In 2015, the Drakenstein Municipality appointed Zutari for the Leliefontein Pump Station Project. The goal of the project was to increase the supply of potable water to Wellington to 30 Mℓ/d in the interim, and to 60 Mℓ/d in the future.
The location for the Leliefontein pump station has hydropower potential, which led Zutari’s design team to create a station that would have the ability to pump water and generate electricity using the same pumps. The pump-as-turbine (PAT) station is considered a first of its kind in South Africa. While using pumps as turbines is not a new concept, Leliefontein uniquely uses the same set of pumps to pump water and generate electricity by reversing flow through the pumps.
The project won ‘The Most Outstanding Project in Water Engineering’ award at the South African Institution of Civil Engineering (SAICE) National Awards in 2018 as well as a Consulting Engineers South Africa (CESA) AON Engineering Excellence Award in 2019 in the category “’Projects with a value of less than R50 million”’.
“Leliefontein is a true marriage between the civil, mechanical, and electrical engineering disciplines, and serves as an example of how municipalities can use low- cost, off- the- shelf equipment like centrifugal pumps and induction motors to generate clean power using potential energy in their existing infrastructure,” says Jacobus Kriegler, Zutari Professional Civil Engineer.
The challenge that the project team faced was that the pump station was only required for only two weeks of the year. The installation would be under-utilised with the risk of the premature failure of mechanical equipment. This led the team to solve the under-utilisation challenge by using the same pumps to pump water and generate electricity. As the main purpose of the installation was to pump water, the challenge faced by the team was building an efficient pump station with a minimal cost of conversion to generation.
While using pumps as turbines is not a new concept, Leliefontein uniquely uses the same set of pumps to pump water and generate electricity by reversing flow through the pumps.
To overcome this challenge, the team designed the pump station before making cost-effective alterations to the design for generation purposes. A further challenge was that the pump-as-turbines (sized for efficient pumping) were unable to generate power with available hydropower potential. The solution was to reduce the speed of the pump-as-turbines via the electrical control system.
The resulting pump-as-turbine station was achieved through the innovative use of active front-end variable speed drives to lower the speed of the PATs to generate electricity at the available hydropower potential, a series of actuated valves, and some creative pipework. The power generated at the station is fed back into the municipal grid, offsetting the power consumed during pumping. The PAT conversion cost only R3 million extra to a contract value of R30 million. The estimated annual generation is 320 MWh, which translates to 44 days of free pumping.
“The power generated at Leliefontein can be offset against the power that the Drakenstein Municipality would have had to purchase from the electricity public utility. It not only reduces the Municipality’s environmental impact through the consumption of renewable energy, but it also has a social impact because the client can invest the money saved by utilising the renewable free energy, back into the community through the delivery of services. We commend the client on their future-ready pump-as-turbine station,” says Kriegler.
*The Aurecon Africa business has been officially renamed Zutari as at 21 July 2020. Zutari acquired Aurecon Middle East on 20 November 2020.