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INTRODUCTION In
the present situation energy crisis is an important unsolvable problem so we must
find out some other ways to trust all sources such as solar energy, hydro power,
tidal power, wind power etc. Using solar power to produce electricity is not the
same as using solar to produce heat. Solar thermal principles are applied to produce
hot fluids or air. Photovoltaic principles are used to produce electricity. A
solar panel (PV panel) is made of the natural element, silicon, which becomes
charged electrically when subjected to sun light.
Solar panels are directed at solar south in the northern hemisphere and solar
north in the southern hemisphere (these are slightly different than magnetic compass
north-south directions) at an angle dictated by the geographic location and latitude
of where they are to be installed. Typically, the angle of the solar array is
set within a range of between site-latitude-plus 15 degrees and site-latitude-minus
15 degrees, depending on whether a slight winter or summer bias is desirable in
the system. Many solar arrays are placed at an angle equal to the site latitude
with no bias for seasonal periods.
This electrical charge is consolidated in the PV panel and directed to the output
terminals to produce low voltage (Direct Current) - usually 6 to 24 volts. The
most common output is intended for nominal 12 volts, with an effective output
usually up to 17 volts. A 12 volt nominal output is the reference voltage, but
the operating voltage can be 17 volts or higher much like your car alternator
charges your 12 volt battery at well over 12 volts. So there's a difference between
the reference voltage and the actual operating voltage.
BASIC
PRINCIPLES
When Light Hits the Cell
When light, in the form of photons, hits our solar cell, its energy frees electron-hole
pairs. Each photon with enough energy will normally free exactly one electron,
and result in a free hole as well. If this happens close enough to the electric
field, or if free electron and free hole happen to wander into its range of influence,
the field will send the electron to the N side and the hole to the P side. This
causes further disruption of electrical neutrality, and if we provide an external
current path, electrons will flow through the path to their original side (the
P side) to unite with holes that the electric field sent there, doing work for
us along the way. The electron flow provides the current, and the cell's electric
field causes a voltage. With both current and voltage, we have power, which is
the product of the two.
Operation of a PV cell
Silicon in Solar Cells
A solar cell has silicon with impurities -- other atoms mixed in with the silicon
atoms, changing the way things work a bit. We usually think of impurities as something
undesirable, but in our case, our cell wouldn't work without them. These impurities
are actually put there on purpose. Consider silicon with an atom of phosphorous
here and there, maybe one for every million silicon atoms. Phosphorous has five
electrons in its outer shell, not four. It still bonds with its silicon neighbor
atoms, but in a sense, the phosphorous has one electron that doesn't have anyone
to hold hands with. It doesn't form part of a bond, but there is a positive proton
in the phosphorous nucleus holding it in place.
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