Case Study SA-CT3
MINI HYDRO-POWER GENERATION IN WATER DISTRIBUTION SYSTEMS
Ref
Case Study SA-CT3
Response information, description and remarks
1
Location:
The Pierre van Ryneveld Reservoir is located south of Pretoria.
2
Sector:
Clean water (drinking water distribution systems).
3
Works Owner or Operator:
City of Tshwane
4
Size:
The City of Tshwane (now including Metsweding) receives Bulk water
from Rand Water, Magalies Water and own sources including Boreholes,
Water Purifications Plants and Fountains. Water is then distributed
through a large water system that includes 160 reservoirs, 42 water
towers, 10 677 km of pipes and more than 260 pressure reducing
installations (PRV’s) that operates at pressures up to 250 m.
5
Energy Provider:
Power generation project.
6
Process:
Water in water distribution networks is often fed under gravity from a
higher reservoir to another reservoir at a lower level. The high pressure
head at the receiving reservoir is then dissipated through the control
valves (altitude valves) or in some cases, orifice plates. In this
hydropower generating application, electricity is generated in a crossflow turbine using the available pressure head.
7
Component:
A cross-flow turbine is a water turbine where the water passes through
the turbine transversely, or across the turbine blades, unlike most water
turbines which have axial or radial flows.
Cross-flow turbine
As with a water wheel, the water is admitted at the turbine's edge. After
passing the runner, it leaves on the opposite side. Going through the
runner twice provides additional efficiency. When the water leaves the
runner, it also helps clean the runner of small debris and pollution. The
cross-flow turbine is a low-speed machine that is well suited for locations
with a low head but high flow. The subdivided regulating unit, the guide
vane system in the turbine's upstream section, provides flexible
operation. Low operating costs are obtained with the turbine's relatively
simple construction.
Page | 1
8
Motivation for the case study:
The University of Pretoria (UP) supported by the Water Research
Commission (WRC) is engaged in this research project to investigate the
potential of extracting the available energy from existing and newly
installed water supply and distribution systems. The project aims are to
enable the owners and administrators of the bulk water supply and
distribution systems to install small scale hydropower systems to
generate hydroelectricity for on-site use and in some cases to supply
energy to isolated electricity demand clusters or even to the national
electricity grid, depending on the location, type and size of installation.
9
Process/Plant Changes:
Feasibility studies aim to objectively and rationally uncover the strengths
and weaknesses of the venture, opportunities and threats as presented
by the environment, the resources required to carry through, and
ultimately the prospects for success. In its simplest term, the two criteria
to judge feasibility are cost required and value to be attained. In conduit
hydropower projects some may have a monetary value providing a fast
payback period whilst others have additional value, servicing remote
sites with subsequent benefits.
10
Civil/Physical Changes:
Minimal civil works need to be done for these mine hydro-power
installations, as the control valves are normally inside a control
room/valve chamber. No negative environmental or social effects
requires mitigation and the anticipated lead times should be short.
11
Operational Changes:
The operational requirements for monitoring and control of the hydropower plants are currently being assessed by the University of Pretoria
project team.
12
Risks and Dependencies:
What is the risk of cavitation at the plant?
Anytime a device or piece of equipment is placed within a pipeline, the risk
of cavitation exists. The cross-flow turbine is designed to limit the
possibility of cavitation over a wide range of conditions typically found
within pipelines.
What would happen if the generator or turbine fails?
Although highly unlikely, in this event the “pinch-valve” upstream of the
turbine will open and water would be discharged directly into the reservoir.
This will allow the control valves to close slowly and water will be
redirected through the parallel pressure control valve dissipating system.
13
Implementation:

Preliminary tests
The outcome of the three extensive field experiments provide enough
evidence, that there is sufficient flow and pressure at the inflow to the
Pierre van Ryneveld reservoir, to generate electric power on a pico
scale. The results of testing also indicated that pressure surges do occur
in the system and this will be used as a benchmark to ensure that the
hydropower plant does not result in an increase in risk for the pipe
system.

Turbine and generator selection and pilot plant design
The pilot plant utilizes a cross-flow turbine and a synchronous generator.
A steel frame with Cromadeck cladding was used to provide an
enclosure for the turbine, generator, electrical and monitoring equipment.

