Abandoned South African mines could become giant batteries to fend off load shedding if a UK company has its way

Business Insider SA

News analysis

  • A UK company has a novel but simple idea for storing electricity: by using giant weights hung in disused mine shafts.
  • Gravitricity's early numbers suggest its winch system can support electricity grids much more cheaply than lithium batteries.
  • The company has its eye on South Africa, which lacks the water for pumped storage – but has a lot of really deep holes in the ground.
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If UK company Gravitricity has its way, abandoned mine shafts in South Africa could become giant batteries in the next few years, helping to stabilise the Eskom grid and stave off load shedding using nothing more than weights and winches.

Eskom implemented stage 4 load shedding on Monday. It is likely that load shedding will continue for the rest of this week.

Gravitricity's plan is novel but simple: attach some really heavy weights – anything from 500 to 5,000 tonnes – to winches planted at the mouth of a deep hole. When you need electricity, let the weights drop down the hole and use the motion to generate power. When you want to store electricity, haul the weights back up to the top again.

Such a system could be used to store power from renewable sources – such as solar farms – for later use, the company says.

It could also be used to guard an electricity grid from sudden spikes in demand, or an unexpected outage at a major generator. Giant lithium-ion batteries are currently favoured for such applications, but one study suggests a gravity system would cost about half as much as such batteries, while being able to deliver electricity quickly, with full power kicking in within one second.

That makes such a system potentially attractive in places with lots of sun and a need to guard against unexpected trouble from base-load generators.

It is also, theoretically, attractive in places that have really deep holes in the ground – many of the deepest in the world, in fact – and where those holes are being abandoned.

Gravitricity is already in talks with mines in and around Europe, as well as in South Africa, though it has not said which companies it is dealing with, or how soon it expects to have a commercial installation operational. But the company intends to start scaling up from demonstration models in 2020, and has raised nearly 90% of a R4.6 million crowd-funding target to build a 250 kilowatt unit soon.

This is how Gravitricity plans to turn disused mine shafts into giant backup batteries for electricity grids.

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