If circumstances allow, Cape Town and Johannesburg are both able to spare their citizens from stage 1 load shedding.
The City of Cape Town and City Power in Johannesburg announced last week that their residents would once again not be affected by stage 1 load shedding, thanks to spare generation capacity.
This is not the first time the City of Cape Town has been able to prevent stage 1 load shedding from affecting its residents. On 21 June, both the Cape Town and Johannesburg metropolitan municipalities were able to avert the stage 1 load shedding. Cape Town said this was thanks to its Steenbras hydroelectric pumped storage scheme; while City Power explained that it has numerous measures in place to try and avoid load shedding.
Steenbras was commissioned on 8 August 1979 and is owned by the City of Cape Town. Each of its 4 generating units can act as either a pump motor or a turbine generator.
“Surplus national generating capacity is employed to utilise relatively low-cost off-peak electricity available at night to pump water from a lower to an upper storage reservoir,” said the City of Cape Town.
During periods of peak demand in the day, the water is released back to the lower reservoir, generating electricity as a hydroelectric power station would.
“Steenbras is used for the purpose of removing peaks. In winter, these peaks usually fall between 08:00 and 10:00 in the mornings and 18:00 and 20:00 in the evenings.”
The City may have spare capacity at times outside the peak periods and at times when these peaks are low, but it warned it won’t always be able to prevent a stage 1 blackout.
“An assessment is done prior to implementing any stage of load shedding,” it said.
Outside Steenbras, the City does not have other power plants that generate excess capacity.
“The City has the Roggebaai Gas Turbines (42MW) and the Athlone Gas Turbine (36MW) – both of which are also dispatched for removing peaks but for much shorter periods.”
However, these use more expensive fuel (Aviation Jet-A1,) and after maximising the output of Steenbras are not used as much as the hydroelectric dam.