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 their water. Assuming
the electricity is generated by a typical power plant with
an efficiency of around 30 percent, it means that the average
electric water heater is responsible for about eight tons of
carbon dioxide (CO2) annually, which is 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 two tons of CO2 emissions
annually in heating their water.
Surprising as it may seem, analysts believe that the annual total
CO2 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 is: If half of all households used solar water heaters, the
reduction in CO2 emissions would be the same as doubling the
fuel efficiency of all cars.
And that might not be such a tall order. According to the Environmental
and Energy Study Institute (EESI), there are 1.5 million solar
water heaters already in use in U.S. homes and businesses.
can work in any climate and EESI estimates that 40 percent of
all U.S. homes have sufficient access to sunlight 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 to $150 to $450 for electric and
gas heaters. With savings in electricity or natural gas,
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 United States began offering
homeowners tax credits of up to 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 Corporation.
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 onto an existing