Solar water heating is more often found in hot, sunny climates such as Arizona or Hawaii than Western Washington, where we have a shorter solar season. A solar water heater is mounted to a home’s roof to take advantage of the sun’s radiation to heat or preheat water before use in the home. A closed loop system of heat transfer liquid is mounted in a collector panel below the tank and is heated by the sun.
The hotter liquid rises in the system, which comes into contact with the domestic water. The heat energy is then transferred to the water in the tank. Once the heat energy is released into the tank, the liquid continues flowing back along the loop, into the collectors, and the cycle continues. If there is inadequate solar heat gain and the water doesn’t reach the desired temperature, a standard electric or gas water heater is used to add heat until the water reaches the desired temperature. Many systems are passive, closed loop systems, but some require a small circulating pump. There are many various technologies used in solar water heating worldwide.