SOLAR THERMAL ENERGY USE AS A SUBSTITUTE FOR
RESIDENTIAL BUILDING IN ETHIOPIA
A Thesis
Presented to the faculty of the Department of Mechanical Engineering
California State University, Sacramento
Submitted in partial satisfaction of
the requirements for the degree of
MASTER OF SCIENCE
in
Mechanical Engineering
by
Adnan Ahmed Bedri
SPRING
2013
© 2013
Adnan Ahmed Bedri
ALL RIGHTS RESERVED
ii
SOLAR THERMAL ENERGY USE AS A SUBSTITUTE FOR
RESIDENTIAL BUILDING IN ETHIOPIA
A Thesis
by
Adnan Ahmed Bedri
Approved by:
__________________________________, Committee Chair
Timothy Marbach, PhD
__________________________________, Second Reader
Dongmei Zhou, PhD
____________________________
Date
iii
Student: Adnan Ahmed Bedri
I certify that this student has met the requirements for format contained in the University format
manual, and that this thesis is suitable for shelving in the Library and credit is to be awarded for
the thesis.
__________________________, Graduate Coordinator ___________________
Akihiko Kumagai, PhD
Date
Department of Mechanical Engineering
iv
Abstract
of
SOLAR THERMAL ENERGY USE AS A SUBSTITUTE FOR
RESIDENTIAL BUILDING ETHIOPIA
by
Adnan Ahmed Bedri
Although electricity generation is steadily increasing in Ethiopia, a bias between the grid
extension and the load of power generated resulted in shortage of electricity and thus frequent
power cut. Limited electricity service makes the reliable power supply in isolated system more
attractive. The use of renewable energy and particularly the solar thermal energy represents one
of the most promising alternative strategies. Ethiopia is in a relatively sunny area with an average
global horizontal radiation of 5.2kwh per meter squares a day and 6.25kwh per meter square a
day in Diredawa. The residential sector represents 87% of the total energy consumption and thus
offers an interesting opportunity for the development of solar thermal market. In this paper an
attempt is made to examine and explore the impact of the use of solar thermal equipment for
heating and hot water on an energy saving and as substitute in the residential sector considering
Diredawa city as a model. The energy consumption is calculated for the typical building using
validated polysun solar thermal simulation model. Two model systems are considered, one in
which only solar thermal is used to supply energy demand but there is no energy savings. In the
second model, heat pump is coupled with solar thermal.
v
The system not only covered the energy demand but also showed the maximum energy savings of
3857.2Mcal. The payback period is calculated for heating and hot water for model system one is
4 years. The analysis showed that the payback period of the system is 3 years for the second
model of the system.
_______________________, Committee Chair
Timothy Marbach, PhD
_______________________
Date
vi
ACKNOWLEDGEMENTS
.
First of all, I would like to thank my thesis advisor Dr Timothy Marbach for his expertise in
renewable energy and thermal science advice throughout my study. Next, I wish to thank Dr
Dongmei Zhou, the second reader of my thesis for all her invaluable comments. Last, but not
least, I thank my family and my brother, Abdulaziz Bedri, for his great support and
encouragement.
I wish to express my gratitude to Vela Solaris and Polysun for releasing their simulation
program for free.
vii
TABLE OF CONTENTS
Page
Acknowledgements.........................................................................................................................vii
List of Tables……………………………………………………………………………………...x
List of Figures…………………………………………………………………………………….xi
Chapter
1. INTRODUCTION……………………………………………………………………………. 1
1.1 General overview……………………………………………………………………...1
1.2 Motivation……………………………………………………………………………..2
1.3 Statement of the problem……………………………………………………………..3
1.4 Objective of the study………………………………………………………………...4
2. BACKGROUND OF THE STUDY ……………………………………………………………6
2.1 Introduction …………………………………………………………………………..6
2.2 Analysis of energy context …………………………………………………………...7
2.3 Current status of solar thermal market and challenge ………………………………13
3. REVIEW ON SOLAR THERMAL ENERGY SYSTEMS ………………………………….16
3.1 Solar energy ………………………………………………………………………...16
3.2 Solar thermal use …………………………………………………………………...16
3.2.1 Solar water heating …………………………………………………………...16
3.2.2 Solar thermal for heating, cooling and ventilation ……………………….......17
3.3 Solar thermal collectors and energy analysis ………………………………………..17
3.3.1 Solar collectors ……………………………………………………………….17
3.3.2 Stationary solar collectors ……………………………………………………18
viii
3.3.2.1 Flat plate collectors…………………………………………….….....18
3.3.2.2 Compound parabolic collectors……………………………………...20
3.3.2.3 Evacuated tube collectors…................................................................21
3.4. Thermal analysis of flat plate collector…………………………………. ….....22
3.4.1 Flat Plate collector performance…........................................................22
3.4.2 Thermal efficiency of flat plate collector…………………………......23
4. DATA COLLECTION AND MODELING………………………………….……………… 25
4.1 Diredawa city specifications…………………………………………………..............25
4.1.1 Population size………………………………………………………………..25
4.1.2 Climate and geographic location…………………………………………......25
4.1.3 Residential building types………………………………………………….....26
4.2 Modeling and Simulation…………………………………………………………….. 27
4.2.1 Introduction……………………………………………………………………...27
4.2.2 Simulation data……………………………………………………………….. ..28
5. ANALYSIS OF SIMULATION ……………………………………………………………..31
5.1 Result ………………………………………………………………………………...31
5.2 Discussion...…………………………………………………………..........................48
6. CONCLUSION AND FUTURE WORK …………………………………………………...50
6.1 Conclusion …………………………………………………………………………...50
6.2 Future work and recommendation ………………………………………………….. 51
Bibliography …………………………………………………………………………………….52
ix
LIST OF TABLES
Tables
Page
1.1
Ethiopia electric power tariff ……………………………………………………………..4
2.1
World Bank Indicator- Ethiopia energy production and use ……………………………12
5.1
System overview (annual values)………………………………………………………..32
5.2
Meteorological data overview …………………………………………………………...32
5.3
Overview solar thermal energy (annual values) ……………………………...................33
5.4
Overview heat pump (annual values) …………………………………………………..33
5.5
Component overview (annual values)…………………………………………………..34
5.6
Solar loop …………………………………………………………………….................35
5.7
Total system report of solar thermal ………………………………………....................37
5.8
Financial analysis of solar thermal system …………………………………..................39
5.9
System overview (annual values) ……………………………………………………....40
5.10
Overview solar thermal energy (annual values) ………………………….......................41
5.11
Overview heat pump (annual values) ……………………………………………………41
5.12
Component overview (annual values) …………………………………………………..42
5.13
Solar loop ………………………………………………………………………………..44
5.14
Total system report-solar thermal and heat pump ………………………........................46
5.15
Financial analysis- solar thermal and heat pump ………………………………………..47
x
LIST OF FIGURES
Figures
Page
2.1
Share of Ethiopia’s energy supply 2008(%)………………….…………………………...8
2.2
Electric power consumption per-capita in Ethiopia ……………………………………..10
2.3
Development of energy generation of EEPCo ………………………………..................11
2.4
Electricity production from hydroelectric sources ………………………………............11
3.1
Pictorial view of flat plate collector. ………….…………………………….. …………19
3.2
Schematic diagram of a compound parabolic collector …………………………………21
3.3
Schematic diagram of a evacuated tube collector ………………………….....................22
3.4
Efficiency of stationary solar collectors……………………………………….................23
3.5
Thermal efficiency of flat plate solar collector …………………………………………24
4.1
Global horizontal solar radiation of Ethiopia ……………………………………………26
5.1
System diagram (solar thermal only) ………………………………………………........31
5.2
Solar thermal energy to the system[Mcal] …………………………………………........36
5.3
Total fuel and/or electrical energy consumption of the system [Mcal]…………….........36
5.4
Horizontal line of the sun ………………………………………………………………..38
5.5
Collector daily maximum temperature [˚F] ……………………………………………..38
5.6
System diagram (heat pump and solar thermal) ………………………………………...40
