Because they generate heat intermittently, renewable energy heat sources such as solar thermal collectors and pellet boilers require thermal storage tanks. So do storage-based systems using off-peak electricity, or micro combined heat and power (MCHP) generation.
The temperature of the thermal storage tanks in these systems can vary over a wide range. If supplied by a solar collector array, the tank temperature could be upwards of 180° F following a couple of sunny days with minimal heat demand. These temperatures are also possible when a pellet boiler finishes “charging” its thermal storage tank.