Lesotho Highlands Water Project’ s happy spin-off
It is highly gratifying when sound and well-planned mega infrastructure projects have positive and often unplanned spin-offs. By Helgard Muller, Pr Eng
When the Lesotho Highlands Water Project( LHWP) was planned, it did include a hydropower component at Muela in Lesotho, but at the time, nobody thought that additional electricity could be generated with the‘ new water flows’ from the South African rivers flowing towards the Vaal Dam. The Stortemelk small hydropower plant is such a positive spin-off of the LHWP— relatively small, but with significant implications. The global driving forces behind renewable energy alternatives are environmental as well as energy security concerns. Wind, solar, and hydro all have untapped potential of renewable energy. Renewable energy has made significant strides in South Africa over the past couple of years, with hydropower being the most established and universalised renewable energy technology across the globe. Water from the LHWP is transferred through a gravity tunnel from the Katse Dam in Lesotho into the Ash River near the town of Clarens and eventually lands up in the Vaal Dam. The Ash River was, by origin, a small river until the LHWP discharges augmented the natural flow by almost 500 times to an annual average flow of 24.5m 3 / s. Flows will further increase to approximately 40m 3 / s once Phase II of the LHWP comes fully on stream. To mitigate significant erosion caused by the greatly increased and varying flow, several structures were erected along the river, including the Botterkloof Dam.
The dam comprises a composite structure with a rolled concrete construction( RCC) central spillway and earth embankments on the two flanks. It is approximately 17.5m high and is owned by the Department of Water and Sanitation( DWS). While watching the energy being dissipated in the dam’ s spillway— therefore effectively being wasted— a private developer envisaged the idea to harness the same water for power generation. The river also offered rapids some 1.6km downstream, which also showed potential for hydropower generation.
Aurecon conducted the feasibility study in 2010 for both sites on behalf of REH Project Development. The study included the combined options, which concluded that the most optimum solution would be to implement two cascading schemes separately owing to better advantages, such as reduced capital investment, reduced risks, better return on investment, reduced impact on the canoeists who use the river for recreational purposes, and reduced land acquisition.
The upper of the two schemes, the Stortemelk Hydropower Station, is located on the left bank in-between the existing concrete spillway of the Botterkloof Dam and the spillway of the Boston A Dam, as shown in Figure 1.
Stortemelk Hydro( Pty) Ltd, a Special Purpose Vehicle company created solely for the implementation of the project, then submitted a bid( reverse auction) to the Department of Energy under Round Two of the Renewable Energy Independent Power Producer Programme( REIPPP). After being named a preferred bidder, a Power Purchase Agreement( PPA) was signed with Eskom Holdings. The project is financed under a Project Finance with Limited
Helgard Muller
Water, Sewage and Effluent( WSE) welcomes Helgard Muller as a regular contributor to this publication. Helgard recently retired from the Department of Water Affairs, where he served as deputy director-general: Policy and Regulations. His vast knowledge in policy and regulations at the Department of Water and Sanitation will add huge value to WSE.
Recourse structure, with 70 % of the debt funded by the Rand Merchant Bank of South Africa and the remaining 30 % funded via equity( Rochecouste Collet, Blersch & Olivier, 2016).
While engaging with the Aurecon team on this project, it became clear that modern hydropower is much more than just‘ water released from a reservoir that flows through a turbine and spinning it, which in turn activates a generator to produce electricity’. Scanning through a WRC study( Van Vuuren, 2010), I quickly learnt that there are a few bits more than a dam and a turbine, such as the specific design criteria for water flows into the penstock, different types of turbines, a facility to dissipate the unused or excess energy that is generated, as well as several protection systems.
Aurecon has provided engineering, procurement, and construction management( EPCM) services for the entire project. Construction of the 4.4MW hydropower station commenced in September 2014, and was commissioned ahead of time and under budget. Bertrand Rochecouste Collet, Stortemelk project leader at Aurecon, said,“ It means that the amount provided for contingencies was not even touched and all went as planned.”
According to international definitions, Stortemelk falls into the small hydropower category, because its generation capacity slots in-between 2.3 and 23MW, whereas mini hydropower generated is a facility of less than 2MW, micro hydropower is a facility of less than 300kW, and pico hydropower generated is a really tiny facility of less than 10kW( Van Vuuren, 2010).
The Stortemelk power station was designed to be fully automated, hence unstaffed, with only a caretaker visiting the site daily for routine checks and cleaning purposes. It offers remote access via secure web for all operations and control, as and when required. The design took into consideration comments from operation and maintenance company REH Operation & Maintenance, such as their experience with cooling water filtration systems, and the fact that maintenance can be simplified if all consumables are readily available on the local market and by using universal components.
The site posed a couple of specific geological challenges, such as the low bearing capability of the foundation and deep
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