Curriculum to convert light to electricity.
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We know that silicon is a semiconductor material. For that
reasons it causes electrons flow, creating electricity. Solar power generating
systems take advantage of this property to convert sunlight directly into
electrical energy.
There are two types of solar power generating systems:
grid-connected systems, which are connected to the commercial power
infrastructure; and stand-alone systems, which feed electricity to a facility
for immediate use, or to a battery for storage.
Sunlight is composed of miniscule particles called photons,
which radiate from the sun. As these hit the silicon atoms of the solar cell,
they transfer their energy to lose electrons, knocking them clean off the
atoms. The photons could be compared to the white ball in a game of pool, which
passes on its energy to the coloured balls it strikes.
Freeing up electrons is however only half the work of a
solar cell: it then needs to herd these stray electrons into an electric
current. This involves creating an electrical imbalance within the cell, which
acts a bit like a slope down which the electrons will flow in the same
direction.
Creating this imbalance is made possible by the internal
organisation of silicon. Silicon atoms are arranged together in a tightly bound
structure. By squeezing small quantities of other elements into this structure,
two different types of silicon are created: n-type, which has spare electrons,
and p-type, which is missing electrons, leaving ‘holes’ in their place.
When these two materials are placed side by side inside a
solar cell, the n-type silicon’s spare electrons jump over to fill the gaps in
the p-type silicon. This means that the n-type silicon becomes positively
charged, and the p-type silicon is negatively charged, creating an electric
field across the cell. Because silicon is a semi-conductor, it can act like an
insulator, maintaining this imbalance.
As the photons smash the electrons off the silicon atoms,
this field drives them along in an orderly manner, providing the electric
current to power calculators, satellites and everything in between.
Grid-connected systems are used for homes, public facilities
such as schools and hospitals, and commercial facilities such as offices and
shopping centres. Electricity generated during the daytime can be used right away,
and in some cases surplus electricity can be sold to the utility power company.
If the system doesn’t generate enough electricity, or generates none at all
(for example, on a cloudy or rainy day, or at night) electricity is purchased
from the utility power company. Power production levels and surplus selling can
be checked in real time on a monitor, an effective way to gauge daily energy
consumption.
Stand-alone systems are used in a variety of applications,
including emergency power supply and remote power where traditional
infrastructure is unavailable.
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