What is Solar Water
Heating?
Service Pemanas Air Sun Hot Solar water heating
collectors capture and retain heat from the sun and transfer this heat to a
liquid. Solar thermal heat is trapped using the “greenhouse effect,” in this
case is the ability of a reflective surface to transmit short wave radiation
and reflect long wave radiation. Heat and infrared radiation (IR) are produced
when short wave radiation light hits a collector’s absorber, which is then
trapped inside the collector. Fluid, usually water, in contact with the absorber
collects the trapped heat to transfer it to storage.
Two principles govern
solar thermal collectors. First, any hot object eventually looses its heat back
to the environment. The efficiency of a solar thermal collector is directly
related to heat loss, mainly from convection and radiation. Thermal insulation
is used to slow down heat loss from a hot object to its environment.
Second, heat loss is
more rapid if the temperature difference between a hot object and its
environment is larger, in this case between the temperature of the collector
surface and the ambient temperature. (But the same goes for transferring heat
from the collector to the fluid, a larger difference between the collector and
the liquid, the more heat is transferred.)
The most basic
approach to solar heating of water is to simply put a tank filled with water
into the sun. The heat from the sun would heat the metal tank and the water
inside. This was how the very first SWH systems worked more than a century ago.
However, this setup would be inefficient because there is little to limit the
heat loss from the tank. Adding an insulated box around the tank, and adding
glass above the top where the sun comes in would do a lot to retain heat.
A more common
collector is called a flat plate collector. It has a large, flat surface area
(absorber) to maximize exposure to the sun, and has small tubes bonded to it.
Fluid runs through the tubes, collecting the heat from the absorber. The sides
and bottom of the collector are well-insulated, and glass on top completes the
insulation.
This is quite simple,
but there are some very technical factors involved in making the collector as
efficient as possible. One is the coating on the absorber, which is specially
formulated to both absorb as much heat as possible, and to radiate back out as
little heat as possible. Another is the glass, which is high-iron and specially
coated to let as much light energy as possible through and to also prevent as
much heat loss as possible.
Another popular type
of collector is called evacuated tube, which has a long, skinny absorber that
is inside a glass tube. The tube has the air evacuated out of it, which makes
it highly insulated—not too different from a thermos used to keep drinks hot.
The final type of
collector is a parabolic dish or tray, which increases heat potential by
concentrating sunlight onto a small absorber. These are very rare in home water
heating systems, and more commonly used in utility-scale systems to create
steam which runs turbines to make electricity.
The basic components
in home solar heating systems include:
·
Collectors to take the
heat from the sun and pass it to a fluid
·
The heat transfer
fluid which takes the heat from the collector for use or storage
·
Heat exchangers to
transfer the heat from the fluid to a home’s domestic water.
·
Pumps to move the
fluid through the collector and/or the exchanger, and sometimes to move the
domestic water through the other side of the exchanger.
·
Controllers to run the
pumps when there is collector heat available.
