Hot water is required for many purposes and the sun can be used effectively, efficiently and
economically to provide this heat. The warming effect of solar radiation is obvious and it is
well known that a container of cold water, left exposed to the sun will be raised in
temperature. Solar water heating systems are designed to make convenient use of this
Solar water heaters generally employ a solar collector and a storage tank. The collector is by
far the most widespread solar energy conversion device and there are several million in use
around the world, of which designs vary from very simple to complex. The extent to which
construction and manufacture is easily achievable varies around the world but there are some
encouraging examples of innovations and government schemes which have greatly increased
the application of solar water heating, not only in affluent areas but also in poorer, less
developed and often rural areas.
The availability of solar energy
Please refer to the technical brief “Solar Thermal Energy” for details on the availability and
varaiation of solar energy around the world. Insert link here….?
Passive vs. Active
Solar thermal systems in their simplest form consist of a solar collector and a storage tank.
These systems are termed passive, whilst those that contain circulating pumps are known as
active systems. (Solar Water Heater Industry in China, 2010)
Passive systems rely on the natural buoyancy or thermosyphon effect created when the
temperature of the water in the collector rises, causing the water itself to rise as it becomes
less dense with increased temperature, thus inducing circulation in the circuit.
No electricity required for operation
Minimal running costs
Maintenance costs reduced as no
Reduced flexibility as collector has to
be located beneath the solar store
Less reliable as inconsistent rate of
Table 1: Advantages and Disadvantages of Passive Solar Water Heating Systems
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