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| A
typical flat-plate collector is a metal
box with a glass or plastic cover (called
glazing) on top and a dark-colored
absorber plate on the bottom. The sides
and bottom of the collector are usually
insulated to minimize heat loss. |
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Sunlight passes
through the glazing and strikes the absorber
plate, which heats up, changing solar energy into
heat energy. The heat is transferred to liquid
passing through pipes attached to the absorber
plate. Absorber plates are commonly painted with
"selective coatings," which absorb and
retain heat better than ordinary black paint.
Absorber plates are usually made of
metal—typically copper or aluminum—because the
metal is a good heat conductor. Copper is more
expensive, but is a better conductor and less
prone to corrosion than aluminum. In locations
with average available solar energy, flat plate
collectors are sized approximately one-half- to
one-square foot per gallon of one-day's hot water
use. |
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| Applications: The
main use of this technology is in residential
buildings where the demand for hot water has a
large impact on energy bills. This generally means
a situation with a large family, or a situation in
which the hot water demand is excessive due to
frequent laundry washing.
Commercial
applications include laundromats, car washes,
military laundry facilities and eating
establishments. The technology can also be used
for space heating if the building is located
off-grid or if utility power is subject to
frequent outages. Solar water heating systems are
most likely to be cost effective for facilities
with water heating systems that are expensive to
operate, or with operations such as laundries or
kitchens that require large quantities of hot
water.
unglazed liquid
collectors are commonly used to heat water for
swimming pools. Because these collectors need not
withstand high temperatures, they can use less
expensive materials such as plastic or rubber.
They also do not require freeze-proofing because
swimming pools are generally used only in warm
weather or can be drained easily during cold
weather.
While solar
collectors are most cost-effective in sunny,
temperate areas, they can be cost effective
virtually anywhere in the country so should be
considered. |
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| Performance/Costs: To
compare performance ratings, look for a Solar
Rating & Certification Corporation (SRCC) or
Florida Solar Energy Center (FSEC) sticker on the
equipment you are considering. Paybacks - (The
amount of time required - usually in years - for
positive cash flows to equal the total investment
costs. This is often used to describe how long it
will take for energy savings resulting from using
more energy-efficient equipment to equal the
premium paid to purchase the more energy-efficient
equipment.)
- vary widely, but for a well-designed and
properly installed solar water heater, you can
expect a simple payback of 4 to 10 years,
depending on climate and utility costs. FSEC found
that solar water heaters offer potential savings,
compared to electric water heating, of as much as
50% to 85% in the water heating portion of the
utility bill.
Flat plate water
heating systems range in price from about $2,000
to $4,000 installed for residential systems (for
40 to 80 gallons per day usage), and $2,000 to
$50,000 for commercial systems (for 40 to 1700
gallons per day usage). The following chart
compares the percent of water heating energy that
solar can provide in various cities for a
48-square-foot flat plate solar hot water system
based on average water usage for four persons. |
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