Grid interaction analysis of solar water heating photovoltaic-thermal (PV-T) systems with thermal storage tanks and electrical auxiliary heaters

Photovoltaic-thermal (PV-T) solar water heating systems are commonly envisioned as a combination of regular solar water heaters and grid-connected photovoltaic (PV) systems. Nevertheless, the PV circuit can be left in open-circuit mode to increase the effective thermal absorption or the PV electricity generated can be used to heat the storage fluid through a secondary electrical heating element. Annual dynamic simulations using representative solar water heating system sizes and representative PV-T technology were conducted for these three configurations. The purpose was to indirectly determine how they would perform on a temporary basis if used on demand by grid-operators as part of the renewable energy resources at their disposal. The results show that the use of local PV electricity to heat the storage fluid caused the shortest pump running time and lowest auxiliary energy consumption of all cases considered. In light of these results, it is reasonable to state that this solution is more efficient than disabling the PV array to increase the heat available at the collector. The practical implications of a potential application of these methods were also discussed.