South Africa’s own renewable rollout is a perfect example of this, as the numbers for the latest solar power project testify. The 100MW ACWA Power SolarReserve Redstone Solar Thermal Power Plant began early works in February in the Northern Cape.
Completion is set for October 2023, the concentrated solar power (CSP) plant is expected to electrify about 210,000 South African homes during peak demand periods. The facility will have a purchase power agreement (PPA) for 20 years with Eskom, starting on completion of the project. The total project cost is estimated at R11.5bn.
“Not only will it be sub-Saharan Africa’s first CSP molten salt tower, but it will also be the largest of its kind in sub-Saharan Africa, second only to Morocco’s 150MW NOOR III CSP, also commissioned by ACWA, says Bernard Geldenhuys, senior transactor in the power and infrastructure team at Investec Bank, which has been closely involved in the project since 2018, providing senior debt worth R750m, foreign exchange and interest rate hedging, as well as other facilities.
The Redstone project will also be the CSP with the largest storage capacity on the continent, as well as its lowest tariff in South Africa. “It’s the first renewable energy independent power producer procurement (REIPPP) project to provide ancillary services (grid stabilisation services) to Eskom, at no additional cost. And it’s the largest REIPPP project, in terms of total investment,” he says.
A CSP molten salt tower, as its name suggests, is a 250-metre tall central receiver tower which uses molten salt as the heat transfer fluid and storage medium. It differs from CSP molten salt parabolic trough plants, in that the solar energy reflected from the solar field directly heats up the molten salt contained in the central receiver positioned on top of the tower. A CSP molten salt parabolic trough plant uses thermal oil, which is heated by the reflected solar energy and in turn heats up the molten salt in the storage system. This intermediate heat transfer process in parabolic trough systems causes significant energy losses and therefore is a less efficient plant.
Molten salt technology allows solar energy to be stored for dispatch during the evenings and early mornings, when demand among households is usually greater and the sun does not shine. Advances in solar field control systems and improvements through scale have made this an increasingly viable alternative to coal-powered plants.
“In the Redstone CSP Tower case, the thermal storage lasts for 12 hours, making it a truly dispatchable facility,” says Geldenhuys.
The rollout of renewable projects should not only assist the transition to low and zero carbon emissions but will also benefit regions such as the Northern Cape economically, through job creation and enterprise development. “This project is estimated to create over 2,000 jobs over the life of the plant,” he says.
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