Given their intermittent heat generation characteristics, many hydronic-based renewable energy systems require thermal storage. Examples include solar-thermal systems and biomass boilers. Thermal storage also is used in heating systems supplied by off-peak electricity and micro-combined heat and power systems.
The temperature of the thermal storage tank can vary over a wide range. If supplied by a solar collector array and after two or three sunny days with minimal loading, the tank temperature could be upwards of 180° F. These temperatures also are possible at the end of a tank “charging” cycle from a biomass boiler, as well as in off-peak electric thermal storage and MCHP systems.