Page | 1

Case Study SA-CT3MINI HYDRO-POWER GENERATION IN WATER DISTRIBUTION SYSTEMS

Ref Case Study SA-CT3 Response information, description and remarks1 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 cross-flow 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.

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.

Page | 2

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 hydro-power 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.

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.

Page | 3

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.

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

17 Confidence grade: High; research project by University of Pretoria for the Water Research Commission.

18 Reference / Information source University of Pretoria. Department of Civil Engineering

Page | 4

Case Study SA-CT3MINI 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 | 5

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.

Electricity utilizationThe 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 actionsThe 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 | 6

Financing arrangements in South AfricaThe 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 requirementsNo 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