5.7
Solar thermal energy to the system [Mcal] ………………………………………….......44
5.8
Fraction of solar energy to the system (%)………………………………………............45
5.9
Heat generation energy to the system [Mcal]……………………………………………45
5.10
Total fuel and/or electrical energy consumption of the system [Mcal] ……………........46
5.11
Collector daily maximum temperature of model two[ ˚F]……………………………….48
xi
1
Chapter 1
INTRODUCTION
1.1 General overview
In recent years, a good deal of attention has been paid to research and development in
various fields of energy e.g. fossil fuels, nuclear energy, solar energy and etc. In particular a lot of
research has been done in solar energy in developed countries, while less is done in
underdeveloped ones, most of which have an abundant supply of solar energy are still striving to
follow suit. [1, 3, 11] As a developing nation, Ethiopia is rapidly increasing its energy
consumption and is short on energy supply. Fortunately, Ethiopia in particular the city of
Diredawa is located in that part of the world where the sun shines for maximum number of hours.
It is therefore a matter of interest to assess the significance of solar thermal energy and its
utilization in different fields of applications.
There are two main components of radiation reaching the ground: direct radiation and
diffuse radiation. In most energy application the global (or total) solar radiation on horizontal
surface is all that is required. However, in other application knowledge of diffuse radiation is also
essential. [3, 7]
In any solar energy conversion system, the knowledge of global solar radiation is essential
in the prediction, study and design of the economic viability of the system which use solar
energy. Information on global solar radiation received at any site (preferably gained over a long
period of time) is useful not only to the locality where the radiation data is collected, but also for
the wider community.
The use of solar energy equipment in residential building can play a significant part in tackling
the power deficit and environmental challenges. Indeed, because of the abundance of its sunny
2
days, the solar energy represents an important alternative for heating, cooling and ventilation.
Some research works have been conducted during the last few years to study renewable energy
market in Ethiopia but they focused on the geothermal energy for domestic hot water and
electricity. Thus there is a lack of information concerning the use of solar thermal energy for
space heating, cooling and ventilation. And also there is a need to evaluate the performance of
solar thermal equipment for this application for Ethiopian climate area what opportunities are
available.
It seems appropriate to look at the residential sector for two reasons: first it is an important
energy-consuming sector, and second it is the most promising sector in terms of development and
simple startup application. [3, 5]
1.2 Motivation
Energy is the primary and most universal measure of all kinds of work by human being
and nature. Everything in the world is the expression of flow of energy in one of its forms. [7, 11]
Energy is an important input in all sector of any country’s economy. The standard of
livening of any given country can be directly related to per capita energy consumption. Energy
crisis is due to the rapid growth of world population and the improved standard of living of
human beings. The per capita energy consumption is a measure of the per capita income or it is a
measure of the prosperity of the nation. [3]
Developing countries like Ethiopia are facing a critical power shortage as part of the
ongoing fast economic development activity noted in the country. Currently, the use of solar
energy source is seriously constrained by low efficiency of solar cells. Additionally, the high cost
of high intensity solar cells limits the use of solar energy to developing countries. A number of
research activities on alternative solar cells from cheap polymer material are undertaking. The
findings are indicative of possible cheap solar cell production in the near future. Therefore, the
3
use of solar energy for small scale domestic use in urban and rural area is an alternative future
direction and possibility. [3]
On the basis of these trends, there is a need to assess potential use of solar energy and
available solar thermal energy budget of the country. Besides, knowledge of the local solar
radiation is essential for the proper design of building energy systems, solar energy systems and
good evaluation of thermal energy environment within building.
1.3 Statement of the problem
The Ethiopian population will continue to grow for several decades to come. Energy
demand is likely to increase even faster, and the proportion of energy supplied by hydroelectricity
will also grow at the same rate. For the last several years Ethiopian Electric Power Corporation
(EEPCo) the only provider of power, has faced a critical power shortage. As part of the ongoing
fast economic development noted in the country, many factories had been established, adding that
this had increased local demands especially big cities like Diredawa for more electric power.
Coupled with climate change that has resulted in irregular rain for hydroelectric power had
worsened the situation.
[2, 3, 8]
The city of Diredawa depends solely on the hydroelectric power as source of energy for cooling,
heating, ventilation, light and many other applications. Therefore, an alternative renewable source
of energy should be assessed not only
as substitute to power supplied by the government but
also to reduce costs using solar thermal energy system.
4
Table 1.1: Ethiopia electric power tariff [2]
Range(kwh)
Price Rate(USD)
From
To
0
50
0.273
51
100
0.3564
101
200
0.4993
201
300
.55
301
400
.5666
401
500
0.588
501
1000000000
0.6943
1.4 Objective of the study
Located in the southeast of the Ethiopia, the city of Diredawa has a tropical desert
climate. In summer high temperature are typically 35 c and over 42 c on occasion. With
abundant sunshine Diredawa can offer one of the best renewable sources in the country and is
well situated to provide reliable substitute of hydroelectric power for residential building.
The burden on hydroelectric power could be alleviated by undertaking alternative energy
development and promotion program particularly on solar energy sources for residential
application.
5
The main objective of the study is to explore the prospects of solar thermal energy use as
substitute for residential building for the application of how water, heating, cooling and/or
ventilation considering this city as a model. The minor objective of this study is to inform policy
makers, promoters and general public about the country’s solar energy resource potential and to
strength public awareness about solar energy for economic development and environmental
issues and promote investment in this energy sector.
6
Chapter 2
BACKGROUND OF THE STUDY
2.1 Introduction
In Ethiopia, like in most developing African countries, the energy sector is dominated by
traditional energy, modern energy, electricity, petroleum and infrastructure for energy supply
exists mainly in urban areas. Adequate and reliable supply of energy is crucial for social and
economic development of any country. Easily access to affordable energy is often observed to be
associated with the stage of development. [3, 22]
Industrial countries that have already achieved high living standard have recorded higher
capita energy consumption while least developed countries like Ethiopia are listed as low per
capita energy consuming countries. Energy being the basic element of economic development
requires due consideration to serve the purpose. Efficient utilization of available energy and
improving the supply in quality are the key element in the development process. [3, 24]
Today, the relationship between energy and economic growth in Ethiopia has become the
main issue of the policy makers of the country. If economic activity is to be a measure of welfare
and continued growth, the implication of future energy development becomes central point of the
debate about energy policy. Slowing and eventually reversing growth in global greenhouse gas
