Sign up to our free weekly IndyTech newsletter delivered straight to your inboxSign up to our free IndyTech newsletterAn 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 batter...