Before you buy and install a solar water heating system, you need to first consider your site’s solar resource. The efficiency and design of a solar water heating system depends on how much of the sun’s energy reaches your building site.
Solar water heating systems use both direct and diffuse solar radiation. Even if you don’t live in a climate that’s warm and sunny most of the time—like the southwestern United States—your site still might have an adequate solar resource. If your building site has unshaded areas and generally faces south, it’s a good candidate for a solar water heating system.
Your local solar system supplier or installer can perform a solar site analysis.
Source: EERE, U.S. Department of Energy