emission will require, among other initiatives, the large scale of renewable energy technology for
producing thermal energy and hydroelectricity. The global environment facility is committed to
supporting the use of renewable energy technologies at an unprecedented scale through the world.
Over the next several decades, large scale application of solar electric technology could grow to
several hundred thousand megawatts. [2, 3, 22]
Information on the potential application of solar energy as a substitute can influence
investment decision, policy and national planning. Although long term average cost of solar
7
energy may be higher than for hydropower, diversification of energy supply will become more
important as climate change impacts cause drought and endanger the availability of hydro
resources. The reliability of solar energy resource overtime and phase relationship of this resource
relative to other fluctuating resource can therefore be important, without accessible high quality
information of solar energy development; opportunities for enhancing supply diversity and
security will be missed.
Availability of reliable and easily usable research and study is essential for government and
industry to identify in-country power generation potential from these options and to act on that
knowledge. This lack is a primary obstacle to both public-sector and private-sector investment in
renewable energy application in most of the developing country like Ethiopia.
2.2 Analysis of energy context
Ethiopia has one of the lowest rates of access to modern energy service; its energy supply is
primarily based on biomass. With a share of 94.4% of Ethiopia’s energy supply, waste and
biomass are the country’s primary energy sources, followed by 6.7% and hydropower 0.9%.
8
Figure 2.1: Share of Ethiopia’s energy supply 2008 (%) [24]
99% of households, 70% of industries and 94% of service enterprises use biomass as
energy source. Households account for 88% of total energy consumption, industry 4%, transport
3% and service and others 5%. The installed electricity generating capacity in Ethiopia is about
2060MW (88% hydro, 11% diesel and 1% thermal) and production covers only about 10% of
national energy demand. According to World Bank, only an estimated 12% of the Ethiopian
population has access to electricity. [24]
Almost all Electricity needs are provided by Ethiopian Electric Power Corporation
(EEPCo). The corporation has two electric energy supply systems: the inter-connected system
(ICS) and self-contained system (SCS). The main energy source of ICS is hydro power plant and
also the CSC are mini hydro’s and diesel power generators allocated in various areas of the
country. In the ICS, EEPCo currently operates 11 primarily large, one geothermal and 15 diesel
9
grid-connected power plants with a total of 1842.6MW, 7.3MW, and 172MW respectively.
Another three hydropower and several diesel off-grid power plants with a capacity of 6.15MW
and 31.34MW respectively operates as self-contained systems(SCS).As of July 2010, a total of
5163 towns and villages and a total of 1,896265 customers were connected to the ICS and SCS by
EEPCo. Approximately 87% of customers are domestic, 12% commercial and1.1% industrial
whereas 0.1% is used for street lighting. Average consumption per connected household is rather
low (747kwh/yr) or 47kwh/yr per capita, leaving a lot of potential for further growth. 500kwh/yr
is considered the average minimum level of consumption per-capita for reasonable quality of life
in the country. [2, 24]
The Electric power consumption (kWh per capita) in Ethiopia was 45.76 in 2009, according
to a World Bank report, published in 2010. Electric power consumption measures the production
of power plants and combined heat and power plants less transmission, distribution, and
transformation losses and own use by heat and power plants. The following figure shows a
historical data chart for Electric power consumption (kWh per capita) in Ethiopia.
10
Figure 2.2: Electric power consumption per capita in Ethiopia [4]
According to the Ethiopian Electric Power Corporation (EEPCo), Ethiopia’s total electricity
generation in 2010 was 3,981.07GWh. Although hydropower contributes only 0.9% to the total
energy supply, it generates 88% of electricity and is thus the country’s dominating electricity
resource, followed by Diesel (11%) and geothermal (1%) electricity generation.
11
Figure 2.3: Development of energy generation of EEPCo [24]
Figure 2.4: Electricity production from hydroelectric sources (% of total) [4]
12
There is no energy production from nuclear, natural gas and coal sources in Ethiopia. The
vast majority of Ethiopia's energy needs are met from natural sources. Nationally, biomass fuels
constitute approx. 93% of the final energy consumption, with 77% being derived from woody
biomass, 8.7% from crop residues and 7.7% from dung. Per capita energy consumption in
Ethiopia is among the lowest in the world (0.30 tone energy).
Table 2.1: World Bank Indicator- Ethiopia energy production and use [4]
No.
Energy production and use
2002
2009
1.0
0.9
1
Alternative and nuclear energy (% of total energy use)
2
Combustible renewable and waste (metric tons of oil
28469.4
equivalent)
Combustible renewable and waste (% of total energy)
92.7
Electric power consumption (kWh per capita)
41.3
Electric power consumption (kWh)
3212000000.0
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
29285.7
92.4
43.0
3419000000.0
Electric power transmission and distribution losses (kWh)
335000000.0
358000000.0
Electric power transmission and distribution losses
(% of output)
9.4
9.5
Electricity production from hydroelectric sources (kWh)
3385000000.0 3296000000.0
Electricity production from hydroelectric sources (% of
95.4
total)
Electricity production from oil sources (kWh)
162000000.0
Electricity production from oil sources (% of total)
4.6
Electricity production (kWh)
3547000000.0
Energy imports; net (% of energy use)
6.3
Energy production (kt of oil equivalent)
28760.5
Energy use (kg of oil equivalent per capita)
395.1
Energy use (kg of oil equivalent) per dollar1;000 GDP
526.2
Energy use (kt of oil equivalent) in Ethiopia
30703.5
Fossil fuel energy consumption (% of total)
6.3
87.3
467000000.0
12.4
3777000000.0
6.7
29581.2
399.1
490.4
31704.3
6.7
13
EEPCo has about 1.3 million customers including businesses, less than 10% households,
40% of them in capital city Addis Ababa, and about 5% in Diredawa. 95% of customers are
households and the rest is industrial and service sectors. However, the industrial and service
sectors, which accounts for only five percent of the number of customers consumes 69% of the
electric power.
At the moment, EEPCo’s maximum electric generating capacity is 814MW, 80% hydro and
20% geothermal and thermal. However because of various reasons including water shortage, most
of the time in summer the corporation generates only 600-700MW, unable to meet the growing
demand EEPCo is forced to start power sharing in most of the countries including the capital city
and Diredawa not only dividing daytime but also overnight especially for the residential building.
This difficult energy situation is no longer tenable at a time when the price of oil seems to
continue and the shortage of rainwater is happening time and again. The energy policy in Ethiopia
requires profound changes to gain healthy situation. This is both an economic and a social issue.
2.3 Current status of solar thermal market and challenges
Initiating a solar trade in Ethiopia is a complex and lengthy process in which all the
important element has to be exactly coordinated. Today solar energy foundation- Stifting
Solarergy i.e it has laid down the foundation in some areas for solar trade and training courses.
They decided to take a process with five steps and elements: 1.pilot project, 2. local product, 3.
training, 4. Micro-finance, and 5. Urban and rural service network has proved to be feasible. [7,
24]
14
Solar energy market assessments made in recent years (IGAD, EPV.Com, and SWERA)
unequivocally indicate that there exists enormous potential market for solar energy in Ethiopia.
According to the studies, there is compelling evidences that indicates that there is a significant
opportunity for solar energy in Ethiopia. Among these are:

