Active solar water heaters use pumps, often powered by a solar electric module, to circulate water or heat-transfer fluid through heat-absorbing solar thermal collectors.
Open Loop Active Systems
Open loop active systems heat the water supply directly. Circulation of water through the solar collector is accomplished via a small circulation pump (often powered by a solar electric module) mounted on a solar storage tank. The solar pump is activated by a differential thermostat controller (solar sensor) that senses when heat is available in the solar collectors. The solar-heated water is stored in a storage tank that connects to the existing gas or electric water heater. As hot water is used, the preheated water is pumped into the conventional heater.
The solar collectors and feed lines are protected from freezing by automatic drain down controls which allows the water in the pipes and panels to fall safely back out of the solar collectors and feed pipes.