Solar thermal energy
Practical Action
evaporates which then condenses on the underside of the covering glass. The glass is at an
angle so the water drains off and is captured in a trough separate to the contaminated water.
Solar distillation can be combined with other useful functions so that a solar still may also be
used for rainwater harvesting if modified slightly.
Solar pasteurisation
In pasteurization, water is heated to 149°F (65°C) for about six minutes, killing all the
germs, viruses, and parasites that cause disease in humans, including cholera and hepatitis A
and B. This is similar to what is done with milk and other beverages. It is not necessary to
boil the water as many people believe. Pasteurization is not the only way to decontaminate
drinking water, but it is particularly easy to scale down so that the initial cost is low.
The Solar Puddle - A New Water Pasteurization Technique Boiling Point No. 36 - November
1995, GTZ, Practical Action.
Refrigeration / cooling
Preservation of crops and food can be improved with relatively simple evaporative cooling
techniques. This approach keep produce fresh by using the evaporation of water to reduce the
temperature minimise the impact of the suns energy. Evaporative cooling works best in dry
climates and the greater the amount of humidity in the air the less effective it is at reducing the
temperature. A similar approach has been use to keep building cool by placing a ceramic pot
containing waster in window and allowing the air to pass over the pot as it enters the building.
This results in a cooler wetter environment in the room.
Solar thermal energy in architecture
There are two basic requirements within buildings – heating and cooling. Many technological
advances have been made in design of ‘solar buildings’ for solar heating in developed countries
but the technology is often expensive and out of reach for rural communities in developing
countries.
Space cooling
The majority of the world’s developing countries, however, lie within the tropics and do not need
space heating but there is a demand for space cooling. There are many traditional, simple,
elegant techniques for cooling their dwellings, often using effects promoted by passive solar
phenomenon.
There are many methods for minimising heat gain. These include siting a building in shade or
near water, using vegetation or landscaping to direct wind into the building, good town planning
to optimise the prevailing wind and available shade. Buildings can be designed for a given
climate - domed roofs and thermally massive structures in hot arid climates, shuttered and
shaded windows to prevent heat gain, open structure bamboo housing in warm, humid areas. In
some countries dwellings are constructed underground and take advantage of the relatively low
and stable temperature of the surrounding ground. There are as many options as there are
people.
Space heating
In colder areas of the world (including high altitude areas within the tropics) space heating is
often required during the winter months. Vast quantities of energy can be used to achieve this.
If buildings are carefully designed to take full advantage of the solar insolation which they
receive then much of the heating requirement can be met by solar gain alone. By incorporating
certain simple design principles a new dwelling can be made to be fuel efficient and
comfortable for habitation. The bulk of these technologies are architecture based and passive
in nature. The use of building materials with a high thermal mass (which stores heat), good
insulation and large glazed areas can increase a buildings capacity to capture and store heat
from the sun. Many technologies exist to assist with diurnal heating needs but seasonal storage
is more difficult and costly.
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