A population of nearly 85 million, more than 80% of which is rural and un-electrified.

A considerable size of the rural population living in high-agricultural-potential and cashcrop-growing areas.

Extremely low electrification rates, with only 12% of the population having access to
electricity and almost non-existent access in all rural and some urban areas.

The scattered settlement pattern in rural Ethiopia makes rural electrification options other
than solar energy extremely unattractive.

The Government of Ethiopia is committed to the development of the rural agricultural
sector through the adoption of a twin-track rural electrification strategy (grid-based and
off-grid) to accelerate rural growth through expansion of electricity access by the rural
sector. The Government of Ethiopia has also established a rural electrification fund to
facilitate and support off-grid rural electrification projects.

Awareness about solar energy technology and its application has improved over the past
few years as a result of a few solar energy projects that were undertaken in some parts of
the country.
Some of the most important challenges and barriers that still need to be addressed include:

inadequate technical skills,

lack of innovative financing mechanism to draw-down upfront cost of systems,
15

inadequate awareness among policy makers as well as consumers,

lack of clear and coherent policy, and hence, institutional capacity to facilitate
commercialization of the technology, and

Poor linkages between the national level suppliers/dealers and local level retailers and
technicians.
What is still have to be done, above all, is an increased lobbying work and raising
awareness among Ethiopian government departments and local and foreign investors.
16
Chapter 3
REVIEW ON SOLAR THERMAL ENERGY SYSTEMS
3.1 Solar energy
Solar energy technologies can provide electrical generation by heat engine or photovoltaic
means, day lighting, solar hot water, and space heating in active solar active and passive solar
building, potable water via distillation and disinfection, space cooling by absorption or vaporcompression refrigeration, thermal solar cooking energy for cooking and high temperature
process heat for industrial purpose.
Solar energy technologies are broadly characterized as either passive or active depending on
the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic
panels, pumps, and fans to convert sunlight into useful output. Passive solar techniques include
selecting material with favorable thermal properties, designing spaces that naturally circulate air,
and referencing the position of building to the sun.
Active solar technologies increase the supply of energy and are considered supply side
technologies, while passive solar technologies reduce the need for alternate resource and are
generally considered as demand side technologies.
3.2 Solar thermal use
Solar thermal technologies can be used for water heating (including pool and spa), space
heating, and space cooling and process heat generation.
3.2.1 Solar water heating
Solar hot water system use sunlight to heat water. In low geographical latitudes (below 40
degrees) from 60 to 70% of domestic hot water use with temperature up to 60 degree Celsius can
be provided by solar heating systems. The most common types of solar water heaters evacuated
17
tube collectors (44%) and glazed flat plate collectors (34%) generally used for domestic hot
water, and unglazed plastic collectors (21%) used mainly to heat swimming pools.
3.2.2 Solar thermal for heating, cooling and ventilation
Thermal mass is any material that can be used to store heat; heat from sun in the case of
solar energy. Common thermal materials include stone, cement and water. Historically they have
been used in arid climate or warm temperature region to keep building cool by absorbing solar
energy during the day and radiating stored heat to the cooler atmosphere at night. However, they
can be used in cold temperature areas to maintain warm as well. The size and placement of
thermal mass depends on several factors such as climate, day light and shading conditions. When
properly incorporated, thermal mass maintains space temperature in a comfortable range and
reduce the need for auxiliary heating and cooling equipment.
Thermal mass can store solar energy in the form of heat at domestically useful temperature
for daily use or seasonal thermal duration. The well designed system can lower peak demand,
shift time-of-use to off-peak – peak hours and reduce overall heating and cooling requirements.
Unglazed transpired collectors (UTC) are perforated sun-facing walls used for preheating
ventilation air. UTCs can raise incoming air temperature up to 22 degree Celsius and deliver
outlet temperature of 45 to 60 degree Celsius. The short payback period (3-12 years) of transpired
collectors makes them more cost-effective alternative than glazed collection systems.
3.3 Solar thermal collectors and energy analysis
3.3.1 Solar collectors
Solar energy collectors are special kind of heat exchangers that transform solar radiation
energy to internal energy of the transport medium. The major component of any solar system is
the solar collector. This is a device which absorbs the incoming solar radiation, converts it into
heat, and transfers this heat to a fluid (usually air, water or oil) flowing through the collector. The
18
solar energy thus collected is carried from circulating fluid either directly to the hot water or
space conditioning equipment or to the thermal energy storage tank from which can be drawn for
use at night and/or cloudy days.
There are basically two types of solar collectors: non-concentrating or stationary and
concentrating or sun-tracking. A non-concentrating collector has the same area for intercepting
and for absorbing solar radiation, whereas a sun-tracking or concentrating collector usually has
concave reflecting surface to intercept and focus the sun’s beam radiation to a smaller receiving
area, thereby increasing the radiation flux.
In this study, for the convenience of assessment, only the review of stationary collectors in
particular FPC will be considered.
3.3.2 Stationary solar collectors
Solar energy collectors are basically distinguished by their motion. The stationary solar
collectors are permanently fixed in position and do not track the sun. Three types of collectors fall
in this category.
3.3.2.1 Flat plate collectors
When solar radiation passes through a transparent cover and impinges on the blackened
absorber surface of high absorptivity, a large portion of this energy is absorbed by the plate and
then transferred to the transport medium in the fluid tubes to be carried away for storage or use.
The underside of the absorber plate and the side of casing are well insulated to reduce conduction
losses. The liquid tubes can be welded to the absorbing plate. The liquid tubes can be welded to
the absorbing plate, or they can be an integral part of the plate. The liquid tubes are connected at
both ends by large diameter header tubes.
The transparent cover is used to reduce convection losses from the absorber plate through
the restraint of the stagnant air layer between the absorber plate and the glass. It also reduces
19
radiation losses from the collector as the sum transparent to the short wave radiation received by
the sun but it is nearly opaque to long-wave thermal radiation emitted by the absorber plate.
FPC’s are usually permanently fixed in position and require on tracking of the sun. The
collector should be oriented directly towards the equator, facing south in northern hemisphere and
north in the southern hemisphere. The optimum tilt angle of the collector is equal to the latitude
of the location with angle variation of 10-15˚ more or less depending on the application. [1]
Figure 3.1: Pictorial view of flat plate collector [1]
Flat plate collectors generally consists of the following components:

Glazing: one or more sheets of glass or other diathermanous (radiationtransmitting) material.

