Solar water heaters—also calledsolar domestic hot water systems—can bea cost-effective way togenerate hot water for your home. They can be used in any climate, and the fuelthey use—sunshine—is free.
How They Work
Solar water heating systems include storage tanks and solar collectors.There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don’t.
Most solar water heaters require a well-insulated storage tank.Solar storage tanks have an additional outlet and inletconnected to and from the collector. Intwo-tank systems, the solar water heater preheats waterbefore it enters the conventional waterheater.In one-tank systems, the back-up heateris combined with the solar storage in one tank.
Three types of solar collectorsare used for residential applications:
Glazed flat-plate collectors are insulated, weatherproofed boxes that contain adark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors—typically used for solar pool heating—have a dark absorber plate, made of metalor polymer, without a cover or enclosure.
Integral collector-storage systems
Also known as ICS or batch systems, they feature one ormore black tanks or tubes in aninsulated, glazed box. Cold water firstpasses through the solar collector, which preheats the water. The waterthen continues on to the conventional backup water heater, providing a reliablesource of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.
Evacuated-tube solar collectors
They feature parallel rows of transparent glasstubes. Each tube contains a glass outertube and metal absorbertube attached to a fin.The fin’s coating absorbs solarenergy but inhibits radiative heat loss. These collectors are used morefrequently for U.S. commercial applications.
There are two types of active solar water heating systems:
Direct circulation systems
Pumps circulatehousehold waterthroughthe collectors and intothe home. They work well in climates where it rarely freezes.
Indirect circulation systems
Pumps circulatea non-freezing,heat-transfer fluid through thecollectors and aheat exchanger.This heats the water that then flows into the home. They are popular inclimates prone to freezing temperatures.