Benefits of Solar Water
Heaters
by staff writer
Increasing interest in solar water heating systems is being driven by rising
energy prices. The initial costs are higher than traditional gas or electric
water heaters, but solar water heaters can operate more efficiently and can save
money in the long run. In many cases, a traditional water heater is still
installed as a backup. This setup still delivers savings since water entering
the traditional water heater is preheated. The amount of hot water a solar water
heater produces depends on the type of system, collector area, and potential
solar energy. Choosing the right system is critical to achieve peak energy
efficiency.
 All solar water heaters utilize collectors to capture solar energy as heat. Flat
plate collectors are well-insulated boxes containing a black adsorber plate
shielded by several layers of glass or other transparent material. Light travels
through the glass and strikes the adsorber plate, turning the light's energy
into heat. Fluid is circulated through tubing attached to the back plate to
collect and transfer the heat to where it is needed. Evacuated tube collectors
have two lines running through the inner tube, which is the adsorber. A vacuum
between the inner tube and the outer tube minimizes heat loss. Evacuated tube
collectors have the ability to effectively collect heat in cooler climates and
during cloudy days. Unsurprisingly, evacuated tube collectors are more expensive
than flat plate collectors.
 After fluid has been heated in the collector, it flows to an insulated storage
tank -- where it is ready for use -- or to a heat exchanger. Some solar water
heaters have a storage tank attached to the collector, but most often they are
independent units. A storage tank may not be required for some applications,
like heating a swimming pool, but it is a very common component in most
installations.
Solar water heaters are either active or passive. Active systems use electric
pumps, valves, and controllers to move fluid through the system. Active solar
water heater systems have the potential to be more efficient, but they tend to
cost more, need more maintenance, and require electricity. When retrofitting a
home, active design is usually selected because it offers
greater flexibility
regarding the location of the solar collectors and storage tank. Passive systems
have no pump or electrical requirements. They are not as efficient, but they
cost less, require less maintenance, and are more reliable.
Systems are also classified as direct (open loop) or indirect (closed loop).
Direct systems use solar energy to directly heat the water you will drink,
shower with, etc. Indirect systems separate the fluid that circulates through
the solar collectors from the water that you will consume. The primary
difference in equipment is whether a heat exchanger is used to warm the potable
water. Indirect systems are almost always active due to the increased
circulation requirements. Climate and the potential for freezing temperatures
are major considerations when choosing between direct and indirect systems.
Indirect solar water heaters may use water in the solar collector loop, but it
is also possible to use a combination of water and glycol. The combination of
water and glycol is a very typical antifreeze mix which has a lower freezing
point than water (as low as -60°F). Glycol is toxic, so heat exchangers are
typically double-walled for safety. Indirect systems are more expensive and
require more maintenance, but they offer the benefit of operating in areas that
experience freezing temperatures.
Many people don't realize that solar water heaters can function in almost any
climate. Their effectiveness depends on available solar energy, but also
on the
temperature of the water source. If a solar water heater can increase the
temperature of incoming water from 60°F to 90°F, this can provide a
substantial
energy saving when used in conjunction with a traditional water heater. That’s
30°F that you don't have to heat with gas or electricity!
Careful research is required to size your solar water heating system
appropriately. Consider your family's
average water usage, local climate and the
potential for freezing weather, and the efficiency of the system
you are
interested in. It is also advisable to make sure there are no restrictions in
the local building codes or neighborhood covenants before installing a solar
water heater.
With proper planning, installing a solar water heater can protect you from
rising energy costs, reduce your carbon footprint, and make your homestead a
little more self-sufficient. |
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