Solar thermal energy
Practical Action
For passive solar design to be effective certain guidelines should be followed:
a building should have large areas of glazing facing the sun to maximise solar gain
features should be included to regulate heat intake to prevent the building from
overheating
a building should be of sufficient mass to allow heat storage for the required period
contain features which promote the even distribution of heat throughout the building
One example of a simple passive space heating technology is the Trombe wall. A massive black
painted wall has a double glazed skin to prevent captured heat from escaping. The wall is
vented to allow the warm air to enter the room at high level and cool air to enter the cavity
between the wall and the glazing. Heat stored during the wall during the day is radiated into the
room during the night. This type of technology is useful in areas where the nights are cold but
the days are warm and sunny.
Greenhouses
It is possible to expand the diversity of crops grown in mountain areas and therefore enhance
the nutritional balance of family diets by the use of simple greenhouse structures. However,
the low-cost materials such as polythene sheets and wooden pole frames are vulnerable to
damage in the harsh climate of mountainous regions.
Seawater Greenhouse
A solar energy application in which evaporative cooling and desalination are combined to
produce an enhanced environment for crops to grow in hot arid regions and provide clean
water.
Seawater is fed onto porous cardboard evaporators and humidified air is drawn into the
greenhouse. This provides a cooling effect that reduces the temperature within the
greenhouse. At the other end of the greenhouse a plastic condenser captures the clean water
from the air. The condenser uses cold seawater as a coolant.
The greenhouse is made of a light steel structure with a polythene covering. The polythene
films are treated to incorporate ultraviolet-reflecting and infrared-absorbing properties. The
cardboard evaporators become strengthened by the crystallise calcium carbonate from the
sea water.
http://www.seawatergreenhouse.com/
Less common applications
Solar-thermodyamic water pumping
Many solar water pumping systems are based on photovoltaic technology combined with a
battery storage system and an electric pump. Solar thermodynamic systems use the heat from
the sun to power a pump.
The system can be divided into the following components
The solar collector which converts radiation to heat
The heat engine which uses a thermodynamic cycle to convert heat into mechanical
energy
The pump
The water storage and distribution system
To convert the thermal energy to mechanical pumping a heat engine is used which can be
based on a Ranking cycle or a Stirling cycle. These engines operate through the use of
external heat sources including solar energy but any heat source can be used. In addition to
driving a water pump these heat engines can also be used in other applications and can
generate electricity when combined with a generator.
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