Tubes, fins or passages: to conduct or direct the heat transfer fluid from the inlet to
the outlet.
20

Absorber plate: flat, corrugated, or grooved plates, to which the tubes, fins, or
passages are attached.

Header or manifold: to admit and discharge the fluid.

Insulation: to minimize the heat loss from the back and sides of the collector

Container or casting: to surround the aforementioned components and keep them
free from dust, moisture, etc.
3.3.2.2 Compound parabolic collector
Compound parabolic collector (CPC) is non-imaging concentrators that have the capability
of reflecting to the absorber all of the incident radiation within wide limits. Their potential
as
collector of solar energy was pointed out by Winston. The necessary of moving the concentrator
to accommodate the changing solar orientation can be reduced by using a trough with two section
of a parabola facing each other.
Compound parabolic concentrators can accept incoming radiation over a relatively wide
range of angles. By using multiple internal reflections, any radiation that is entering the aperture,
within the collector acceptance angle, finds its way to the absorber surface located at the bottom
of the collector.
21
Figure 3.2: Schematic diagram of a compound parabolic collector [1]
3.3.2.3 Evacuated tube collectors
Conventional simple flat-plate solar collectors were developed for use in sunny and war
m climate. Their benefits however are greatly reduced when conditions become unfavorable
during cold, cloudy and windy days. Furthermore, weathering influences such as condensation
and moisture will cause early deterioration of internal materials resulting in reduced performance
and system failure. Evacuated heat pipe solar collectors (tubes) operate differently than the other
collectors available on the market.
ETC use liquid-vapor phase change materials to transfer heat at high efficiency. These
collectors feature a heat pipe (a highly efficient thermal conductor) placed inside a vacuum-sealed
tube. The pipe is then attached to a black copper fin that fills the tube (absorber plate). Protruding
from the top of the each tube is a metal tip attached to the sealed pipe (condenser). The heat pipe
contains a small amount of fluid that undergoes an evaporating-condensing cycle.
22
Figure 3.3: Schematic diagram of evacuated tube collector [1]
3.4 Thermal analysis of flat plate collectors
In this section the thermal analysis of the flat plate collector is presented. The basic
parameter to consider is the collector thermal efficiency. This is defined as the ratio of the useful
energy delivered to the energy incident on the collector aperture.
3.4.1 Flat plate collector performance
Under steady-state condition, the useful heat delivered by solar collector is equal to the
energy absorbed by the heat transfer fluid minus the direct or indirect heat losses from the surface
to the surrounding. A flat plate collector may have a performance value of 75% based on aperture
area, but because the gross area is almost the same as aperture, the gross value will only be a few
% lower. The performance of the glazed flat plate collector is better than the evacuated tube at
low temperature and better than the unglazed at high temperature.
23
Figure 3.4: Efficiency of stationary solar collectors. [9]
3.4.2 Thermal efficiency of flat plate collector
Thermal efficiency of FPC is a dimensionless performance measure of a device that uses
thermal energy. It is the ratio between the useful output of a device and input in energy terms.
Due t to friction, heat loss, and other factors, thermal efficiencies are typically much less than
100%. Thermal performance tests of FPC conducted Florida Solar Energy Center of USA is in a
very good agreement with thermal performance test reported by institute at Hchschul Rapperswil
of Switzerland as compared by the following graph.
24
Figure 3.5: Thermal efficiency of flat plate solar collector [20]
25
Chapter 4
DATA COLLECTION AND MODELING
4.1 Diredawa city specification
For the purpose of modeling, some of the specifications related to this study will be discussed
in the following sections. Some of them are: population size, climate, geographic locations and
residential building types.
4.1.1 Population size
The 2007 population and housing census of Ethiopia reported that Ethiopia had 85 million
populations while the city of Diredawa has 342,827. The census reported that there are 75,693
households with an average 4.0 person per household. [4].
In this study it is considered that a family composed of a couple and two children. An
occupancy schedule is defined by considering that one of the spouses work usually husband and
the two children are students.
4.1.2 Climate and geographic location
Diredawa is located between 90 28.1˚N and 90 49.1˚N Latitude and between 410 38.1˚E
and 420 19.1˚E longitude. The city administration consists of 9 urban and 38 rural kebeles. The
city has a total land size of 1288 square kilometers of which 97.73% accounts for the size of the
rural area while the remaining 2.27% covers the land size of the urban areas found in the city
administration.
The city has a warm and dry climate with a low level of precipitation. The annual
maximum and minimum air temperature are 37.4˚c and 18.2˚ respectively. Diredawa has an
average annual rainfall of 604 millimeters. The range of altitude in the city is between 960-2500
meters above sea level.
26
Figure 4.1: Global horizontal solar radiation of Ethiopia [24]
4.1.3 Residential building types
Defining the characteristics of the residential building in the Diredawa city is an essential
element in this study since the thermal system must be adapted to the housing. 84% of the
buildings in the city are residential. A majority of housing has an area between100-150 meter
square. Reinforced concrete associated with clay bricks or concrete blocks represent the main
component of the construction element of the building.
A typical representative home is an apartment in a current floor, since an important number
of residents are collective and situated in the city where the solar thermal energy can be first
27
developed. The apartment has 150 meter square and it comprises two bedrooms, a lounge, living
room, a kitchen and a bathroom. The floor height is taken as 3m.
4.2 Modeling and Simulation
4.2.1 Introduction
The proper sizing of the components of a solar system is a complex problem which includes
both predictable (collector and other components) and unpredictable (weather data) components.
Computer modeling of thermal systems presents many advantages the most important of
which are the following [1].

Eliminate the expense of building prototypes.

Complex systems are organized in an understandable format

Provide thorough understanding of the system operation and component interaction

It is possible to optimize the system components

Estimate the amount of energy delivery from the system

Provide temperature variations of the system

Estimate the design variable changes on system performance by using the same
weather condition.
Polysun simulation program (which is chosen for this study) provides dynamical annual
simulations of solar thermal systems and helps to optimize them. It operates with dynamic time
steps from 1s to 1h, thus simulation can be more stable and exact. The program is user friendly
and the graphic-user interface permits a comfortable and clear input of all system parameters. All
aspects of the simulation are based on physical models that work without empirical correlation
terms. In addition the program performs economic viability analysis and ecological balance,
28
which includes emissions from the eight most significant greenhouse gasses, thus the emissions
of the systems working only with conventional fuel and systems employing solar energy can be
compared. Polysun program was validated by Gantner and was found to accurate to within 510%.
To simulate solar thermal energy system by polysun program the following information
is needed.

