Teacher resources and professional development across the curriculum

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Sub Image2:Macro to Micro Structures
         
 
Workshops
1) Atoms and Molecules2) Macro to Micro Structures 3) Energetics and Dynamics
4) Theory and Practice in Chemical Systems5) Chemical Design6) The Chemistry of Life7) Chemistry and the Environment8) Chemistry at the Interface
 

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 arrow
 
 

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