Solar thermal energy
Practical Action
Open loop systems allow water to run through the solar panels and be stored in the
storage tank to be used.
Closed loop systems are where the water that circulates through the solar panel is
separate from the water used. The system uses a heat exchanger. This means that anti
freeze can be added to the water running through the panels which allows them to be
used in cold climates.
Atmospheric systems are used where there is no mains water delivery to the storage
tank so as water is taken from the hot water tank it is replaced from an additional cold
water tank that is located above it. A break pressure valves allows water to feed the hot
water tank when required. Atmospheric systems can be open loop or closed loop.
Batch solar water heating systems are used as a simple approach to obtaining hot
water. The system is filled with water and left to heat up. Once the water is heated up it
can be used as required but system has to be refilled manually.
Simple Solar Water Heater for Developing Countries
A. Jagadeesh, Homepower Issue 76 http://www.homepower.com/
More than 90% of systems worldwide are based on the thermosyphon principle.
Pumped solar water heaters use a pumping device to drive the water through the
collector. The advantage of this system is that the storage tank can be sited below the
collector. The disadvantage of course is that electricity is required to drive the pump.
Often the fluid circulating in the collector will be treated with an anti-corrosive and /or
anti-freeze chemical. In this case, a heat exchanger is required to transfer the heat to
the consumers hot water supply.
Integrated systems combine the function of tank and collector to reduce cost and size.
Water heating systems can be made relatively simply while more sophisticated systems are
available at a higher price. Evacuated tube collectors have the heat absorbing element placed
within an evacuated glass sheath to minimise heat losses. System complexity also varies
depending on use.
For commercial applications, banks of collectors are used to provide larger quantities of hot
water as required. Many such systems are in use at hospitals in developing countries.
A solar pond is an approach that uses large bodies of water to collect and store solar thermal
energy with relatively little equipment. The pond uses the principle that slat water is heavier
than fresh water so a layer of salt water at the bottom of the pond traps the heat energy and
the temperature can rise above 90°C.
Solar ponds can be used to provide heating to houses but can also be used for other
applications. For example, using a low temperature turbine the solar pond can be used to
generate electricity or it can be used to provide power to a water distillation unit as developed
by The University of Texas.
Bhuj, Gujarat has the largest operating solar pond in India covering an area of 6000 m2
which is used to supply process heat to the Kutch dairy.
The solar pond was developed by the Gujarat Energy Development Agency (GEDA), the Tata
Energy Research Institute (TERI) and the Gujarat Dairy Development Corporation (GDDC).
http://www.teriin.org/tech_solarponds.php
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