If successful, Gravitricity says its technology “could breathe new life into former mining communities.”

The new funding will enable the company to start building a small scale demonstrator later this year, “and find a site to install a full-scale prototype by 2020.”

Gravitricity says it is “now on the look-out for investors, including those who can bring mining experience to the team, and suitable shafts to trial the technology.” And once it has proven the technology in old mines, it then plans “to sink new shafts to store energy wherever it is required.”

“So far there is a lot of focus on batteries, but our idea is quite different”, says Gravitricity managing director Charlie Blair. “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.”

Unlike batteries, the Gravitricity system can operate for decades without any degradation or reduction in performance, Blair notes. The idea of using gravity to store energy is of course not new, says Blair, it is for example used in pumped storage schemes. “The difference is we don’t need a mountain with a loch or lake at the top, and we can react much faster.”

He says the biggest single cost is the hole, and that is why the start-up is developing its technology utilising existing mine shafts, both in the UK and also in South Africa.

As the technology advances, the cost of drilling will reduce significantly and make it feasible to sink purpose built shafts.