it must be placed in
the top-level diagram, and it should be named “powergui”.
•
Three-phase transformer bloc: it implements a three-phase transformer using three
single-phase transformers. It can be used as a step-up transformer or a step-down
transformer.
•
Distributed parameter line: This bloc implements an N-phases distributed parameter
line model.
•
The three-phase VI measurement: It can be used to measure three-phase currents and
voltages in the circuit or as a bus.
•
Scope: It helps to display the signal generated during simulation.
•
Bus selector: It is used to select a signal from the incoming bus.
•
Three-phase parallel RLC load block: It implements a three-phase balanced load as
a parallel combination of RLC elements. At the specified frequency, the load exhibits
a constant impedance.
By interconnecting the aforementioned blocks, a hydropower plant model with a
synchronous generator is shown in Fig.4-7. For a large model containing many blocks, it can
be advisable to use subsystem blocks, where a group of blocks are gathered in a single block
to simplify the circuit. In this work, subsystems will be used to represent each substation.
78
Fig. 4-7: Hydropower plant model
4.3.1.2 Input configuration for the simulation
The input parameters that are required in each block of the synchronous generator to
define the different hydropower plants are the rating output power (kW), the phase-to-phase
voltage (6.6kV or 11kV), the operating frequency (50Hz), and the rating apparent power
(VA). Since the study will consist of the load flow analysis of more than two power sources,
especially synchronous generators, it is recommended to set all sources as swing (slack)
buses. The solver can be maintained at “auto” to let Matlab decides on which suitable solver
to use during the simulation. The simulation time will be set to 0.04s as it is recommended
by the sampling principle (frequency of the signal 50Hz). Since the electric power will be
produced from remote areas, it will be transmitted over large distances with the help of
transmission lines. Therefore, in order to maintain transmission efficiency, save the
conductor materials and reduce losses due to long transmission lines, step-up transformers
are required. Practically, it is advisable to increase the voltage to the highest possible voltage
(66kV, 132kV, 220kV or 400kV) during transmission of the electric power. But since a high
voltage in the transmission line induces a high cost of different elements of the network,
there is a need to choose an optimum voltage at which the produced electricity can be
transmitted economically. Thus, as per American standards, the economical transmission
voltage can be found in Eq. (4.23).
79
Table 4-11: Voltage of the transmission lines
Site name
Capacity
[Kw]
Kisalala
Ibanda
Mahuma
Semiliki 1
Semiliki 2
Lowa
Talya Sud
Kanova
Loashi
Mweso
Kalundu
7500
7800
25000
72000
72000
3900
7000
25000
2800
3000
20000
Territory
Generator
Distance
voltage
from the
(kV)
GRID (km)
BENI
11
250
BENI
11
250
BENI
11
250
BENI
11
253
BENI
11
253
LUBERO
6.6
210
LUBERO
11
210
LUBERO
11
210
MASISI
6.6
220
MASISI
6.6
220
WALIKALE
11
200
𝑉 = 5.5√0.62 𝐿 +
Economic
Voltage
(kV)
95
96
140
219
219
79
90
138
75
76
125
3𝑃
150
(4.20)
Where 𝑉 is the line voltage in 𝑘𝑉, 𝑃 is the maximum 𝑘𝑊 per phase and 𝐿 is the
length of the transmission line in 𝑘𝑚.
Fig. 4-8: Simulink diagram of the Grid-connected system
It can be seen that the economical transmission voltage depends on the distance from the
Grid and the power that needs to be transported. The calculated voltage of the transmission
lines and the distance of the selected hydropower plants towards the main Grid are given in
80
Table 4-11. The highest calculated economical transmission voltage approaches 220 kV.
Therefore, for simplicity, all the transmission lines will be rated at this value. At the PCC
with the Grid, the received voltage will be stepped down from 220 kV to 70 kV. From there,
the electric power can be conveyed through a distribution network via feeders to supply
electricity to small and big consumers connected to different small-size transformers. Other
parameters of the transmission lines (the per unit length resistance, inductance and
capacitance) will be maintained at their default values as proposed by Matlab. The
parameters of the hydraulic and governor as well as for the excitation will be adjusted by the
powergui block during the initialization of the model. The overall model of the hydropower
Grid-connected system is shown in Fig.4-8.
