The small photovoltaic panel, mounted in the sun next to the collector, powers the circulating pump directly (no batteries) and just runs when there is enough sun to make hot water. Totally self-sufficient and completely solar powered.
This system uses a microprocessor in the Differential Controller to determine when the water in the solar collectors is warmer than the tank water. Sensors on both the tank and on the collectors control the operation of the circulating pump. This system is usually connected to the standard AC electric power supply (mostly the state owned ICE in Costa Rica).