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What's actually happening in the photovoltaic effect

  1. Dec 29, 2008 #1
    The standard conception of the photovoltaic/photoelectric effect is that photons are absorbed by the receiving medium, knocking loose electrons, which form a current away from the receiving medium.

    However, it seems that this can't be what is actually happening because solar panels, for example, can last decades and there are of course not enough electrons in the panels themselves to be constantly knocked loose into a stream of electrons.

    It seems more accurate to state that photons (conceived as simply the electromagnetic "message") are absorbed by the panel and that the electrons, which are matter particles, are induced to vibrate at a higher rate. This vibration is then passed on to other electrons in the connecting cable and the vibration (motion) is what is actually passed from panel to cable to electricity load.

    Any thoughts on what is actually going on here?
     
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  3. Dec 29, 2008 #2

    Vanadium 50

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    Well, when you have a current, you have as many electrons moving in one side as moving out the other side. So there's no risk of "running out" of electrons. Indeed, the actual velocity of electrons is quite small: around 1 mm/s, so it takes quite some time before the electrons are "replaced".
     
  4. Dec 29, 2008 #3
    Vanadium, it seems that what you write runs into the same difficulty I mentioned in my first post: even if electrons move slowly, there are no where near electrons in a solar panel to last thirty or forty years. So even if you have as many electrons going "into the pipe" so to speak as come out of the pipe, where do the electrons come from?
     
  5. Dec 29, 2008 #4

    turbo

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    Treat the cell as if it were a battery. The sunlight increases the potential on one pole of the battery, which can give up free electrons, and the other "pole" of the battery receives electrons in return. Both poles are in the circuit, so the net number of electrons in the cell does not change.
     
  6. Dec 29, 2008 #5
    Turbo, in your conception, are you saying there is a constant circular flow of electrons between the poles? If so, how is the current transmitted to a wire, and then from the wire to, say, a computer? Are you suggesting that each part of the chain consists of a confined and circular flow of electrons?
     
  7. Dec 29, 2008 #6

    turbo

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    The difference in potential at the cell can cause a flow of electrons. That flow can be used to charge batteries (to exploit the electro-chemical potential of batteries). Do you agree that this cannot happen unless BOTH poles of the cell and BOTH poles of the battery are in the circuit? If not, I'll have to cut this off here.
     
  8. Dec 29, 2008 #7

    Vanadium 50

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    This is not specific to photovoltaics - any circuit has as many electrons going in as coming out. They are in the material of the circuit; electronics is the field that describes how they move around.
     
  9. Dec 29, 2008 #8
    Turbo, the question I'm seeking some help with goes to the ontology of electrons and photons. I'm trying to figure out what it means to describe an electron flow stimulated by photon absorption. As I've stated, it cannot be the case that a constant flow of electrons is emitted by a solar panel or a battery unless they are being created with the absorption of photons. Alternatively, we can envision the vibratory motion of electrons in each step in the circuit being transmitted to the next electron, and so on, rather than a flow of electrons, per se. Electromagnetism may be envisioned (and I believe it is probably a more accurate conception) as the motion of charged particles, rather than as a thing in itself. As such, electrons move (vibrate) in response to the various other charged particles in their sphere of interaction. In this conception, the photon from the Sun isn't a thing, per se, it's simply a packet of information that tells other charged particles how to move. In our solar panel example, the "photons" the panel "receives" simply tell the electrons in the panel to vibrate faster. And this vibratory motion is transmitted to a connecting cable's charged particles, and so on.

    There are a number of issues that arise from this alternative conception: 1) How is the information that consists of the "rules" of EM transmitted between charged particles? 2) If a solar panel is not connected to a cable, how is the increased vibratory motion of the electrons manifested?

