Active solar heating system is mainly used for domestic hot water heating in colder regions, where sun's heat energy is collected inside the solar collectors and transferred through the heat exchanger to heat the water stored inside the storage tank.
All active solar water heaters
use a pump to circulate the solar thermal fluid through the system,
sensors to protect and other controls which will
efficiency and better performance versus the passive systems.
solar heating is applicable in colder regions, but to eliminate the
risk of freezing you have to use the antifreeze as the thermal
fluid. As the required heat or temperature is usually not met with the
system, backup heating has to be provided (electrical heating
elements for example).
The efficiency of an
active solar water heater and its performance depends on the system
design, quality of material used, how well the system is installed and
maintained and the amount of time the system is exposed to the sun.
Active solar energy system for water heating can use controllers with sensors to control the pump or Photovoltaic solar collector where the pump runs only when sun heat energy is available.
Active solar heating systems are using liquid-to-water and air-to-water heat transfer to heat the water. Two active water heating systems are the most popular:
The above examples of active solar water heating systems can use Photovoltaic panels to run the pump and operate as:
Direct or in the open-loop systems
Indirect or in the closed-loop systems
Direct active solar energy systems utilize solar
where household water is heated directly, which is the reason for being
more efficient than indirect systems.
On the other side the main disadvantage is that they require more maintenance due to the mineral buildup problem. In a case of the solar panels which are built from the small size tubes, scaling might clog the pipe, reduce the water flow and decrease the collector efficiency.
Indirect active solar water heater systems
are closed-loop systems where the solar fluid remains within a
circuit. Solar thermal fluid, glycol for example, after it is
heated in the collector by the sun is moved by the pump to the
exchanger where it transfers the heat to domestic water.
systems mainly use popular solar panels or flat plate collectors,
and also evacuated tubes
and concentrated collectors.
A good example of the closed loop glycol design is the Rheem Solpak active solar system.
simplest active solar water heating
system is the open-loop system, often seen in the warmer regions, where
freezing never occurs. The main components are solar collector, pump,
controllers, sensors (i.e. temperature limit) and valves (i.e.
tempering valve, isolation valves, air vent).
In the open-loop systems, solar collector is attached through the pipeline to the storage tank. Once the water is heated inside the collectors, the pump circulates the heated water and when it stops, the circulation stops as well.
The most popular and used collectors for this active system are solar panels or flat-plate collectors and vacuum tubes.
Antifreeze pressurized system
is an example of the closed-loop active solar heating systems, where
water inside the storage tank is heated by the fluid that absorbs
the sun's heat inside the solar collectors and runs through
the heat exchanger.
The heating fluid is usually a 50/50 propylene-glycol and
works as the antifreeze. Double walled heat exchanger must be used if
the heat transfer fluid is considered toxic and single walled if the
fluid is non-toxic.
to its ability to work in a lower temperature environment, closed-loop
with antifreeze active solar heating is the only reliable solution in
Pressurized glycol systems are the most versatile systems of all solar water heating systems. They can be installed in any direction and far from the heat exchanger. Fill and drain valves must be installed as the system is pressurized in order to add or change the fluid.
is another example of the closed loop systems where the circulating
fluid is distilled water. The main advantage of the drainback system
is its ability to empty the solar collector when the pump is turned
off. Drainback active solar water heating systems can be installed in
colder and warmer areas.
The main components of the drainback
system are the collector, pump, large storage tank (size
on the demand, i.e. 80 gallons), small drainback tank (for example
10-gallon), sensors, controllers and valves.
In warmer areas
when the storage tank gets really hot (but not above the maximum as it
is controlled by the temperature limit sensor), the solar fluid drains
out of the collectors preventing the system failure.
colder areas drainback active systems are subjected to freeze-ups
put the antifreeze solution and remove all water from the collectors
piping, when the system is not collecting the sun's heat. Provide
continuous slope of the solar panel and that will keep the pipes and
collector from freezing.
Distilled water is used to transfer heat
from solar collector to domestic water, and it is stored
in the drainback reservoir. Distilled water is used due to its
capability to increase heat transfer and
To allow complete drainage a slight tilt of the
collectors is required. This is why the collector has to be
installed higher than the storage tank. Flat-plate panels are
most popular choices, but they can also use
active heating systems are reliable and long lasting. If this active
system is designed properly (i.e. collector and the pump size) there
won't be any problem, and it will work perfect for a long
time and in any climate. Drainback kits are also available for DIY
Note: Adding antifreeze to the drainback system can decrease the efficiency of solar collectors. When the system is drained, thin film of the antifreeze stays on the tube walls, dries and leaves the small deposits which can build-up over time affecting the water flow and heat transfer. If only distilled water is used the fluid rarely needs to be changed.
(PV) operated active solar heating is using the pump only when the sun
is shining. The pump is DC (direct current) and is operated by the PV
panel that converts the sunlight into direct current electricity. The
PV power can be used for both direct and indirect systems. PV systems
reliable and efficient, providing hot water when other systems
shut down by the power outages.
Which one of the above active solar heating systems is right
It depends on the location. Other important factors
quality of materials used for collectors, strength, reliability... is
the system properly installed and oriented.
The above active systems allow greater flexibility than the passive systems as the solar storage water tank doesn't have to be above or even close to the collectors. They can be used year round which is not the case with passive. Even with higher initial cost expect the payback in 5-10 years.
(Pictures are courtesy of zenrenewables.com and wikipedia.org)