Harvest the Sun with Solar Water Heaters

Enlarge Image Image Gallery Closed-loop solar water heaters are appropriate for areas where temperatures sometimes dip below freezing. Illustration Courtesy Energy Savers

Barb and Joe Gordon were delighted the day they had a solar hot water heater installed on their suburban Chicago home, boosting their energy independence and helping to create a cleaner world. Now when they use hot water, they take pleasure in knowing it is heated by the sun. The Gordons estimate that their 64 square feet of solar collectors heats 70 percent of the hot water the family of four uses annually, requiring their backup natural gas hot water heater to fire up infrequently.

Conventional hot water heaters are responsible for up to 25 percent of a home’s total energy use, so a solar hot water heater can significantly reduce a house’s carbon footprint and energy bills. In most residential installations, a separate solar hot water storage tank feeds a conventional natural gas, electric or propane hot water heater, which serves as a backup if needed. This ensures the home will never be without hot water—even after a few cloudy days. When quality components are used, systems can last 20 to 30 years and require little maintenance. Three main types of solar collectors are typically used for residential applications.

• Flat plate collectors are insulated, weatherproof boxes that contain a dark absorber plate covered with a sheet of glass.

• Evacuated tube panels contain rows of glass tubes connected to a header pipe. Their high efficiency makes them ideal for high-temperature or space-constrained applications.

• Integral collector-storage systems, also known as ICS or batch systems, feature one or more black tanks or tubes in an insulated box. After passing through the solar collector, preheated water continues on to a conventional backup water heater. These systems should only be installed in mild-freeze climates because outdoor pipes are prone to freezing.

Installing a Solar Water Heater

To determine if your home is a good candidate for solar water heating, also known as solar thermal, first determine your property’s solar exposure. It’s ideal to have unobstructed midday sun throughout the year, but remember that the panels don’t have to be mounted on the roof. They can be mounted as an awning, on the garage, or even in the yard, though this may add to the installation cost.

In the Northern Hemisphere, panels are typically mounted facing south at an angle 10 degrees greater than the latitude of the location. Contractors usually follow this general guideline to calculate the space required for a solar water heating system, according to the U.S. Department of Energy: For two household members, you will need 40 square feet of collector area. For every additional person, add 8 square feet if you live in a sunny area; add 12 to 14 square feet per additional person if you live in a cloudy or unpredictable climate. It is also necessary to have 2 or 3 square feet for a solar storage tank, ideally located near the backup hot water heater.