How Do Solar Hot Water Panels Work?

Heat, Not Electricity

A general misconception about solar hot water heaters is that their panels are photovoltaic, or meant for generating electricity. No solar water heater works this way. Electric water heaters are very costly to run, and using photovoltaic electricity to heat water would require a very large array of photovoltaic panels. Instead, solar water heaters work by collecting and concentrating the heat of the sun, a more efficient means of heating water.

Collecting Sunlight

Designs for a solar water heater's collection panels vary in sophistication, but the typical one is very simple: a glass-paneled, insulated box on a black backing. Another design is the evacuated tube panel, which uses several layered water pipes in place of the glass panel. The outer pipes are a specially coated glass absorber that replaces the outer glass panel. The inner pipe contains the water to be heated. This design has the advantage of being less influenced by outside air temperature. A parabolic mirror for concentrating sunlight onto the collecting units is an option that can be added to the design.

Water and Pumping

Some solar water heaters use convection to circulate water from the tank to the heater and into the home. Others have a small electric pump. However, when there is an electric pump, it draws power by being plugged into the house or building--not from a photovoltaic solar panel.

The Tank

The next most important element after the solar panels is the water tank. This is heavily insulated--more than most conventional water heaters as they are known in the United States--because they're kept outside and adjacent to the solar heating panels.

Resources

• DOE: Solar Water Heaters