Location selection either from database or map and its latitude, longitude and altitude
( for map continent, country and city)

Electric grid – grid voltage

Consumer( loads) desired e.g. domestic hot water(DHW), space heating, pool or
process heat

Selecting energy providers: solar thermal, heat pump, boiler or chiller

System specifications (system size, collector/generator field, preparation method and
template source)

Hot water demand ( number of persons, temperature, daily/annual demand)

Building specification (building dimensions, number of floor, air-conditioned living
area and heating set point temperature-day)

Dimension of the solar thermal system ( define the collector field and tank)

Heat generator ( define the heat generator; boiler or heat pump)
4.2.2 Simulation data
Solar thermal system is an assembly of collection of devises, storage devices, and load
devices that the system requires. The system is defined in the simulation file. The simulation data
controls the simulation.
The simulation data contains information about the physical
29
characteristics of collector device, the storage device, building type, the load, location and
template file.
The following data is defined for this study to run simulation program based on the weather
and need of the location selected.
1. Location selection from data base:

Region- Africa

Country- Ethiopia

Location( city)- Diredawa
2. Electric grid voltage: 230V
3. Consumers need/ load: Domestic hot water and Space heating/cooling
4. Energy Provider: Solar system and/or heat pump
5. System Specification:

System size: residential system

Collector/Generator field: single field

DHW preparation method: fresh water station

Template source: space heating/cooling and hot water ( heat pump and
solar thermal)
6. Number of persons living in the building: 4
7. Temperature: 122˚F
8. Daily hot water demand: 80gal
9. Building: single family house, low energy
10. Building dimension: 35.1ft x 23ft
11. Number of floors: 1
30
12. Heating set point temperature-day: 66.2˚F
13. Heated/ air-conditioned living area: 1612.4 square ft
14. Heating loop convector (inlet/return temperature): Floor heating
15. Solar Thermal:

