A renewable water-heating option that is becoming more common is to heat water using electricity from a grid-tied photovoltaic (PV) system. As the cost of PV modules has dropped in recent years and heat-pump water heaters have improved in performance, this strategy has become more economical and efficient. Some people even use PV electricity with well-insulated electric-resistance storage-type water heaters.
PV water heating eliminates pumps, pipes vulnerable to freezing, and the risk of collector stagnation. PV systems have no moving parts, so there is little to break down or require maintenance, and the same PV system can satisfy a wide range of other needs. Plus, under a net-metering agreement with a grid-tied PV system, any surplus electricity is credited to your bill. With a standard solar water-heating system, once the water in the storage tank is up to temperature, the system shuts down and any “excess” heat has to have a means of being dissipated.