District heating networks, an important part of the energy transition for buildings, need a way of storing intermittent wind and solar power. But water tanks have limits: they take up a lot of space, and have a low thermal energy storage density (limited by the 100°C boiling point). Molten salts have a much higher storage density (regular table salt has a melting point of 801°C), but a melting point that is too high is not safe where ordinary … [Read more...]