Test Standard: Europe

Collector: Flat-plate

Orientation:0

Tilt angle: 10˚

Number of collector: 6

Gross area: 127.17 square ft

Tank volume: 158.5gal

Water tank: 600l for heat pump

Heat generator power: 47kBtu/hr
31
Chapter 5
ANALYSIS OF SIMULATION
5.1 Result
To develop our model we chose to work on polysun simulation software because of its
user friendly and the graphic-user interface permits a comfortable and clear input of all the
system parameters. It also provides dynamical simulations of solar thermal systems and helps to
optimize them.
Model System 1
Space heating/air conditioning and hot water (Solar thermal only)
Figure 5.1: System diagram (solar thermal only)
32
Location of the system
Ethiopia
Diredawa
Longitude: 41.83°
Latitude: 9.58°
Elevation: 5,574ft
For calculation polysun uses database of several thousands of hourly weather files
provided by software meteonorm. Regarding Ethiopia the database includes the climatic file of
selected cities like Diredawa. The data file for Diredawa city was generated from climate file of
meteonorm and the result of the simulation is tabulated in the following tables and graphs.
Table 5.1
System overview (annual values)
Total fuel and/or electrical energy consumption of the
system [Etot]
Total energy consumption [Quse]
System performance (Quse / Etot)
Comfort demand
26.1 Mcal
2,490 Mcal
95.5
Energy demand covered
Table 5.2
Meteorological data overview
Average outdoor temperature
68.6 °F
Global irradiation, annual sum
Diffuse irradiation, annual sum
181.5 Mcal/ft²
56.4 Mcal/ft²
33
Table 5.3
Overview solar thermal energy (annual values)
Collector area
Solar fraction total
129.2 ft²
100%
Solar fraction hot water [SFnHw]
Solar fraction building [SFnBd]
100 %
100 %
Total annual field yield
Collector field yield relating to gross area
6,332.2 Mcal
49 Mcal/ft²/Year
Collector field yield relating to aperture area
Max. energy savings
54.5 Mcal/ft²/Year
-
Max. reduction in CO2 emissions
-
Table 5.4
Overview heat pump (annual values)
Seasonal performance factor for air-to-water heat
pump
Total electrical energy consumption when heating
[Eaux]
Total energy savings
Total reduction in CO2 emissions
0
0 Mcal
0 Mcal
0 pound
34
Table 5.5
Component overview (annual values)
Collector
Flat-plate, good quality
Data Source
Number of collectors
SPF
6
Number of arrays
Total gross area
ft²
1
129.17
Total aperture area
Total absorber area
ft²
ft²
116.25
116.25
Tilt angle (hor.=0°, vert.=90°)
Orientation (E=+90°, S=0°, W=-90°)
°
°
10
0
Collector field yield [Qsol]
Irradiation onto collector area [Esol]
Mcal
Mcal
6,332.2
21,359.3
Collector efficiency [Qsol / Esol]
Direct irradiation after IAM
%
Mcal
29.6
14,113.8
Heat pump
Heating power at A2/W35
Heat pump 10 kW
kBtu/hr
34.47
Electrical power at A2/W35
COP at A2/W35
kBtu/hr
11.26
3.1
DeltaT at A7/W35
R
18
Building
Single family house, low-energy building
Heated/air-conditioned living area
Heating setpoint temperature
ft²
°F
1,612.4
66.2
Heating energy demand excluding DHW [Qdem]
Specific heating energy demand excluding DHW
[Qdem]
Solar gain through windows
Mcal
6.5
Mcal/ft²
0.004
Mcal
11,145.5
Total energy losses
Mcal
16,954.1
Heating element
Number of heating/cooling modules
Floor heating
-
3
kBtu/hr
3
Power per heating element under standard
conditions
Nominal inlet temperature
°F
104
Nominal return temperature
Net energy from/to heating/cooling modules
°F
Mcal
95
-0.04
Hot water demand
Constant
Volume withdrawal/daily consumption
Temperature setting
gal/d
°F
80.3
122
Energy demand [Qdem]
Mcal
2,818.5
External heat exchanger Potable water
Transfer capacity
medium
W/K
10,000
35
External heat exchanger Solar loop
Transfer capacity
medium
W/K
Pump Solar loop
Eco, small
Circuit pressure drop
Flow rate
psi
gpm
3.756
0.7
Fuel and electrical energy consumption [Epar]
Mcal
12
Pump Potable water
Circuit pressure drop
Eco, small
psi
0.043
Flow rate
Fuel and electrical energy consumption [Epar]
gpm
Mcal
1.9
1.3
Pump Transfer circuit
Eco, small
Circuit pressure drop
Flow rate
psi
gpm
0.019
0.7
Fuel and electrical energy consumption [Epar]
Mcal
12
Storage tank Buffer tank
Volume
600l model for heat pumps
158.5
gal
Height
Material
ft
10,000
5.58
Steel
Insulation
Thickness of insulation
in
Rigid PU foam
3.1
Heat loss
Connection losses
Mcal
Mcal
890.5
882.3
Table 5.6: Solar loop
Solar loop
Fluid mixture
Fluid concentration
%
Propylene mixture
33.3
Fluid domains volume
Pressure on top of the circuit
gal
psi
4.2
58.016
36
Figure 5.2: Solar thermal energy to the system [Mcal]
Figure 5.3: Total fuel and/or electrical energy consumption of the system [Mcal]
37
Table 5.7
Total system report of solar thermal
Year Jan
Feb
Mar
Apr
Solar thermal energy to the system [Qsol]
Aug
Sep
Oct
Nov
Dec
Mcal 6332
542
498
560
535
544
515
524
512
Total fuel and/or electrical energy consumption of the system [Etot]
502
540
523
537
Mcal 25
2
2
2
2
Irradiation onto collector area [Esol]
May
2
Jun
Jul
2
2
2
2
2
2
2
1703
1722
1758
1614
1747
1788
1777
2
2
2
2
2
2
2
Mcal 3574
306
278
311
302
309
291
295
Heat loss to indoor room (including heat generator losses) [Qint]
293
287
302
295
306
Mcal
208
211
197
208
212
214
23
23
20
22
23
23
Mcal 21359 1792 1818 2018 1814 1808
Electrical energy consumption of pumps [Epar]
Mcal 25
2
2
2
Total energy consumption [Quse]
2522
209
202
227
2
213
2
217
204
Heat loss to surroundings (without collector losses) [Qext]
Mcal
269
22
21
24
23
23
23
The solar azimuth angle is the azimuth angle of the sun. It is most often defined as the angle
from due north in clockwise direction. Sun height, height angle, solar altitude angle or elevation
is the angle between the horizon and a line from the site toward the center of the sun. From our
simulation, the solar azimuth angle of Diredawa is calculated to be 50˚ as shown by the following
graph.
38
Figure 5.4: Horizontal line of the sun
During the day the sun has different position. In summer collector daily maximum
temperature is 300˚F while in winter the collector daily minimum temperature is 100˚F.
Simulation of collector daily maximum temperature is shown by the following graph.
Figure 5.5: Collector daily maximum temperature [˚F]
39
The analysis of the solar system is conducted in two models. Financial analysis of model
system one is tabulated as the following. The economical savings resulting from model one (solar
thermal only) application is calculated to be zero. This makes model one economically infeasible.
But, the system fully covered the energy demand of the application.
Table 5.8
Financial analysis of solar thermal system
Purchase costs
10,000 USD
Life span
30 years
Proportional incentives
25 %
Incentives per area
0 USD
Fixed incentives
0 USD
Heat generation tariff
0.4 USD
Inflation
2%
Interest
3%
Increase of energy prices
5%
Natural gas H
3.136 USD/therms; 0.171 USD/Mcal
Effective purchase cost after grants
7,500 USD
Annual energy cost savings
0 USD
Solar energy cost per kWh
0 USD
Annual income from heat generation tariff
2,627.908 USD
Payback period
4 years
Present value of the system
91,132.617 USD
Net present value
83,632.617 USD
40
Model System 2
Space heating/ air conditioning and hot water (Heat pump and Solar Thermal)
Figure 5.6: System diagram (heat pump and solar thermal)
Table 5.9
System overview (annual values)
Total fuel and/or electrical energy consumption of the
system [Etot]
Total energy consumption [Quse]
System performance (Quse / Etot)
Comfort demand
42.3 Mcal
3,576 Mcal
84.52
Energy demand covered
41
Table 5.10
Overview solar thermal energy (annual values)
Collector area
Solar fraction total
86.1 ft²
99.4%
Solar fraction hot water [SFnHw]
Solar fraction building [SFnBd]
99.4 %
99.4 %
Total annual field yield
Collector field yield relating to gross area
5,873.5 Mcal
68.2 Mcal/ft²/Year
Collector field yield relating to aperture area
Max. energy savings
75.8 Mcal/ft²/Year
3,857.2 Mcal
Max. reduction in CO2 emissions
5,304.8 pound
Table 5.11
Overview heat pump (annual values)
Seasonal performance factor for air-to-water heat
pump
Total electrical energy consumption when heating
[Eaux]
Total energy savings
Total reduction in CO2 emissions
3.3
11.2 Mcal
25.4 Mcal
34.9 pound
42
Table 5.12
Component overview (annual values)
Collector
Flat-plate, good quality
Data Source
Number of collectors
SPF
4
Number of arrays
Total gross area
ft²
1
86.11
Total aperture area
Total absorber area
ft²
ft²
77.5
77.5
Tilt angle (hor.=0°, vert.=90°)
Orientation (E=+90°, S=0°, W=-90°)
°
°
10
0
Collector field yield [Qsol]
Irradiation onto collector area [Esol]
Mcal
Mcal
5,873.5
14,239.5
Collector efficiency [Qsol / Esol]
Direct irradiation after IAM
%
Mcal
41.2
9,409.2
Heat pump
Heating power at A2/W35
Heat pump 10 kW
kBtu/hr
34.47
Electrical power at A2/W35
COP at A2/W35
kBtu/hr
11.26
3.1
DeltaT at A7/W35
