A slight tilt of the collectors is required in order to allow complete drainage. A sight glass attached to the drain-back reservoir tank shows when the reservoir tank is full and the collector has been drained. In this particular system, distilled water is recommended to be used as the collector loop fluid- transfer solution. Using distilled water increases the heat transfer characteristics and prevents possible mineral buildup of the transfer solution. When the sun shines again, the pump is activated by a differential controller.
Water is pumped from the reservoir to the collectors, allowing heat to be collected.
The water stored in the reservoir tank circulates in a closed loop through the collectors and a heat exchanger at the bottom of the solar tank. The heat exchanger transfers heat from the collector loop fluid to the potable water in the solar tank. Cold water flows progressively through the collector where it is heated by the sun. Hot water is drawn from the top, which is the hottest, and replacement water flows into the bottom. This system is simple because pumps and controllers are not required.