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Thursday, Nov. 2, 2006 09:03 pm

Cutting carbon dioxide emissions

One way is to use a solar-powered water heater

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Dear Earth Talk: I heard that using a solar-powered water heater in my home would reduce my carbon dioxide emissions significantly. Is this true? What are the costs? — Anthony Gerst, Wapello, Iowa

According to mechanical engineers at the University of Wisconsin’s Solar Energy Laboratory, an average four-person household with an electric water heater needs about 6,400 kilowatt hours of electricity per year to heat its water. Assuming that the electricity is generated by a typical power plant with an efficiency of around 30 percent, the average electric water heater is responsible for about 8 tons of carbon dioxide (annually, almost double that emitted by a typical modern automobile.

The same family of four, using either a natural gas or oil-fired water heater, will contribute about 2 tons of carbon dioxide emissions annually in heating water.

Surprising as it may seem, analysts believe that the annual total carbon dioxide produced by residential water heaters throughout North America is roughly equal to that produced by all of the cars and light trucks driving around the continent. Another way of looking at it: If half of all households used solar water heaters, the reduction in carbon dioxide emissions would be the same as doubling the fuel efficiency of all cars.

That may not be such a tall order. According to the Environmental and Energy Study Institute, 1.5 million solar water heaters are already in use in U.S. homes and businesses. Systems can work in any climate, and the EESI estimates that 40 percent of all U.S. homes have access to sunlight such that 29 million additional solar heaters could be installed right now.

Another great reason to make the switch is a financial one. According to the EESI, residential solar water-heating systems cost between $1,500 and $3,500 compared with $150 to $450 for electric and gas heaters. With savings in electricity or natural gas, solar water heaters pay for themselves within four to eight years. They last between 15 and 40 years — the same as conventional systems — so after that initial payback period is up, zero energy cost essentially means having free hot water for years to come.

What’s more, in 2005 the U.S. government began offering homeowners tax credits of as much as 30 percent (capped at $2,000) of the cost of installing a solar water heater. The credit is not available for swimming-pool or hot-tub heaters, and the system must be certified by the Solar Rating and Certification Corp.

According to the U.S. Department of Energy’s Consumer’s Guide to Renewable Energy and Energy Efficiency, zoning and building codes relating to the installation of solar water heaters usually reside at the local level, so consumers should be sure to research the standards for their own communities and hire a certified installer familiar with local requirements. Homeowners beware: Most municipalities require a building permit for the installation of a solar hot water heater in an existing house.

For Canadians looking to get into solar water heating, the Canadian Solar Industries Association maintains a list of certified solar-water-heater installers, and Natural Resources Canada makes its informative booklet Solar Water Heating Systems: A Buyer’s Guide available as a free download on its Web site.

For more information: U.S. Department of Energy, www.eere.energy.gov/consumer/; Natural Resources Canada, www.canren.gc.ca/

Send questions to Earth Talk, care of E/The Environmental Magazine, P.O. Box 5098, Westport, CT 06881 or e-mail earthtalk@emagazine.com.

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