Is Solar-thermal Hot Water for You?

Roof-top solar panels that create hot water with sunshine significantly reduce energy bills and are relatively easy to install and maintain.

The North American Board of Certified Energy Practitioners certifies solar-thermal installers. Image: Heliodyne

We Americans take our hot water for granted — we love our soaker tubs, and many of us just can’t start the day without a vigorous shower. But it’s not free. According to the U.S. Department of Energy, on average we spend about $308 per year, per household, just to have hot water ready at the twist of a faucet handle. But you could slash that figure in half, or more, with a solar-thermal system — a proven renewable-energy technology that enables the rays of the sun to heat your home’s hot-water supply.

The fuel is free

Both solar-thermal systems and more costly solar-photovoltaic panels—which use the sun to generate electricity—can make a significant dent in your utility bill. But with a solar-thermal system, instead of generating energy, you’re saving it.

“When compared to solar-electric panels, it is a lower-cost option,” says Monique Hanis, a spokesperson for the Solar Industries Association. “A system for a home would run anywhere from $4,000 to $6,000, and that could take care of a good chunk of your hot-water needs.”

Those ballpark figures don’t include the across-the-board federal tax credit that knocks 30% off the cost of a system, plus there are additional state and local-government incentives that can trim set-up costs even more. (Check the Database of State Incentives for Renewables & Efficiency for relevant programs in your area.) Maintenance is minimal, and collectors should last for 20 years or more.

How solar-thermal works

All solar-thermal systems feature glassed-covered boxes or sets of tubes that contain fluid-filled piping. The systems can be divided into two basic categories—direct and indirect.

In an indirect system, a pump continually circulates an antifreeze solution between the collector mounted on your roof and a heat-exchanger coil located inside your home’s hot-water tank. A pump circulates the antifreeze solution between the solar panel—where the sun heats it—and the coil, where it raises the temperature of the water in the tank.

The second type of solar-thermal system, called a direct system, circulates household water directly through the solar collector. This setup is only appropriate for regions, such as Hawaii and Florida, that don’t experience winter freeze-ups.

Either type of thermal collector is so efficient that it will produce hot water even on a cloudy day—though a snowfall will bury and temporarily disable a collector until warmer temperatures melt the snow off.

How much you’ll need

A solar contractor/installer will evaluate your property’s potential for capturing solar radiation throughout the year, but your house is likely a good candidate if one side of its roof faces south, without too much shading from tall trees and structures. A pair of 4-by-8-foot collectors will significantly reduce the cost of heating hot water for a family of four.

How much you’ll save depends on where you live. The National Renewable Energy Laboratory has researched the degree to which a solar-thermal system can reduce a homeowner’s energy bill in various regions of the country. The lab expresses this savings via a rating known as a “solar fraction.”

Put simply, a solar fraction is the percentage of a home’s water-heating energy needs that could be met with a rooftop collector. For example, a solar fraction of 60% means that the solar-thermal hot water system would reduce the amount of energy a home used to heat hot water by 60%. In Harrisburg, Penn., Albany, NY, and Eugene, Ore., the solar fraction is 50%. In Fort Worth, Texas, and Tampa, Fla., it’s a whopping 75%.

Researching solar-thermal collectors

Last fall, the U.S. Department of Energy added solar-hot water systems to its EnergyStar program. You can browse approved solar water heaters on the Energy Star web site, and discuss which model best suits your needs with an installer. Bear in mind that solar-thermal collectors are not do-it-yourself projects. The North American Board of Certified Energy Practitioners certifies solar-thermal installers. As of late 2009, the group’s web site lists 97 professionals across the country who sell, install, and service the systems.

If you’re interested in saving energy and harnessing the free power of the sun, a solar-thermal water-heating system is an attractive option.