An abandoned mine in Finland is set to be transformed into a giant battery to store renewable energy during periods of excess production.
The Pyhäsalmi Mine, roughly 450 kilometres north of Helsinki, is Europe’s deepest zinc and copper mine and holds the potential to store up to 2 MW of energy within its 1,400-metre-deep shafts.
The disused mine will be fitted with a gravity battery, which uses excess energy from renewable sources like solar and wind in order to lift a heavy weight. During periods of low production, the weight is released and used to power a turbine as it drops.
I was thinking that you would need increasingly beefy motors and cables/cranes as the size of the rocks scales. But for a reservoir, you could use the same pump over a longer period of time to store much more energy. It’s also easy to utilize a body of water with a volume much greater than the volume of a vertical cylinder.