4.3.2 Results and discussion
The study of this power system is based on load flow analysis where active and
reactive power shared between different buses will be determined. Besides, the voltage and
the phase angle at each bus will be calculated. Lastly, the frequency of the analysis of the
whole system will be conducted. The closed-loop system of the synchronous generator as
presented in Figu.4-8 ensures the automatic load frequency control of the system.
4.3.2.1 Analysis of the active and reactive power shared in the electric network
The simulation will be done by taking into consideration the fact that, the total
generated power has to be equal to the total electricity demand. Since the total hydropower
capacity for major hydropower plants that were chosen is equal to 246𝑀𝑊, the Grid is
supposed to provide 4.15𝑀𝑊 to cover a total demand of 250.15𝑀𝑊 . The load flow
analysis will give the total active and reactive power that will be generated according to the
location of the chosen hydropower plants, and their different configurations. Table 4-12
presents a summary of the load flow analysis of the proposed Grid-connected system.
Table 4-12: Summary of the load flow analysis
Total generation
Total PQ load
Total Z shunt
Total losses
P(MW) Q(Mvar)
250.15
-128.14
45
-0.02053
199.15
30.72
5.99
-158.83
The total active and reactive power which is being shared between buses is
respectively 250.15𝑀𝑊 and −128.14𝑀𝑣𝑎𝑟 . It can be seen as well that a total of
244.15𝑀𝑊 (made of PQ load types and Z shunt) over a total generated of 250.15MW is
81
supplied to the load, whereas, around 2% (5.99𝑀𝑊) of the generated power is lost in the
network. This proves that the proposed Grid-connected system requires improvement to
reduce losses by installing suitable compensators for reactive power balance in the network.
A voltage and power report for each bus is presented below. On one side Table 4.13
presents the load flow results at different buses where all synchronous generators and the
Grid are connected. On the other side, Table 4.14 presents the load flow results of buses
where different PQ loads and Z-type loads are connected. These loads were fixed randomly
for simulation and analysis. From Table 4-13, the active and reactive powers which are being
generated by different sources are presented. At each generator bus (in Yellow colour) the
voltage and angle are computed. The results show as well the active and reactive power
which is being consumed by different loads connected to the concerned bus. These loads are
PQ and Z-type loads. The blue columns show respectively the active and reactive power,
that the concerned bus shares with neighbour buses. Generally, generation buses are referred
to as PV buses in load flow analysis. However, when two or more generators are
interconnected, one should be set as a “Swing bus “ (slack Bus). This study is the case where
many generators can be set as a “Swing bus” to balance the power in the system proposed.
This can be seen in Table 4.13, where buses 57; 59; 62; 74 and 75 are considered swing
buses. It is recommended to choose the bus where a generator with a high power rating is
connected. For our case, the hydropower stations which have been set as swing buses are
Mahuma, Semiliki1 &2, Kanova and Kalungu. The negative reactive power at the generation
buses shows that the synchronous generators connected to the Grid are under-excited, thus
they consume reactive power from the Utility Grid. To correct this, the excitation voltage
should be increased or it should be required to install a capacity bank at each bus for reactive
power balance. Moreover, the analysis presented in Table 4-14 shows how active and
reactive power is being absorbed by PQ and Z-type loads and how they are transmitted to
neighbour buses connected through lines, series impedances and transformers. The yellow
columns represent the main buses where other buses take their energy. Their voltage and
angle are displayed accordingly. Such analysis is useful in the planning and execution of a
power system since it shows how the system can operate under given working conditions.
The other parameter that needs to be analyzed is the frequency of generators in a Gridconnected system. This is presented in the following section.
82
Table 4-13: Load flow analysis at generation buses
83
Table 4-14: Active and reactive power absorbed by PQ and Z-type loads
Legend
84
4.3.2.2 Frequency analysis
During the operation of a power plant, when loads increase or decrease the frequency
decreases or increases accordingly. In order to adjust the frequency, the automatic load
frequency control loop, which comprises a generator, load, prime mover and governor is
used [75]. The frequency analysis at different buses where synchronous generators are
connected is presented in Table 4-15.