Performance factor
R
18
3.27
Energy from/to the system [Qaux]
Fuel and electrical energy consumption [Eaux]
Mcal
Mcal
36.5
11.2
Energy savings solar thermal
CO2 savings solar thermal
Mcal
pound
3,857.2
5,304.8
Energy savings heat pump
CO2 savings heat pump
Mcal
pound
25.4
34.9
Building
Heated/air-conditioned living area
Single family house, low-energy building
ft²
806.2
Heating setpoint temperature
Heating energy demand excluding DHW [Qdem]
°F
Mcal
66.2
4.3
Specific heating energy demand excluding DHW
[Qdem]
Solar gain through windows
Total energy losses
Mcal/ft²
0.01
Mcal
Mcal
5,574.2
8,478.2
Heating element
Floor heating
Number of heating/cooling modules
Power per heating element under standard
conditions
-
2
kBtu/hr
3
Nominal inlet temperature
Nominal return temperature
°F
°F
104
95
Net energy from/to heating/cooling modules
Mcal
-0.03
43
Hot water demand
Volume withdrawal/daily consumption
Constant
gal/d
80.3
Temperature setting
Energy demand [Qdem]
°F
Mcal
122
2,818.5
External heat exchanger Potable water
medium
Transfer capacity
W/K
10,000
External heat exchanger Solar loop
Transfer capacity
medium
W/K
10,000
Pump Solar loop
Eco, small
Circuit pressure drop
Flow rate
psi
gpm
1.552
0.5
Fuel and electrical energy consumption [Epar]
Mcal
14.9
Pump Potable water
Circuit pressure drop
Eco, small
psi
0.044
Flow rate
Fuel and electrical energy consumption [Epar]
gpm
Mcal
1.9
1.3
Pump Transfer circuit
Eco, small
Circuit pressure drop
Flow rate
psi
gpm
0.01
0.5
Fuel and electrical energy consumption [Epar]
Mcal
14.9
Storage tank Buffer tank
Volume
600l model for heat pumps
gal
158.5
Height
Material
ft
5.58
Steel
Insulation
Thickness of insulation
in
Rigid PU foam
3.1
Heat loss
Connection losses
Mcal
Mcal
731.2
669.6
44
Table 5.13: Solar loop
Solar loop
Fluid mixture
Fluid concentration
%
Propylene mixture
33.3
Fluid domains volume
Pressure on top of the circuit
gal
psi
3.4
58.016
Figure 5.7: Solar thermal energy to the system [Mcal]
45
Figure 5.8: Fraction of solar energy to the system (%)
Figure 5.9: Heat generator energy to the system [Mcal]
46
Figure 5.10: Total fuel and/or electrical energy consumption of the system [Mcal]
Table 5.14
Total system report- solar thermal and heat pump
Year
Jan
Feb
Mar
Apr
Solar thermal energy to the system [Qsol]
Mcal 5874 499
483
529
503
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
501
469
474
473
458
499
488
497
Heat generator energy to the system (solar thermal energy not included) [Qaux]
Mcal 37
11
0
0
0
0
11
0
0
7
8
0
0
Heat generator fuel and electrical energy consumption [Eaux]
Mcal 11
3
0
0
0
0
3
0
Solar fraction: fraction of solar energy to system [SFn]
%
99.4 97.9
100
100
100
100
97.7
100
0
2
2
0
0
100
98.6
98.4
100
100
5
5
3
3
Total fuel and/or electrical energy consumption of the system [Etot]
Mcal 42
6
2
3
3
3
6
3
3
Irradiation onto collector area [Esol]
Mcal 14240 1195 1212 1346 1209
1206
1135
1148
1172
1076
1165
1192
1184
3
3
3
3
3
3
3
291
295
293
286
302
296
306
Heat loss to indoor room (including heat generator losses) [Qint]
Mcal 2123 178
181
201
178
182
168
165
174
166
177
179
174
Heat loss to surroundings (without collector losses) [Qext]
Mcal 248
20
22
24
21
21
19
20
18
20
22
21
Electrical energy consumption of pumps [Epar]
Mcal 31
3
2
3
3
3
Total energy consumption [Quse]
Mcal 3576 306
278
311
303
309
19
47
In the second model system simulation, the number of collector is reduced from 6 to 4. In
addition to covering energy demand of the application, this model resulted in annual energy cost
savings of 897.179 USD. The payback period of system application is 3 years whereas 4 years for
the first model. This makes the second model feasible when compared to the first one.
Table 5.15: Financial analysis- solar thermal and heat pump
Purchase costs
10,000 USD
Life span
30 years
Proportional incentives
25 %
Incentives per area
0 USD
Fixed incentives
0 USD
Heat generation tariff
0.4 USD
Inflation
2%
Interest
3%
Increase of energy prices
5%
Electricity
0.2 USD/kWh(el.); 0.2 USD/kWh
Effective purchase cost after grants
7,500 USD
Annual energy cost savings
897.179 USD
Solar energy cost per kWh
0 USD
Annual income from heat generation tariff
2,732.363 USD
Payback period
3 years
Present value of the system
119,092.695 USD
Net present value
111,592.695 USD
48
Figure 5.11: Collector daily maximum temperature of model two [˚F]
5.2 Discussion
The numerical simulation has enabled us to conduct a comparison between a housing
equipped with solar thermal system and the existing electricity supply. As the result from the
system model has revealed: if system model one is implemented only energy demand of the
system with no savings of energy cost at all. If the energy cost savings is of big interest
installation of solar thermal system couple with heat pump. The savings obtained if system model
two implemented is about $897.179 a year per households.
Average electric energy consumption per household is 747kwh/yr. It is very low compared
to even developing country. It cost about $300 for a year consumption of electric energy.
Therefore it is a good investment to substitute for solar thermal energy system not only for energy
savings of the house but also for the reduction of carbon dioxide emission to environment
eventhough Ethiopia is not one of the countries that release high amount it.
49
The review of electricity pricing seems inevitable. Indeed, the low price of electricity sold to
individuals artificially lowers the interest of other energy sources, including solar thermal.Thus,
the country is deprived of the natural assets it has. An increase in electricity prices might be a
solution and can rapidly increase the value of solar thermal energy market in Ethiopia. In addition
to these actions, measures must be taken to encourage the citizen to turn to solar thermal.
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Chapter 6
CONCLUSION AND FUTURE WORK
6.1 Conclusion
The analysis of the Ethiopian energy sector highlighted the need to find the solution for
alternative energy source and reducing the heavy energy cost. Because of high potential for
energy savings that the residential sector represents, the impact of solar thermal equipment
application in a typical residential building is evaluated. An assessment of solar thermal energy
resource has been developed for Ethiopia considering Diredawa as model because of its weather
condition. The study shows that there exists high potential resource through the year for virtually
all locations in Ethiopia for Solar thermal energy applications, heating or air conditioning and
solar hot water. In general, this study shows us that in the present circumstances, the market for
solar thermal in Ethiopia cannot be achieved as needed. Indeed, payback period on investment
obtained from our simulation is enough to significantly increase the solar thermal market. A
mobilization must take place either at the government level than at the level of stakeholders:
manufacturers, vendors, but also professionals. In addition, two essential parameters have to be
considered: the cost of electricity and equipment price. Competition is expected to lead to lower
the price of equipment. Even if it is already underway, the price will reach a certain threshold
below which they do not go. If the financial situation of Ethiopian state does not allow it to
directly subsidize solar installations, it may use the fiscal leverage to encourage the marker
development: reduction in VAT on equipment, reductions in tariffs and taxes, individual credits.
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6.2 Future work and recommendation
This work is limited in its scope on the study of solar thermal energy use as substitute
only. The importance of this study is to provide information on solar thermal energy potential of
Ethiopia. From this point of view, this study could be considered as a reference for any solar
energy utilization technology. To know the exact solar resource potential of Ethiopia and to solve
the problem of rural electrification of the country, more studies should be conducted further in the
area of PV in the future.
Assessment of Ethiopia’s solar thermal resource base indicates that the country has huge
potential for solar energy application as substitute. There are, however, challenges like low
purchasing power, unfavorable public attitude towards the private sector and unfair regulations
that work against development and application of solar thermal energy technologies. It is thus
recommended that the government, nongovernmental organization and public make coordinated
effort to overcome the challenges by using flexible approaches to improve the current state of
energy crisis.
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