Storing renewable energy in mineshaft weights may be cheaper than using batteries

21st October 2019 | Commercial Energy

A system that stores excess renewable energy in weights suspended above disused mineshafts could be cheaper than batteries according to a report by independent analysts at Imperial College London. The proposed system received a 650,000 grant from Innovate UK last year, and patent owner Gravitricity has teamed up with Dutch winch specialist Huisman to build a 250kW scale prototype.

“Our idea is very simple. We use excess energy to lift a massive weight or weights to the top of a shaft. These can then be stacked and released when required, delivering energy rapidly back to the grid. The beauty of this is that this can be done multiple times a day for many years, without any loss of performance. This makes it very competitive against other forms of energy storage – including lithium ion batteries,” said Gravitricity managing director Charlie Blair.

Renewable Energy

Up to 24 weights totalling 12,000 tonnes can be stacked in a mine shaft to capture power and can then be released “with sub-second response time.” “The climate emergency means we need to find new ways to capture and store green energy so we can use it when we need it,” Blair added.

While the developers will target former mine shafts initially, in the longer term they plan to sink purpose-built shafts wherever required. They are currently in discussion with mine owners in the UK, South Africa, Finland, Poland and the Czech Republic. The analysts at Imperial Consultants said that Gravitricity’s multi-weight system offers a better long-term cost of energy storage than batteries or other alternatives.

The report says the Gravitricity system performs particularly well in the “peak-shaving” market, a service which ensure the balancing of electricity demand and supply during peak demand periods to reduce the strain on power infrastructure. This typically requires a storage system to discharge for two to six hours, twice a day. The analysis was based on a 10MW maximum capacity delivering 24MWh – this translates to around 2.5 hours discharge duration at maximum power output.

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