Table 4-15: Measurement of frequency at generation Buses
Site name
Bus
Min Freq. (Hz)
Max freq. (Hz)
Kisalala
Semiliki 1
Loashi
Kanova
Semiliki 2
Mahuma
Ibanda
Mweso
Talya Sud
Lowa
Kalungu
72
75
64
59
74
70
68
66
61
56
57
49.997
49.92
50
50
49.88
50
50
50
50
50
49.78
50
50
50
50.25
50
50
50
50
50
50
50
Average freq.
(Hz)
50,0
50,0
50,0
50.1
49.9
50,0
50,0
50,0
50,0
50,0
49.9
Average freq. (Hz)
50.2
50.1
50.1
50.0
50.0
49.9
49.9
49.8
49.8
Fig. 4-9: Variation of the overall frequency of the system
It can be seen from Fig. 4-9 that the system is in general stable on the loads that were
taken into consideration during simulation because the deviation of the frequency is less than
±5𝐻𝑧 as it is recommended by standards. This is due to the PID controller included in the
Governor. It strives to stabilize the generator to the Grid for a suitable working condition.
Thus the designed system can be proposed since it operates in conditions that are not far
from the standard operation of Grid-connected power systems.
85
5.
Chapter 5. CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion
In this study, the aim was to assess the hydropower potential of rivers in the NorthKivu province and to design a Grid-connected system for major hydropower plants in order
to enhance the reliability of the electricity supply in the region. The incentive behind this
research was to prove the hypothesis highlighted in the main introduction which are:
•
The electricity demand of the North-Kivu province can be exploited economically
by promoting hydropower plants in each of its territories;
• The reliability of the electricity supply in the province can be enhanced by an
interconnected system of hydropower plants.
The analysis presented was based on existing data from the Atlas of renewable energies of
DRC 2014 Version, and was facilitated by relevant literature that have been referenced in
this work. Moreover, regarding the hydro energy potential of the province, there is no
database of recorded flow duration curves of rivers in the province and other relevant details
of the identified rivers that would intervene in the economic study of the hydropower
projects in the region. Due to this reason, data obtained from the RETSCreen Expert software
database were used to conduct the pre-feasibility study of the proposed system.
Matlab/Simulink software was used for the simulation and the load flow analysis of the
resigned Grid-connected system.
The collected data of rivers from hydrological maps of each territory of the province
led to a total of 95 hydropower sites, classified in terms of Micro-hydropower (13 −
88𝑘𝑊), Mini-hydropower (100 − 915𝑘𝑊), Small hydropower plants (1 𝑡𝑜 7.8𝑀𝑊) and
Medium hydropower plants (20 − 72𝑀𝑊) . This showed that there is a wide range of
hydropower development in the province (off-Grid, Mini-Grid and Grid-connected
Systems). The total hydropower potential of around 359.07𝑀𝑊 has been evaluated through
rivers located in each territory of the province. It has been found that this potential can cover
43.2% of the actual electricity demand of the province evaluated at around 831.4𝑀𝑊.
By taking into consideration the facts that the residential loads increase by an annual
rate of 8.2% and 5.2% for industrial loads (Commercial, small and medium industries), the
load forecasting of the province, 10 years ahead showed an important increase of the actual
electricity demand by 716.9𝑀𝑊. In order to cover the actual and future demand, it has been
86
shown that other resources available in the province such as natural Gaz, Geothermal, solar,
etc. have to be exploited.
Furthermore, a Level 1 pre-feasibility study of a Grid-connected system composed
of major hydropower plants of the region has been conducted in RETSCreen Expert
software. The analysis took into consideration inflation and a debt rate of 5%, a debt term of
20 years, an electricity export escalation of 2.5% and a project life of 40 years. The results
led to very attractive economic indicators such as an average of 4.05 years of PBP, 28.74%
of IRR, 4.08% of BCR and a LCOE of around 0.08𝑈𝑆𝐷/𝑘𝑊ℎ without counting taxes. This
cost of electricity was found affordable comparatively to the one for existing utilities in the
province (Main Grid SNEL 0.087 𝑈𝑆𝐷/𝑘𝑊ℎ for households, Virunga Sarl 0.215 𝑈𝑆𝐷/
𝑘𝑊ℎ and Nuru company 0.415 𝑈𝑆𝐷/𝑘𝑊ℎ).
