Back-up/supplemental heater

Each solar thermal system must have a back-up heating supply. Often gas or electricity and sometimes biomass (wood) are used as a heat source. Due to the 20+ year lifecycle of heating systems, including solar thermal systems, possible changes in energy supply options should also be considered.

It is important to control the solar energy system to provide the required temperature to the building energy systems. So if the domestic hot water must be 140 °F (60 °C), the heat transfer fluid must be hot enough to deliver that temperature. If it is not, then the supplemental heating system will be energized causing additional energy costs to occur. Running the supplemental heater is often very inefficient for this use since it would be cycling on/off and would not be operating at its normal firing rate.