Efficiency of Solar Panels
Solar power would be the leading source of energy if it were able
to efficiently extract a majority of the energy delivered to the
earth from the sun on a daily basis. On the equator at noon, 1000
watts/m2 of sun energy touches the ground. Unfortunately only about
20 percent of this power can be transferred into usable energy. This
inefficiency is directly related to the percentage of photons that
are absorbed. The electrons in the semiconductor material will only
jump into the conduction band if they absorb a photon. The photons
can either be absorbed, reflected, or can even pass right through
the semiconductor.3 In order to increase the number of photons
absorbed ultimately increasing the efficiency of the solar panel,
the percentage of photons that pass through and reflected must be
reduced. There is an obvious loss of electric potential when the
photons are reflected off the semiconductor material. To reduce the
percentage of reflected photons, an anti-reflective coating is
usually put on the semiconductor, which will decrease the number of
reflected photons increasing the total number of photons that will
become absorbed. However, there is still a chance that these photons
could pass right through the material without striking an electron.
Some of the photons from light pass straight through the
semiconductor as if the semiconductor were transparent. The photons
in sunlight have a wide variety of different wavelengths causing
some to pass right through.4 The photons that pass through the
semiconductor have energy lower than the band gap energy of the
semiconductor.5 As a result, these photons do not contain enough
energy to create an electron-hole pair, so the photon just passes
right through the semiconductor.6 If the photon has more energy than
the band gap of the semiconductor, then the electrons absorb the
photon. However, if the photon has an excess of energy, meaning it
gives the electron more energy than the band gap, than this excess
will be emitted as a form heat and the electron will settle down in
the conduction band. To minimize the amount of photons that pass
through the semiconductor, some semiconductors are manufactured with
many layers, each having a different band gaps in order to better
match the light spectrum. A highly efficient solar panel can be
designed by cascading semiconductor materials with different band
gaps to perfectly match the light spectrum. However, this would
require an infinite amount of semiconductor material making it
utterly impossible. For the solar panels to be cost-effective, the
can only be designed with a few different layers. As a result, there
are still some photons that pass right through the semiconductor and
the energy lost from the absorbed photons as a form of heat.
Solar power is an amazing technology in the sense that it converts
sunlight into electricity through the semiconductor material alone.
However, it is clear that there are many flaws and complications in
the ability to design a solar panel that can utilize a majority of
the energy that is emitted from the sun on a daily basis. There are
numerous ways to design and manufacture solar panels. The uses of
different kinds of semiconductor materials, crystal structures, and
manufacturing methods all have a different affect on the efficiency
and cost of the solar panel. One crystal structure may be more
efficient, but the cost may make it too expensive to consider. As
time goes on, newer manufacturing techniques and designs will prove
these solar panels more efficient and less costly in future years.
Rather than focusing on the issues relating to the design and
semiconductor physics behind the solar panels themselves, this
project will focuses more on the devices that control the output of
the solar panels. A solar panel’s output varies depending on certain
ambient weather conditions such as temperature, illumination, how
clear the sky is, so on and so forth. Our task at hand is to design
a device that will extract the maximum amount of power from the
solar panels, regardless of how efficient or inefficient the solar
panels may be.