Solar Water Heaters
Solar Water Heaters
Solar water heaters—also called solar domestic hot water
systems—can be a cost-effective way to generate hot water for your
home. They can be used in any climate, and the fuel they
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 inlet connected to
and from the collector. In two-tank systems, the solar water heater
preheats water before it enters the conventional water heater. In
one-tank systems, the back-up heater is combined with the solar
storage in one tank.
Three types of solar collectors are used for residential
applications:
-
Flat-plate collector
Glazed flat-plate collectors are insulated, weatherproofed
boxes that contain a dark 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 metal or polymer, without a cover or
enclosure.
-
Integral collector-storage systems
Also known as ICS or batch systems, they feature one
or more black tanks or tubes in an insulated, glazed box. Cold
water first passes through the solar collector, which preheats
the water. The water then continues on to the conventional
backup water heater, providing a reliable source 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 glass tubes. Each
tube contains a glass outer tube and metal absorber tube
attached to a fin. The fin's coating absorbs solar energy but
inhibits radiative heat loss. These collectors are used more
frequently for U.S. commercial applications.
There are two types of active solar water heating systems:
-
Direct circulation systems
Pumps circulate household water through the collectors and
into the home. They work well in climates where it rarely
freezes.
-
Indirect circulation systems
Pumps circulate a non-freezing, heat-transfer fluid through
the collectors and a heat exchanger. This heats the water that
then flows into the home. They are popular in climates prone to
freezing temperatures.
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