Design and implementation of conduit hydropower plants in the City of Tshwane

Marco van Dijk Chantel Niebuhr Anja Bekker

As a water-scarce country, it is often presumed that South Africa does not have the most prevalent hydropower conditions, as may be found elsewhere in Africa and the rest of the world. However, large quantities of raw and potable water are conveyed daily over large distances and elevations under either pressurised or gravity conditions. Within these systems exists the opportunity for conduit hydropower generation.

In water distribution systems, excess pressure, which can be exploited for conduit hydropower, is generally dissipated by employing equipment such as orifice plates and pressure-reducing valves. Conduit hydropower differs from more conventional hydropower development in that it is not located on natural rivers or waterways, and does not involve the potential negative types of environmental impacts that are usually associated with hydropower projects. The water supply and distribution systems consist of a complex network of interconnected pipes, service reservoirs and pumps that deliver water from the treatment plant to the consumer.

The Hydropower Research Group has been actively involved in the following activities:

South African policy and legislation Feasibility studies Site evaluations Small-scale hydropower plant development Turbine development and design Numerical computational fluid dynamics modelling Guideline and software tool development

A Memorandum of Agreement, cementing the collaboration between research group’s opportunities to evaluate, plan, design, experiment and develop conduit hydropower plants on the water infrastructure of the City of Tshwane.

In 2011, the Pierre van Ryneveld conduit hydropower plant was launched, showcasing a 15 kW cross-flow turbine installed on the reservoir roof.

The research group also assisted in the development of the Annlin Reservoir conduit hydropower plant, which consisted of three 50 kW pump-as-turbine installations, with two grid-connected units and one unit supplying the reservoir complex. Unfortunately, this site was vandalised (a reality for most municipalities) and requires refurbishment. Three pump-as-turbine installations at the Annlin Reservoir

The Otter turbine installed on a bypass in the University of Pretoria and the City of Tshwane, endorsed the

parallel to pressure-reducing valves

A new reservoir was recently completed in Doornkloof. An 8 kW prototype “Otter turbine” was installed as part of this construction. This conduit hydropower plant was recently commissioned and supplies the site with power for lighting, telemetry, cathodic protection and an alarm system. A student completing his master’s degree in the Department of Civil Engineering is now optimising the design and monitoring the functioning.

A collaboration objective between the City of Tshwane and the City of Aarhus in Denmark incorporates evaluating the Salvokop Reservoir site for its conduit hydropowergeneration potential. The Salvokop Reservoir complex is located south of the Pretoria Central Business District, and a new 30 Mℓ reservoir is being planned adjacent to the existing 27 Mℓ reservoir.

The Embassy of Denmark facilitated the cooperation, and the Hydropower Research Group conducted the feasibility study and eventually the design of this 152 kW conduit hydropower plant to be installed in the existing pressure-reducing valve chamber. Approximately 245 ℓ/s flows from the Fort Klapperkop reservoirs under gravity to the Salvokop Reservoir, where an excess pressure of ±78 m requires dissipation. The City of Tshwane has approved the allocation of funds in the 2021/22 budget for this installation to be implemented. The Hydropower Research Group conducted a feasibility study for the City of Tshwane, which found that more than 2.4 MW of hydropower potential exists in five of the larger reservoir complexes in the City of Tshwane. Two of these sites are the two Heights reservoirs located close to the Voortrekker Monument. Initially, two conduit hydropower plants were planned at the Heights High Level and Heights Low Level reservoirs, respectively, but these two sites were sensibly combined into one installation. Currently, a hybrid pressure-control station and conduit hydropower plant is being constructed, which will ultimately house two Francis-type turbines of 265 kW and 455 kW, which will be connected to the City of Tshwane’s electrical grid.

The design layout of the 152 kW conduit hydropower plant at

Salvokop Reservoir The Heights hybrid pressure-reducing station and conduit hydropower plant

The need for power in remote locations remains a reality for a large metropolitan municipality like the City of Tshwane. As part of a master’s degree study, an inline pressure wheel was developed to allow for power generation anywhere along a pipeline. At the Klipgat Reservoir in Mabopane, a 300 W inline pressure wheel was installed that will supply power to the site. This is a very simple design with an inline wheel installed on top of the pipe, enclosed and connected to an axle and a pulley system with an alternator.

Following the promising pilot projects undertaken around South Africa, and a presentation by the Hydropower Research Group to the City of Tshwane in 2013, a Mayoral Resolution was taken that all new reservoirs in the city would consider the inclusion of hydropower. With this decision, the City of Tshwane aims to meet a goal that was set for the sustainable management of water, energy, waste and ecological environmental management.

The City of Tshwane’s hydropower plants illustrate how existing municipal infrastructure can be utilised to meet South Africa’s sustainable energy goals, while providing essential services to consumers. The City of Tshwane should be used as an example to other municipalities to realise the potential that is available within their existing water infrastructure. Additionally, projects such as these showcase the possibility for innovation within the hydropower sector. Conduit hydropower development through pilot studies and installations allow for a broader range of applications of retrofitted traditional hydropower systems, as well as new innovative designs. As South Africa struggles through the current electricity supply crisis, reliable, localised and sustainable energy production is an invaluable alternative and asset for the water industry.

A pico inline pressure wheel hydropower turbine installation at Klipgat Reservoir