A method of storing excess thermal energy in a reservoir containing molten salts. Different types of salts are used, e.g. sodium nitrate or potassium nitrate, with a melting point of 250 °C and higher. Heat is stored in the reservoir and can later be transferred in a heat exchanger to water to convert it into steam that will drive the turbine. The molten salt energy storage technology has so far been used in concentrating solar power plants, where the heat transfer medium reaches temperatures of around 500 °C due to heating from concentrated sunlight.