    On 1) My working hypothesis is that the information consisting of the rules of EM (and all other forces also) is transmitted through the ether. It's interesting that you have quoted Einstein's 1924 paper On the Ether in your signature because I have recently been researching the various conceptions of the ether in the last century. As you know, Einstein did assert the validity of various conceptions of the ether during his career, despite his 1905 expulsion of the luminiferous ether from physics. His later ruminations on the ether were quite different and he acknowledged from 1916-1924 that a concept of the ether as, at the least, the basis for distinguishing acceleration from rest, was logically necessary. He rejected Mach's notion that inertia and acceleration were a result of the gravitational field of all the mass in the universe b/c this notion implied instant action at a distance. Einstein later again turned away from the ether, even in the stripped down form he advocated for from 1916-1924, arguing instead that a unified field theory could dispel the distinction between matter and the ether that was a consequence of general relativity. More to the point, I do accept the necessity of some conception of the ether, and it is the ether in my working theory that transmits the information consisting of the EM force. As such, it is not detectable in any fashion without some intervening matter. It is only through interaction with matter that the various forces are detectable.

    2) I don't know enough about Maxwell's equations or about solar engineering to know what the distinction is between a solar panel connected to a cable and one that is not connected. Do you have any insight on this?
     
  10. Dec 29, 2008 #9

    turbo

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    In some materials, the electrons are VERY loosely bound, and can be knocked loose with very little energy input. You only have to know this, and that people have designed batteries to leverage the electro-chemical potential so that the batteries can be charged by subjecting them to reverse potentials (vs their operating orientations). Once you can draw the circuit and imagine how current flows between solar-cell and battery, you should get it.
     
  11. Dec 29, 2008 #10

    Vanadium 50

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    Two comments - one is that Physics Forums has rather clear rules about non-mainstream theorizing and overly speculative posts here. The other is that before creating your own theory to replace the conventional theory, it would be useful for you to understand what the conventional theory is and what it says (e.g. Maxwell's equations).
     
  12. Dec 29, 2008 #11

    turbo

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    I'm not going to get into this here. We understand electricity well enough at this point to be able to address it cogently with classical physics.

    There may be some puzzles with gravitation and EM propagation that need to be resolved down the road, but they can wait for now.
     
  13. Dec 30, 2008 #12
    Vanadium, the fact that I've asked a basic question about the mainstream conception of the photoelectric effect and you and Turbo have not supplied a direct answer yet should suggest that there is something wrong with the mainstream conception. I'm not suggesting that Maxwell's equations are wrong - to the contrary, I assume they're correct. What I'm getting at is not the validity of the equations, but the interpretation of the equations and, in particular, the photoelectric effect. That is, what is the actual underlying reality being described by the equations? Physics should attempt to describe reality, not simply satisfy itself with approximations of reality simply because they work well enough. It is, in my view, only through returning to a realist point of view re the practice of science - as opposed to the positivist/non-philosophical view that seems to dominate nowadays - that we will be able to make the breakthroughs required to make progress on the many outstanding problems in physics today. If you haven't read Smolin's The Trouble With Physics, Isaacson's Einstein: His Life and Universe, or Moffat's Reinventing Gravity, I highly recommend them.
     
    Last edited: Dec 30, 2008
  14. Dec 30, 2008 #13
    Turbo, similar to my response to Vanadium, you surely know well that there are large and looming problems with today's physics. Your final statement sounds curiously like Kelvin's musing about reaching the end of physics in the latter part of the 19th Century. Smolin points out in his The Trouble With Physics that there are major unsolved problems in physics today and a growing awareness that the whole structure is built on untenable and sometimes contradictory postulates. In particular, going back to the ether, you are probably aware that special relativity was developed in order to relativize electromagnetism. So while Einstein dispelled the ether in his 1905 SR paper as "superfluous," he realized later that some version of the ether was very necessary. And then he realized that by accepting the ether, even merely as a metric field by which acceleration could be distinguished from rest, he undermined relativity more broadly. And he spent decades trying to develop a good field theory that would reconcile relativity with a non-ether theory. He failed in this endeavor because, in my view, he failed to recognize that we do in fact have two realms that physics needs to examine: the actual world, comprised of the particles studied by the Standard Model, and the potential world, comprised of the ether/ground of being, which also acts as the transmitting medium for what we commonly describe as energy.
     
  15. Dec 30, 2008 #14

    Integral

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    Tam,
    Your question has been answered. Read Vanadium 50 posts over and over until you actually understand what he is saying.

    Thread locked
     
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