Commissioning
The Pierre van Ryneveld Conduit Hydropower Plant was launched in
November 2011 jointly by the City of Tshwane, the Water Research
Commission and the University of Pretoria when all the site lighting from
the conventional municipal grid over onto the hydropower generated on
site.
Page | 2
14
Energy Efficiency gains:
How much electrical energy can be produced from this pilot plant?
The maximum capacity is 15 kW of renewable, zero-emissions,
electricity but depends on the flow and head pressure conditions at any
given time. Annually ±131000 kWh could be generated with this unit,
enough to supply 10 households.
15
Cost/Benefit analysis:
The feasibility studies conducted thus far indicated that these types of
hydro power installations have a relatively short payback period. The
reason for this is the minimum amount of civil works required compared
to conventional hydro power projects. Due to very low profile of small
scale hydropower development in SA during two last decades there are
no defined approaches and methods for financing of hydroelectric
installations. Currently the Municipality’s or Water Board’s would utilize
their own budgets to finance such projects.
16
Project review:
The use of the potential energy stored in the pressurised closed conduit
water systems in Tshwane is not limited to the 10 larger sites identified in
the initial desktop study to generate up to 10 MWh of power. The scope
of using all available pressurised water system in Tshwane to convert
water pressure to electricity is still to be investigated and exploited
further.
17
Confidence grade:
18
Reference / Information source
For the generation of energy from the pressurized pipelines from Rand
Water, a factor of 10% was used. Capital and other costs were not reviewed
in this study. It will be required to conduct a thorough cost benefit
High; research project by University of Pretoria for the Water Research
analyses to prioritise the potential hydropower generation facilities.
Commission.
University of Pretoria. Department of Civil Engineering
Page | 3
Case Study SA-CT3
MINI HYDRO-POWER GENERATION IN WATER DISTRIBUTION SYSTEMS
Mini-hydropower (“conduit hydropower”) utilizes excess energy available in pressurised conduits
(pumping or gravity) to generate clean, renewable hydroelectric energy by means of a turbine.
Description of Process:
The water entering the reservoir still has excess energy which is normally dissipated by means of
pressure control valves. A parallel dissipating system, a water turbine, is installed and the water is
conveyed through the turbine where the flow and head is utilized to generate hydroelectric power.
Firstly, hydropower is a form of clean renewable and sustainable energy as it makes use of the
energy in water due to flow and available head without actually consuming the water itself. It does
not emit any atmospheric pollutants such as carbon dioxide, sulphurous oxides, nitrous oxides or
particulates such as ash. Secondly, hydropower schemes often have very long lifetimes and high
efficiency levels. Operation costs per annum can be as low as 1% of the initial investment costs. A
third advantage is that hydropower schemes often have more than one purpose. Hydropower
through water storage can help with flood control and supply water for irrigation or consumption,
and dams constructed for hydropower can also be used for recreational purposes. Different forms
of hydropower including reservoir, pumped storage and run-of-river systems of different sizes are
available and can be used for different forms of electricity generation.
How much electrical energy can be produced from this pilot plant?
The pilot plant utilizes a cross-flow turbine and a synchronous generator. The maximum capacity is
15 kW of renewable, zero-emissions, electricity but depends on the flow and head pressure
conditions at any given time. Annually ±131000 kWh could be generated with this unit, enough to
supply 10 households.
What is a cross-flow turbine?
A cross-flow turbine (Banki-Michell turbine or Ossberger turbine) is a water turbine where the water
passes through the turbine transversely, or across the turbine blades, unlike most water turbines
which have axial or radial flows.
Page | 4
As with a water wheel, the water is admitted at the turbine's edge. After passing the runner, it
leaves on the opposite side. Going through the runner twice provides additional efficiency. When
the water leaves the runner, it also helps clean the runner of small debris and pollution. The crossflow turbine is a low-speed machine that is well suited for locations with a low head but high flow.
The subdivided regulating unit, the guide vane system in the turbine's upstream section, provides
flexible operation. Low operating costs are obtained with the turbine's relatively simple
construction.
Electricity utilization
The electricity generated by this plant is used on site for the lighting, telemetry system, alarm
system and electric fence. Larger systems (higher kW output) could be connected to the electrical
grid thus reducing the demand from Eskom.
Failure response actions
The plant is designed to accommodate the full electrical load via a “heat sink” in case there is an
electrical demand failure. The heat sink is water cooled utilizing water from upstream of the turbine
discharging into the reservoir.
Completed installation of turbine, generator and electrical controls
Page | 5
Financing arrangements in South Africa
The feasibility studies conducted thus far indicated that these types of hydro power installations have a
relatively short payback period. The reason for this is the minimum amount of civil works required
compared to conventional hydro power projects. Due to very low profile of small scale hydropower
development in SA during two last decades there are no defined approaches and methods for financing
of hydroelectric installations. Currently the Municipalities or Water Boards would utilize their own
budgets to finance such projects.
Regulatory requirements
No water use permit is required as described in the Environment Conservation Act (Act 73 of 1989) and
the National Water Act (Act 36 of 1998) for most conduit hydropower projects. Any development will
have to comply with the requirements of the national environmental legislation (Act 73/1989 and Act
108/1998) and also with the provincial and the local government environmental legislation. Usually no
EIA is required.
Case Study SA-CT3
Page | 6