The industrial-scale sand battery in Finland's Pornainen can cover almost one month of the town's heating demands in the summer and as much as one week in the winter.Polar Night EnergyA small town in southern Finland has turned to the world's largest commercial sand battery to fix what many see as the most critical problem facing renewable energy: intermittency.Standing at 13 meters tall and 15 meters wide, the eye-catching facility uses 2,000 metric tons of crushed soapstone to store clean ener...