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We know that solar cells generate electricity utilizing the energy of the photon, but how can they generate electricity forever?

In a n-type terminal we have the bond of silicon and phosphorous so we have a free electron and when photons hit the panel they let the free electrons flow to the p-type terminal which is a bond of boron and silicon which has a free place for an electron.

But when all electrons have moved to the p-type from the n-type, then, how can they generate electricity forever when all electrons are at the p-type terminal? (because both the terminals are neutral)

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  • $\begingroup$ How does solar panels generate infinite electricity. They don't. I'm not an expert, but I know there are mechanisms of energy loss. $\endgroup$ – HDE 226868 Apr 8 '15 at 16:54
  • $\begingroup$ tf.uni-kiel.de/matwis/amat/semitech_en/kap_8/backbone/… circuits usually close and replenish the electrons. $\endgroup$ – anna v Apr 8 '15 at 17:12
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    $\begingroup$ @annav not "usually"; Circuits are closed by definition. Bhavesh, "electricity" is a broad concept. Solar cells can drive an electric current in a circuit (which is closed, by definition). Learn about current flow first. $\endgroup$ – Solomon Slow Apr 8 '15 at 17:53
  • $\begingroup$ @jameslarge I should have used sarc\ $\endgroup$ – anna v Apr 8 '15 at 18:46
  • $\begingroup$ @annav are you telling that solar panels don't generate infinite electricity? $\endgroup$ – Bhavesh Apr 9 '15 at 3:38
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We know that solar cells generate electricity by utilizing the energy of the photon,

This is an every day language, electricity. It means things electrical in general every day language.

but how does it generate electricity forever?

What is generated when the photons hit any material, is heat, and the sun's energy is at maximum 1300Watts per meter square at the top of the atmosphere ( from this atmospheric absorption and reflection must be subtracted), that leaves at maximum less than 1000watts/m^2 on the solar panel. That is the limit of how much energy can be extracted from the sun with any method, water heaters, conservatories and solar panels. So there can be no infinity in any variable, including electrical current from the solar panel.

In n-type terminal we have the bond of silicon and phosphorous so we have a free electron and when photons hit the panel they let the free electrons flow to the p-type terminal which is a bond of boron and silicon which has a free place for an electron

This is the microscopic picture .

but when all electrons move to the p-type from the n-type then how can they generate electricity forever when all electrons are at the p-type terminal? (because both the terminals are neutral)

If you get all the electrons on one side of an object the other side will be positive , and that will be it, no current flowing , just separated charges sitting there. There will be a finite electric field the value dependent on the geometries and the material.

If one closes the circuit, then the electrons can move to the positive side and the cycle can continue as long as photons fall from the sun. A current is created that is used for the "electricity" provided to the home.

The "sun an infinitely renewable source" is an exaggeration of scientific reporting, since the sun has a finite lifetime, except it is so large with respect to our lifetimes that it may be called infinite. The scientific expression should be "a continuously renewable source".

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  • $\begingroup$ If you want to be exact, the sun is not even "a continuously renewable source". I would say that it is a "source". It doesn't renew itself and it is not continuous; it will eventually die. $\endgroup$ – LDC3 Apr 9 '15 at 4:24
  • $\begingroup$ @LDC3 but after millions of years but for now we consider it as renewable source $\endgroup$ – Bhavesh Apr 9 '15 at 4:30
  • $\begingroup$ but annav as you said the process will continue but when all free electrons go from n-type to p-type both become neutral as the n-type had one extra/free electron which goes to the p-type which has one free space for a electron so it becomes neutral. So how does it do a continuous electric current generation? $\endgroup$ – Bhavesh Apr 9 '15 at 4:36
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    $\begingroup$ Have a look at this physics.org/article-questions.asp?id=51 "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". A closed circuit moves charges and generates a current, an open one not. $\endgroup$ – anna v Apr 9 '15 at 4:53
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    $\begingroup$ I don't think you'll get 1300 W/m2 on Earth - only at the edge of the Earth's atmosphere. Peak sun at the surface is usually taken to be 1000 W/m2 $\endgroup$ – EnergyNumbers Apr 10 '15 at 10:13
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When photons from the Sun hit the crystallized silicon wafers in a solar panel, they energize electrons to become loose and make a complete trip around the closed circuit that include the solar collectors. So the solar panels do not lose electrons because they go out from one end and come back in from the other end

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