Solar Hot Water
Up to 25 percent of a household utility bill goes to heating water for washing clothes, dishes, and ourselves. A solar hot-water system can reduce those costs by two thirds — without using any fossil fuels or causing any pollution.
by Max Alexander
If you’ve ever felt warm water flow from a garden hose that’s been stretched across a sunny lawn, you know how solar water heating works. And if you’ve ever paid a fuel or electric bill, you can understand why using the sun’s rays to warm water is a good idea. Up to 25 percent of a household utility bill goes to heating water for washing clothes, dishes, and ourselves. A solar hot-water system can reduce those costs by two thirds—without using any fossil fuels or causing any pollution. You don’t even need to live in a sunny climate to take advantage of this infinitely renewable source of free power. Thanks to advances in solar-collector technology, these systems have become practical even in places where the sky is gray more often than blue.
a. flat-plate solar collector; b. expansion tank; c. pump; d. controller; e. storage tank; f. main supply; g. water heater; h. hot water for house
Illustration:: Harry Campbell
The basic setup consists of a heat-trapping solar collector sitting outdoors in an open, south-facing location—usually up on the roof—and a water-storage tank inside the house. In cold climates, a pump circulates an antifreeze-laced liquid through a closed loop of pipe connecting the rooftop array and the tank. A submerged coil inside the tank transfers the heat from the sun-warmed liquid to the household water supply. (In frost-free zones, potable water can be heated directly by the collector.)
Collectors come in two main types. The most popular are the so-called flat-plate collectors: insulated glass boxes with copper pipes attached to heat-trapping “absorber sheets.” Under ideal conditions, they can produce 150-degree water, well above the 125-degree water in a typical water heater. More efficient tube-type collectors encapsulate the absorber sheets and pipes in glass vacuum tubes for maximum insulating effect. They can heat water up to 200 degrees. And because tubes can capture heat when the sun is not directly overhead and even on cloudy days, you don’t need a big array to get a lot of hot water. The downside is that they cost twice as much as flat plates.
