‘Sand batteries’ could be a key breakthrough in storing solar and wind energy all year round. Solar energy stored in sand batteries could help get Finns through the long cold winter, which is set to be even tougher after Russia stopped its gas and electricity supplies. The new technology has been devised by young Finnish engineers Tommi Eronen and Markku Ylönen, founders of Polar Night Energy. This innovation could be used worldwide. Whilst a number of other research groups are testing the limits of sand as green energy storage, the pair are the first ones to successfully rig it to a commercial power station.