Using the sun to heat water can be cost-effective and
environmentally friendly. Solar water heating is generally more sensible for
families that use a lot of hot water. Although it can work anywhere, it is
more cost-effective at lower latitudes and in sunnier climates.
A solar water heater needs a backup system. One easy way to
provide backup is to add a solar system to an electric or gas storage water
heater. A tankless heater can also be used for backup.
There are active and passive solar water heaters. The
simplest systems are passive, using nothing but solar energy and gravity to
circulate water between the storage tank and the collector, where the water
heats up. As water in the collector heats, the hotter water rises into a
storage tank placed slightly above the collector, while cooler water runs down
to replace it. Active systems are generally more reliable than passive ones,
and they can be put in more places. They usually have a pump to move the water
from the collector to the storage tank, so the collector can be on the roof,
in the yard, or wherever is convenient.
Solar hot water systems can be vulnerable to freezing. If
outdoor water lines freeze, their piping can be destroyed. Open-loop systems,
which run tap water through the system, need to be protected. But no matter
how well protected they are, temperatures below 35°F will keep these systems
from functioning. A closed loop, which runs antifreeze or air through the
outdoor pipes and then transfers the heat to the tap water, will keep the
pipes from freezing.
Open-loop solar systems circulate tap water directly
through the collector and store it in the tank. This works best with water
that is not hard or acidic. Hard or acidic water corrodes the copper pipes of
the collector, causes scale deposition, lowers efficiency and reduces life
span of the system.
Closed-loop systems circulate heat transfer fluid, instead
of tap water, through the collector. This fluid may be treated water, air,
antifreeze solution, or a special oil. It picks up heat in the collector and
transfers it to water. These systems are easier to install, but more expensive
to operate and maintain.
Especially in open loop systems the points to check are :
-
Does the collector have a suitable, well protected body?
Fibreglass body is preferable but well treated Mild Steel (7 tank
treated/epoxy painted) or aluminum section/sheet (with suitable treatment)
will work just as well.
-
Does the absorber assembly have all copper assembly (
header-riser-copper absorber)?
-
Does the absorber assembly have 9 risers?
Careful assessment of the present and future requirement of hot water for
bathing, cooking, cleaning, washing, etc. for the entire family/unit,
selection of the system capacity and proper installation and thereafter proper
usage will ensure that entire hot water requirements around the year can be
practically met by the solar water heating system.
Rule of thumb : each person uses about 20 litres per day hot water under
normal circumstances, for bathing. Hence for a family of 4 a system of 100 lpd/60
deg. c. is sufficient. If tub bath is taken then the requirement rises to 50
litres per person. If hot water is used for washing, cooking and cleaning
then system dimensioning must be taken into consideration accordingly.
Provision should also be made for unexpected guests!