Lastly, the simulation of the proposed Grid-connected system composed of 11
hydropower plants has been conducted using Matlab/Simulink block models. The network
was grouped into four subsystems to ease the interconnection. The load flow analysis of the
system showed that, with a total of 250.15𝑀𝑊 generated from different generation buses,
5.99𝑀𝑊 was lost in the network. This proved that the proposed system needs more
improvement but constitutes the basic stage for future work in this area.
5.2 Recommendations
The recommendations made out of this study are on one side directed to future works,
and on the other side directed to decision-makers. Existing studies on the energy potential
of the North-Kivu province in the DRC have revealed numerous hydropower sites which
remain unexploited. The studies have been limited to the identification of the hydro site
without evaluating to which extent this potential can contribute to the electricity supply in
the province. Furthermore, with the actual low rate of access to electricity in the province,
the studies did not provide any technical solution that would contribute to increasing the
actual electricity rate access and enhancing the reliability of the electricity supply. In this
age where interest is oriented toward Smart Grid technology for the improvement of the
reliability of the electricity supply, Off-Grid systems and Grid-connected systems for the
province would serve as the pilot of this trend. Therefore, it can be recommended to the
government, non-governmental organizations and private sectors give due attention to this
work in the following key elements:
•
The available hydropower potential as assessed in the province can be harvested
through different technologies such as Pico, Micro, Small and Mini hydropower
87
plants. This constitutes a huge opportunity for private and public investors, and an
interesting area for future research for the development of such projects in the
province.
•
It can be recommended to future researchers to undertake a physical assessment of
all identified hydropower sites, measure the hydrological data of all rivers, take into
consideration all geological characteristics of the sites and evaluate the cost of all
hydropower components based on the country’s standards. This would lead to an
accurate feasibility study through a Level 3 analysis in RTSCreen Expert software,
and it would motivate the concerned body to invest in this area for the development
of the project.
•
This study focussed on the hydropower potential assessment of rivers in the NorthKivu province. However, since the province possesses other resources assessed and
unassessed, other researchers interested in this area should study how these resources
can be harvested to cover the actual and future electricity demand of the province.
Thus a hybrid Grid-connected system shall be implemented in the province to
increase the electricity rate access of the province.
•
The Load flow analysis can be done to verify the stability and power quality of the
system proposed Grid-connected system.
88
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7.
A. APPENDICES
Appendix 1: Types of valve
Table A-1: Types and characteristics of each type of Inlet Valve
Type
Butterfly Valve
Bi-plane valve
Sluice Valve
General
feature
Condition of Head: Not exceeding 200m
Diameter: Medium
application
(up to 2500mm)
Head loss is very high due to friction of the vane body
located in the centre of the valve (water pass), Leakage
Special
at complete closing is more than that of other types of
feature
valves. However, small-diameter valves are used widely
in the market due to cheap cost, good space factor and
simple construction.
Head loss
Medium
Leakage
Medium
Construction simple
Maintenance Easy
Cost
Medium
Head: Not exceeding 350m
Diameter: More than 500mm
Head: Exceeding 200m
Diameter: Small up to 500mm
The size of the servomotor becomes
Bi-plane construction is adopted to larger for large diameters, Vertical space
the vane body of the butterfly becomes higher, Product becomes
valve. So, water pass is enlarged heavier. Head loss is very small.
and head loss is decreased
Leakage at complete closing is very
small
Litle
Almost Zero
Litle
Very less
simple
simple
Easy
a little hard
Small diameter: A little costly /
High cost
Large diameter: Cheaper
94
Appendix 2: Selection of the turbine and the corresponding components
Table A-2: Choice of turbines and related components as per standard
95