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Unit 3.1
Minidoc-Solar Power
The mini-documentary deals with the chemistry of
photovoltaics using silicon semiconductors. The advantages
of solar energy are discussed.
Video program cues: 00:30 — 5:05
Trapping solar power
"It’s really a combination of chemistry
and physics: the solar cells are made out of silicon; it’s
a semi conductor, which is very abundant on earth. The photovoltaic
process itself is fairly simple after all. Photons from
the sun hit the silicon. If they have enough energy, they
are going to split one of the silicon atoms into a silicon
ion, Si+ and an electron. If you don’t do anything
with them, they recombine, because everything is at stable
conditions and is neutral, so the charge will be just the
same. If you attach wires on the front and the back, after
creating physical field, a positive/negative field, you
will be able to separate this electron and the silicon positive
ion for enough time to have them go out of the cell, go
into another appliance do some useful work there, and go
back through the back of the cell.
"So, it’s fairly very simple, because
we’re just splitting an atom into an ion and an electron
and the electron goes out into the load [electrical appliance],
comes back through the back [of the solar panel] and then
the circuit is closed and we have enough energy for the
device."
Dr. Jean Posbic
BP Solar, Maryland
Manufacturing solar power
"Phosphorous is a group V element, it
has an extra electron in its last layer, which means that
it is going to share it with the silicon around it. Which
means that it is an n, negatively doped area of the silicon.
Hence, you have a field, a negative to positive field, that
when the photon hits the solar cell, will create a field
to separate the electron from the silicon ion, during this
process".
"So here in this case, this machine
is going to do the printing on the cells. We are printing
on the front and on the back some metals in order to capture
the electricity from the solar cell. The back is completely
covered with silver, because we don’t have any light
coming from the back, and we have a very conductive material,
silicon is very good at that. The front is covered with
very thin fingers, that allow light to come through the
wafer, and create electricity from the sun. The cells that
we saw before, the gray cells, reflect up to 20% of the
light that hits them, because of the nature of the color
that they are made of. In order to minimize the reflection
and maximize the electrical efficiency, we add on the front
of the cell a very thin layer of titanium dioxide. We trap
more of the light using this titanium dioxide layer. So
some of the light is trapped, goes in, is reflected, comes
back in, and gets more chance of doing some work in the
solar cell. Only the very strong and the very powerful light
, which is the UV, and the blue, is reflected, and we see
them. That is why the cells are blue. "
Dr. Jean Posbic
BP Solar, Maryland
Links
- From Newton’s
Apple, background and activities related to thermal
solar energy, including a solar cooker.
- An excellent resource for teachers on semiconductors,
including principles, lab work, history and assessment.
Reading
Georgios. T. (1997)' Atomic and Molecular Structure in Chemical
Education: A Critical Analysis from Various Perspectives
of Science Education, 'Journal of Chemical Education,
Vol. 74, pp: 922-925.
Using solar energy
"The solar module will live for about
30-40-50 years. This means that it will be generating for
the next 30-40-50 years just free energy. Obviously, that’s
a great advantage for our earth; we have mined a lot of
the fossil energy. This is finally a way of renewing some
of the energy, and being green for the earth."
Dr. Jean Posbic
BP Solar, Maryland
Link
Reading
Hileman, B. , (2000), Oil Firms Act To Curb Climate Change,
'Chemical & Engineering News, Vol. 78, No. 45,
pp: 26-31.
| Proceed
to Unit 3.2 |
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