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Solar photovoltaics: - What happens to the lost energy?

  1. Jul 11, 2017 #1
    I have a very simple question about solar photovoltaic systems. We all know that they have limited efficiency. Suppose there is a module that is 10% efficient i.e. it can convert 10% of sunlight falling onto it into electricity. I just want to know what will happen to the rest 90%? I mean do those just reflect back like a mirror or some change may occur in their composition?
     
  2. jcsd
  3. Jul 11, 2017 #2
    A small amount is reflected but the major portion is degraded into heat.
     
  4. Jul 11, 2017 #3
    As far as I can remember that I have seen photographs of solar cells that shines almost like a mirror. If what you are saying is true, that means that maximum amount of sunlight will be absorbed by the materials of the solar cell. A small portion is converted into electricity and the rest will be radiated as heat. In that case, concentrated solar photovoltaic technology would be simply impossible due to generation of excessive heat.
    As per thermodynamics, maximum amount of sunlight will be converted into heat. But does that mean that the solar cell itself converts the unused sunlight into heat and radiates it?
     
  5. Jul 11, 2017 #4

    russ_watters

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    Look again; they are dark blue (probably from a small amount of sky reflection) or black.
    I think I know what you are trying to ask, so I'll say no even though the answer is yes...
     
  6. Jul 11, 2017 #5
    Kindly give a look at the news.
    The answer is confusing.
     
  7. Jul 11, 2017 #6

    OmCheeto

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    That news is 7 years old.

    Tempers flare over solar panel
    By Anne Pickering Aug 18, 2010

    You should look at new news.

    ps. Have you ever seen my solar panels? They are a beautiful dark blue.:

    2017.07.11.solar.panel.kyocera.png

    And hardly any glare.
     
  8. Jul 11, 2017 #7
    Kindly read this article. For this reason, solar panels now are looking like this. If the amount of reflection is small, why anti-glare glasses are needed. The graph below clearly shows that with increasing angle of incidence, the amount of reflection also increases and at 90 degree, the reflection coefficient is more than 70%.
    That simply means that solar panels reflect sufficiently at that time and special measures are necessary to prevent them.
     
  9. Jul 11, 2017 #8

    OmCheeto

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    You make no sense to me.

    GOOD BYE!
     
  10. Jul 11, 2017 #9

    OCR

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    Lol...
    That's nice ...[COLOR=#black].[/COLOR] :oldeyes:
     
  11. Jul 11, 2017 #10

    russ_watters

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    Haven't you seen glare off of a window/windshield/lake before? The covering of the panel can be 95% clear, but if it reflects 5% of the light straight into your eyes, it will be blindingly bright.
    Solar panels are black, so they absorb light, which makes them get hot. It's that simple. I suspect you were getting at some sort of process related to the generation of electricity that also generates heat, but that's a no.
     
  12. Jul 12, 2017 #11
    In the article, it has been clearly shown how reflection increases with increase in angle of incidence. Solar panels fitted with solar tracking always face the Sun i.e. the angle of incidence for them is always nearly 90°. Do you think that reflection parameters are same for them too?
     
  13. Jul 12, 2017 #12

    Vanadium 50

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    Are you hear for an answer to a question or to push an agenda?
     
  14. Jul 12, 2017 #13

    russ_watters

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    Read it again: it says degrees from normal incidence. That's low angles, not high angles. I ask again: haven't you ever seen glare off anything?
     
  15. Jul 12, 2017 #14
    Can't understand what you want to mean by "normal incidence". I just want to know what will happen for solar panels those are fitted on solar tracking i.e. where sunlight falls on the panel at very close to the highest degree.
    What I want is nothing but a clear answer.
     
  16. Jul 12, 2017 #15

    russ_watters

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    https://www.google.com/search?q=nor...0j69i57j0l4.2829j0j4&sourceid=chrome&ie=UTF-8
    Clear questions help lead to clear answers -- but I think by now you have gotten clear enough answers. It is up to you to absorb them. If you're still not getting how glare works, I have homework for you: next time it is night where you are, get a window, a directional flashlight(spot light) and a flash camera. Create and observe glare.
     
  17. Jul 12, 2017 #16

    davenn

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    you have been given clear answers
    you just refuse to accept them
     
  18. Jul 12, 2017 #17

    davenn

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    time for this thread to close me thinks
     
  19. Jul 12, 2017 #18

    Merlin3189

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    Does that not show simply that the reflection is more specular than diffuse? If that were a mirror standing in the sunshine opposite a dark surface, presumably it would look even darker, with less glare in the top right and from the solder tracks.

    From my reading of the interesting news article it is the specular reflection that is the problem. Even if it is comparable with reflection from windows, as Russ suggests, that doesn't make it any less of a problem. Large arrays of windows are also a problem in some places and still make news here.

    I don't understand why everyone is being so rude towards this poster. His questions seem reasonable and interesting to me and I see no indication of "pushing an agenda" (perhaps you know him and are anticipating something I'm unaware of?) If I think a conversation is becoming fruitless (as many do - even when driven by vip members) .I just leave. I don't feel the need to shout at people or make sarcastic comments.
     
  20. Jul 12, 2017 #19

    russ_watters

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    Last edited: Jul 12, 2017
  21. Jul 12, 2017 #20

    Vanadium 50

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    If the complaint is glare, I might suggest that one should look at the nice polished aluminum frame before the cells themselves.
     
  22. Jul 12, 2017 #21
    The question isn't about glare. The question is whether most of the unused light is reflected back or being absorbed first and then radiated as heat as most suggested here. But, I just suddenly remember that solar cells were first used in space and futurists are thinking of using solar cells as source of electricity in future Moon colonies. Both space and Moon don't have any atmosphere and that means no convection is available. I am wondering how solar cells can protect themselves from overheating in such situation if they first absorb the light and radiate it.
    Russ considers this process like a thermodynamic engine. But I have doubt on that point whether we can consider power generation by solar cell similar to thermodynamic engine or not.
     
  23. Jul 12, 2017 #22
    In space radiation is more efficient in removing heat because their is no insulating layer of air around the panel to trap the heat. Air is a problem for the use of solar panels on the earth's surface..
     
  24. Jul 12, 2017 #23
    They can't. In direct sunlight the surface temperature on the Moon is above 100C degree. Solar cells will get heated to slightly lower temperature since some energy is removed (as electricity) compared to the surface.

    According some articles the temperature of solar panels on the ISS can go as high as 150C degree in direct sunlight.
     
  25. Jul 12, 2017 #24

    russ_watters

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    If necessary some other method of cooling such as sublimation of water (used for astronauts) or geothermal heat pump could be employed, but most likely they would just accept the lower efficiency of the higher temperature of operation.
    I don't consider the process like a thermodynamic (heat) engine. A thermodynamic (heat) engine is a device that converts thermal energy into mechanical work. They involve neither radiation nor electricity and utilize a working fluid, not a solid state device, to do the energy conversion.
    https://en.wikipedia.org/wiki/Heat_engine
     
  26. Jul 14, 2017 #25
    Kindly just read this article.
     
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