NON-CONVENTIONAL ENERGY RESOURCES AND UTILISATION 71There are eight possible pathways for conversion of solar radiation to useful energy. Solar ther-
mal conversion method converts radiation to heat using solar flat collectors. Solar thermo chemical
conversion method converts radiation to heat and produce steam then to kinetic energy using a pump or
turbine. Solar thermal electric conversion method converts radiation to steam and to kinetic and electri-
cal energy through a turbine and generator to electrical energy. The above route through a further
electrolysis process gives chemical energy (H 2 fuel). A high temperature catalytic conversion process
produces chemical energy (H 2 fuel) directly. Photovoltaic conversion of solar radiation gives direct
electrical energy. Photosynthesis process produces chemical energy directly from radiation. Chemical
energy (H 2 fuel) is directly produced from solar radiation using the electricity produced by the photo-
voltaic method. A few of these methods are dealt in detail further.
Commercial and industrial buildings may use the same solar technologies photovoltaic, passive
heating, day lighting, and water heating that are used for residential buildings. These nonresidential
buildings can also use solar energy technologies that would be impractical for a home. These technolo-
gies include ventilation air preheating, solar process heating and solar cooling.
Many large buildings need ventilated air to maintain indoor air quality. In cold climates, heating
this air can use large amounts of energy. A solar ventilation system can preheat the air, saving both
energy and money. This type of system typically uses a transpired collector, which consists of a thin,
black metal panel mounted on a south-facing wall to absorb the sun’s heat. Air passes through the many
small holes in the panel. A space behind the perforated wall allows the air streams from the holes to mix
together. The heated air is then sucked out from the top of the space into the ventilation system.
Solar process heating systems are designed to provide large quantities of hot water or space
heating for nonresidential buildings. A typical system includes solar collectors that work along with a
pump, a heat exchanger, and/or one or more large storage tanks. The two main types of solar collectors
used an evacuated tube collector and a parabolic trough collector can operate at high temperatures with
high efficiency. An evacuated-tube collector is a shallow box full of many glass, double-walled tubes
and reflectors to heat the fluid inside the tubes. A vacuum between the two walls insulates the inner
tube, holding in the heat. Parabolic troughs are long, rectangular, curved (U-shaped) mirrors tilted to
focus sunlight on a tube, which runs down the center of the trough. This heats the fluid within the tube.
The heat from a solar collector can also be used to cool a building. It may seem impossible to
use heat to cool a building, but it makes more sense if you just think of the solar heat as an energy
source. Your familiar home air conditioner uses an energy source, electricity, to create cool air. Solar
absorption coolers use a similar approach, combined with some very complex chemistry tricks, to
create cool air from solar energy. Solar energy can also be used with evaporative coolers (also called
“swamp coolers”) to extend their usefulness to more humid climates, using another chemistry trick
called desiccant cooling.
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 build-
ings 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.