Gravitational Energy Storage

"How UK's disused mine shafts could be used to store renewable energy":

The surprising new source of “gravity energy” is being developed by Gravitricity, an Edinburgh-based startup, which hopes to use Britain’s old mines to make better use of clean electricity at half the cost of lithium-ion batteries.

Gravitricity said its system effectively stores energy by using electric winches to hoist the weights to the top of the shaft when there is plenty of renewable energy available, then dropping the weights hundreds of metres down vertical shafts to generate electricity when needed...

Charlie Blair, Gravitricity’s managing director, said: “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.”