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I couldn't find any answer on this super basic question.

Some people on the internet say that you would not put a solar cell in an array under bias, others say that they bias themselves, but I don't understand how this would work: In a series circuit a solar cell would be biased by the adjacent solar cell, right? And it would be a reverse bias, correct? (Since + and - meet.) But then there is also a paper saying that reverse bias is detrimental, or is it meant in a way that there is a "healthy" reverse bias (normal working condition) and a "pathological" reverse-bias (shunt resistances --> hot spots) ?

Please help me understand this, I am getting really desperate over this and can't find anyone who knows something about it.

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  • $\begingroup$ Where on the Internet do you find all those statements? You mention a paper, which paper? $\endgroup$
    – Urb
    Commented Oct 14, 2020 at 14:26
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    $\begingroup$ Here are my sources: "Some people on the internet say that you would not put a solar cell in an array under bias" bit.ly/351agzu (Jim Murphy's comment) "others say that they bias themselves" See Robert Mueller's comment on the same page. Here is the paper I referred to (right at the beginning of the introduction): juser.fz-juelich.de/record/16862/files/FZJ-16862.pdf $\endgroup$
    – AskingBecauseIHaveQuestions
    Commented Oct 14, 2020 at 14:55
  • $\begingroup$ Running a solar cell across the range of open circuit to short circuit gives you the response curve which is important for understanding performance. But going through the effort of biasing large solar energy installations is not particularly useful. $\endgroup$
    – Jon Custer
    Commented Oct 14, 2020 at 16:27
  • $\begingroup$ Okay, but an individual solar cell will still experience an external voltage due to being in series with two other solar cells? And a varying load will also change the voltage. What exactly do you mean by "response curve"? There is no mention of it in my textbook (Solar Energy, A. Smets, 2016) $\endgroup$
    – AskingBecauseIHaveQuestions
    Commented Oct 14, 2020 at 18:15
  • $\begingroup$ A solar cell in a stack of other cells is floating - it will not see an external voltage. $\endgroup$
    – Jon Custer
    Commented Oct 14, 2020 at 18:39

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Solar cells are photovoltaic devices: they develop a photo-voltage when illuminated. In this sense they bias themselves. But that is a very confusing way of thinking about the as components in an electrical circuit.

To get useful power out of a solar cell you must apply forward bias. The optimum bias is at the maximum power point (peak of the dashed curve).

The IV curve (solar black line) of an illuminated diode enters three (two shown in the diagram) quadrants:

  • Negative current, negative (reverse) voltage: photodetector
  • Positive current, positive (forward) voltage: solar cell
  • Negative current, positive (forward) voltage: light emitting diode

IV curve

For more background on this read this site, https://www.pveducation.org/pvcdrom/solar-cell-operation/iv-curve

The same principle applies when the solar cells are interconnected in a solar module. There will be additional current and voltage matching constraints depending on how the module is interconnected, but the shape of the IV curve will still retain this fundamental feature of three quadrants.

I recommend you answer your own question by playing around with a very simple SPICE model of a single solar cell. Then make it more complicated by connecting multiple devices in series and then in parallel and see how the IV curve changes.

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  • $\begingroup$ But why are they in a reverse bias in a series circuit, when they produce power only under forward bias? :/ (Reverse bias, because the adjacent cells have the opposite direction of electric field.) $\endgroup$
    – AskingBecauseIHaveQuestions
    Commented Oct 17, 2020 at 10:17
  • $\begingroup$ I understand what you mean. Maybe you can add you le reasoning to the the question? You should play around with a SPICE model. When connected in series the voltage adds and the current following through each cell is the same (just like series connected batteries). Adjacent cells are not in reverse bias. Don’t understand that part. $\endgroup$
    – boyfarrell
    Commented Oct 17, 2020 at 10:27
  • $\begingroup$ I don't have any experience with using such modeling software. :/ And I think I still have many basic understanding problems: Is it even correct for me to say that solar cells in a series circuit are under reverse-bias, because the n-type region is connected (of course not directly) with a p-type region? (As long as there is illumination, otherwise there shouldn't be any voltage .... or would it be the voltage established by the internal electric field?) $\endgroup$
    – AskingBecauseIHaveQuestions
    Commented Oct 17, 2020 at 10:33
  • $\begingroup$ Yeah that’s the problem. That’s not how it works. n-type and p-type semiconductors are neutral they are not charged negative and positive regions. $\endgroup$
    – boyfarrell
    Commented Oct 17, 2020 at 10:47
  • $\begingroup$ But isn't it different during illumination? Shouldn't they be reverse-biased by the other adjacent illuminated cells? $\endgroup$
    – AskingBecauseIHaveQuestions
    Commented Oct 17, 2020 at 11:44

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