| solar energy
Photovoltaics
Solar
cells convert sunlight directly into electricity. When sunlight is absorbed
by the semi-conducting materials of the solar cells, the electrons absorb the
photons and become liberated from their atoms and flow through the material to
produce electricity. This process of converting light (photons) to electricity
(voltage) is called the photovoltaic (PV) effect.
Other
than the crystalline silicon solar cells, there are also thin film solar cells
that use layers of semiconductor materials only a few micrometers thick.
Thin film technology has made it possible for solar cells to be used in building
materials such as building facades or roof shingles. The
performance of a solar cell is measured in terms of its efficiency at converting
sunlight into electricity. Only light of certain energies will work efficiently
to create electricity, most of it is reflected or absorbed by the material that
make up the solar cell. The loss of energy reduces the cell efficiency to
about 15%. Low efficiencies mean that larger arrays are needed, which equates
to higher cost. Learn more about: TOP Solar
Heating
Most solar water heating
systems for buildings have two main parts: a solar collector and a storage tank.
The most common collector is called a flat-plate collector which is mounted on
the roof. It consists of a thin rectangular box with a transparent cover that
faces the sun to collect the heat. Small tubes run through the box and carry
the liquid (water) to be heated. The tubes are attached to an absorber plate
which is usually painted black to absorb heat. As heat builds up in the
collector, it heats the fluid passing through the tubes. The
insulated storage tank then holds the hot fluid. Solar water heating systems
can be either active or passive. Active systems rely on pumps to move the
liquid between the collector and the storage tank, while passive systems rely
on gravity and the tendency for water to naturally circulate as it is heated (thermosyphon). Learn more about: TOP
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