Our big holes may come in handy after all


Our big holes may come in handy after all

Old South African mines could get a new lease of life as hi-tech green energy stores

Cape Town bureau chief

British energy start-up Gravitricity, which has just received a £650,000 (R10.1-million) government grant for its plan to harness the power of gravity to store renewable energy, says it is keen to talk to South African mining operators.
The technology could breathe new life into former mining communities, said managing director Charlie Blair.
“Gravitricity uses a heavy weight – up to 2,000 tons – suspended in a deep shaft [up to 1,500m] by cables attached to winches,” he said.
“When there is excess electricity, for example on a windy day, the weight is winched to the top of the shaft ready to generate power.“This weight can then be released when required – in less than a second – and the winches become generators, producing either a large burst of electricity quickly or releasing it more slowly, depending on what is needed.”
The idea is similar to pumped storage systems, such as the one opened at Steenbras in 1979 to supplement Cape Town’s electricity supply during periods of peak demand.
“The difference is we don’t need a mountain with a loch or lake at the top, and we can react much faster,” said Blair.
Unlike batteries, the system could operate for decades without any degradation or reduction in performance. The biggest cost was the hole, hence the interest in mine shafts in South Africa and the UK.
“We are keen to speak with mine operators in South Africa to understand how we might work together,” said Blair.The R10-million injection would enable the company to start building a scale demonstrator this year and it is shortlisting a number of disused mine shafts for the first full-scale working prototype in 2019/20.
Gravitricity’s website said while the weight could be used on its own to generate power, “the energy storage capacity of the overall system can be much increased when the shaft is used as a pressure vessel for compressed air.
“This involves adding a pressure-tight ‘lid’ to the top of the shaft and lining the shaft to prevent leakage. The ground provides the bursting resistance other than at the very top of the shaft. The winches and generators are normally contained in the pressurised space so that only electrical cables need to penetrate the pressure vessel walls.”

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