Solar Hot Water Systems Components
Most solar water-heating system have three main parts: (1) a
solar collector and (2) a solar storage tank or a pool/tub (3)
Plumbing and Solar Control System. Until recently the most
common collector used in solar hot water systems was the flat
panel collector. However with the advance in technology, solar
vacuum tube technology is rapidly becoming the method of
choice as its energy output is much higher and takes up less
space per square foot. Mass production of solar tubes has driven
the cost down to allow widespread use of vacuum tubes.
Solar water heaters use the sun to heat either water or a heat-transfer fluid in the collector. Heated water is
then held in the storage tank ready for use or directly circulated in an open mass such as pool or hot tub.
The tank can be as simple as a modified standard water heater, but more specific solar water tanks are
also available. Most solar water tanks will also feature a back up electric element built into the unit.
One of the most overlooked aspect of a solar system is the Plumbing and Control System. This includes
all items required to make the system function optimally and safely. Items such as temperature
controllers, pumps, expansion vessels, pressure safety valves, fill and drain spouts are all part of a
properly installed solar system.
ACTIVE or PASSIVE System
Solar water heating systems can be either active or passive, but the most common are active systems.
Northern Lights Solar Solutions designs application based around active system with pumps and and
digital controllers designed specifically for the solar industry.
Active Direct-circulation (open loop
systems) use pumps to circulate potable water
through the collectors. These systems are
appropriate in areas that do not freeze for long
periods and do not have hard or acidic water.
These systems may require a recirculation
freeze protection (circulating warm tank
water during freeze conditions) and this in
return requires electrical power for the
protection to be effective. An open loop
system operates at atmospheric pressure. A
pool uses this method as it is generally not
operated in freezing months. In an open loop
system the usable hot water is directly
circulated through the heating system.
Active Indirect-circulation (closed loop) uses a
heat-transfer fluid (water or a diluted antifreeze
fluid) to collect heat and a heat exchanger to
transfer the heat to the potable water indirectly.
Heat exchangers transfer the heat from the heated
fluid to the potable water (or other fluid). Some
indirect systems have "overheat protection" bypass which removes the heat that cannot be used.
This protects the collector and the glycol fluid
from becoming super-heated when the load is low
and the solar intensity of incoming solar radiation
is high. The heat transfer fluid is usually a glycolwater mixture with the glycol concentration
depending on the expected minimum temperature.
The glycol is usually food-grade Propylene glycol
because it is non-toxic. This system is typically
used in hot water heating and radiator or in floor
home/commercial heating. Because the system is
closed to the atmosphere, pressure can build up
as the temperature rises. Such systems will
incorporate pressure relief valves and expansion
tanks for safety purposes
Passive solar water heaters systems move
household water or a heat-transfer fluid
through the system without pumps. They rely
on gravity and the tendency for water to
naturally circulate as it is heated (warm water
is lighter and rises). Because they contain no
electrical components, passive systems
though simpler, have very minimal control for
home use. Passive storage systems consist of
one or more storage tanks placed in an
insulated box with a glazed side facing the
sun. These solar collectors are suited for areas
where temperatures rarely go below freezing.
They are also good in households with
significant daytime and evening hot-water
needs; but they do not work well in
households with predominantly morning
draws because they lose most of the collected
energy overnight.
Common Solar Heating System Applications
In Japan an estimated 10,000,000 homes use this
technology to heat their homes. In North America solar
water heating is quickly growing as the price of solar
collectors fall and governments support the use of clean
energy, financially. A hot water system is in most cases
done using a close loop system with glycol mixture running
through the primary side of a heat exchanger. Special solar
water tanks are now available that have the heat exchanger
built directly inside the system, An existing hot water
system can also be quickly adapted by using a primary
storage hot water tank before the existing secondary tanks.
Using a heat exchanger and solar system would heat the
primary storage tank. Water would then be drawn into the
existing water tank as needed. This is perhaps the most
common type of home water heating as the current system
is left in place and solar water compliments the system.
When installing a hot water system, a controller and pump
are required. There should also be proper pressure release
valves used.