| Vol. 8 | No. 2 | Spring 2006 |
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A Cleaner Water Heater |
According to the Department of Energy, water heating accounts for about 15 percent of a household’s annual energy use. And since most American homes rely on fossil fuels to heat water, this necessity of life contributes to air and water pollution as well as global warming. Fortunately, solar water heaters can offset between 50 and 100 percent of a home’s hot water needs—a plus for both pocketbooks and the environment.
No Shortage of Options
Different types of solar water heating systems all operate according to the same basic principle: energy from the sun heats air or a liquid circulating through a solar collector, which transfers the heat to a conventional water heater. The two most common types of solar collector for water heating are flat plates and evacuated tubes.
A flat-plate collector is an insulated, glass-covered box containing a dark-colored absorber plate and fluid-filled pipes. Sunlight is converted to heat when it hits the absorber plate; the heat is then transferred to the pipes, generating water hot enough for most household applications including space heating. Evacuated-tube collectors minimize heat loss by encasing the absorber plate and pipes within glass vacuum tubes; this provides higher water temperatures than flat-plate collectors (above 140 degrees Fahrenheit). Though this can be useful for colder climates or where higher water temperatures are required, it does result in a higher up-front cost.
If you plan to install a solar water heater, you’ll not only have to decide what type of solar collector your system will incorporate, but what type of fluid will circulate through the system. This choice is often influenced by the climate in which you live.
Direct systems, for example, use your home’s water as the means for transferring heat from the collector to the storage tank, and work best in temperate climates. Freezing temperatures typically call for indirect systems, which use air or, preferably, a nontoxic antifreeze solution to transfer heat. Pumps (which can also be solar-powered) are typically required to help circulate air or liquids through these systems, and a heat exchanger is required as well.
Money Well Spent
Depending on type and size, solar water heating systems typically cost between $2,000 and $6,000 (including installation), and can pay for themselves within 4 to 10 years. An average lifetime of 20 to 30 years ensures that these systems will continue to save homeowners money on energy costs for years to come. In addition, you might be able to take advantage of financial incentives such as rebates or tax credits to help reduce the up-front costs. Check the Interstate Renewable Energy Council’s online Database of State Incentives for Renewable Energy for a list of incentives offered by federal, state, and local agencies as well as utility companies in your area.
Even if you are not planning to buy a solar heating system, be sure your existing system is working as efficiently as possible. Insulating your water heater and hot water pipes, for example, and installing low-flow water fixtures will help reduce energy and water use. Replacing your conventional water heater with a more efficient model will lower your energy costs even further. Then, if you do decide to invest in a solar heating system, your needs might be met by a smaller system.
Also in this issue of Earthwise:
Dialogue
I’ve seen several different rating systems for vehicle emissions. How do they compare?
