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Letting The Sun Shine In

Solar hot water systems can be an efficient way to lower energy costs. Although the basis of the technology is simple—sunlight shining on a dark-colored tank or collector—making it useful calls for solutions for details like how to circulate the water and how to keep it from getting too hot or too cold.

Controlling water movement is fairly simple. A passive system uses the pressure of the water within the home’s existing plumbing system. An active system adds circulating pumps and other control devices.

Controlling heat gain or loss (during cold weather or overnight) is more complicated. In a direct (“open loop”) system, household water circulates through the solar collectors and into the home. Most direct systems can be used only in mild climates that do not experience freezing conditions.

In an indirect (“closed loop”) system an antifreeze solution circulates through the collector. A heat exchanger then transfers the heat in the antifreeze solution to the household water supply. Indirect systems can be used in any climate, and are recommended for Kentucky.

The most efficient systems also include a drainback feature or other technology to prevent the water from boiling or freezing during weather extremes.

Heating domestic water typically accounts for about 20 percent of a household’s energy bill, or $100 to $300 per year. A well-designed solar water heating system can nearly eliminate that energy use. Special systems to heat swimming pool water are another energy-saving option.

The U.S. Department of Energy provides an online tool to estimate the initial costs and payback period for a solar hot water system—learn more at

Your local electric cooperative can also help you calculate your potential savings. Then check the Database of State Incentives for Renewables and Efficiency for your locale at for any available incentives.
—NRECA Cooperative Research Network

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