Solar Hot Water Systems

The sun's heat has been used for decades to heat water for homes and businesses. At the turn of the 20th century, solar heated water systems were common in Southern California. Some countries have made their use mandatory. For example, most homes in Israel have solar hot water systems.

More than one-half million solar hot water systems have been installed in the United States, mostly on single-family homes. The majority of these systems are used to heat swimming pools.

Solar thermal system on a house roof

Photo by Paul Norton, NREL 13529

Typically, a homeowner relying on electricity to heat water could save up to $500 in the first year of operation by installing a solar water heating system. The savings over time increases due to increasing electricity rates. The average solar heating system pays for itself in four to seven years.

Roof-mounted solar hot water systems are often designed to look like skylights, making them more pleasing in appearance to homeowners and their neighbors.

The cost of solar water heating systems declined by 30 percent between 1980 and 1990. Further cost reductions will not be as dramatic, but prices will continue to decrease as demand increases and manufacturers take advantage of economies of scale.

How it works

In the animation above, cold water from the home's regular water line is being pumped to the roof (blue line) where it enters the thermal energy collector. Sunlight strikes the collector, and the sun's heat warms the water. The heated water comes back into the home or business.

Inside, the warmed water from the roof is collected in a "solar" tank, which has temperature sensors and other mechanisms. The warm water from the solar system then goes into the regular hot water system. Because the regular hot water system (either electric or gas heated) is heating warmer water, you don't have to heat it as much as if it were plain cold water. If no one turns on a hot water tap, the water is circulated back to the roof to be heated even more. During the night, the system can be set up so that water is not pumped to the roof, preventing heat loss to the cool outside air.