What's So Hot About Solar Water Heaters?

I

nstalling a solar water heater would seem to be the perfect green addition to a home: once it's in place, you'll never use another unit of gas or electricity to heat water for your home, right?

Well, wrong. Solar water heaters will certainly reduce the amount of energy required to provide hot water for your home by 50 to 80 percent, according to the U.S. Department of Energy. Although they aren't up to the task of meeting all of the hot water needs for a typical house, solar water heaters can be a very worthy investment.

How They Work
There are two main types of solar water heaters used for residential purposes. Both obviously use the sun to heat water, but they do so in different ways. A direct circulation system heats the water directly and then pumps it into a conventional water heater. This is the more efficient of the two types. However, direct circulation systems can only be used in mild-freeze areas because a moderate to severe freeze would cause the tubes the water is heated in to burst. Indirect circulation systems heat a transfer fluid--generally something similar to the antifreeze used in cars--which is then pumped through a heat exchanger where the heat is transferred to the water. The heated water is then pumped into a conventional water heater. Indirect circulation systems can be used in any climate.

An Enhancement, Not a Replacement
You probably noticed that both types of solar water heater pump their heated water into a conventional water heater. This is for two reasons. The first is that solar water heaters often can't get water as hot as it needs to be. They also don't work as well on cloudy days, or at night, or when outdoor temperatures are particularly low. So a solar water heater won't suffice as a replacement for your existing water heater. What it will do is preheat the water that goes into a conventional water heater. The result is that only one-half to one-fifth as much gas or electric energy is needed to finish heating the water, a dramatic increase in efficiency.

Investment Versus Return
Solar water heaters cost between $1,000 and $3,500, but they immediately begin paying for themselves via lower utility bills. Just how long it takes to turn a profit depends on a number of factors, including where you live (solar water heaters operate best in warm climates), how much hot water you use, and the price of energy (the more prices go up, the quicker solar heaters pay for themselves). In general, you can expect a full return on your purchase price in two to seven years. Everything after that is money in your pocket.