Method and apparatus for storing heat in industrial systems where large sources of stored energy are called upon to meet a work load, storing the heat content of a hot working fluid by using the hot working fluid as a heat transfer fluid in vapor form and depositing its heat content on a heat storage medium and then removing the cooled and condensed liquid phase of that heat transfer fluid, and when hot working fluid again is needed, the liquid heat transfer fluid is returned to the heated storage medium and is reheated as it passes through the hot storage medium and then is returned to the working system to be used as a hot working fluid.