Abstract: A heat storage unit using salt or a salt mixture. Heat is extracted from the unit by converting water to steam and a series of pipes is provided extending to different depths in the salt. The pipes extend to different heights at the top of the unit so that water first overflows into the pipe extending the shortest distance into the salt. This results in the salt in the unit solidifying from the top downwards, thereby obviating problems caused by molten salt migrating to spaces at the foot of the container caused by contraction of salt on solidification. A heating system uses several such units with electrical heating between the units and pumped circulation of the condensate from the generated steam. An alternative system uses steam generated in such units selectively to drive a turbine for refrigeration equipment in a cooling system or to heat the heat exchange medium in a heating system.