As in all hot water systems, the storage tank’s task is to balance peak demand and charging power in supplying hot water and in solar systems additionally compensates for time differences between solar energy supply and hot water requirements. It typically features a heat exchanger at the bottom, in which the transfer medium from the collector (usually a water-antifreeze mixture) transfers the solar energy from the collector to the storage tank’s content.

Where required, the upper part of the storage tank is additionally heated by a conventional heating system, so that the hot water taken from the upper part is always at the required target temperature, irrespective of available solar energy. Larger solar systems use several storage tanks connected in series, of which the last one is used for reheating.