Can solar panels be safely short-circuited while they are fully illuminated? I've looked at the specs and I understand the concept of MPP, conversion efficiency, etc. I have no particular design or application in mind where short-circuiting the output plays a role - just that it might be useful to know.
I mean safe for the panel. Please disregard consideration of external circuits.
Usually not a problem. Most panels run close to their short circuit current capability.
They can't get any hotter than a sheet of black stuff.
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I use photodiodes 'short circuited' (into a TIA opamp circuit). It doesn't seem like short circuiting a solar panel could hurt it. (But I've never used one!) It might be useful as the short circuit current would be some measure of the total intensity. Are the panels all just single 'diode drops' or do they sometimes put a few in series?
George H.
Thanks.
I didn't get that right away but let's see (basic college thermodynamics is >40 years in the past). The panel receives solar radiation, much (most?) of which is thermal and the black panel is efficient at absorbing it. So the panel gets heated up quite a bit. But some of the radiant energy is converted to an electrical potential. If that electrical potential is short-circuited, there's no change in the power expended in the cells, and therefore no additional heat produced. Is that the logic?
But then not all the radiation is thermal and the non-thermal part is also converted to electricity. Wouldn't that produce additional heat if it's short-circuited?
I have one panel as a sample and it has 39 cells in series. Judging from the size, I'd guess the power rating as somewhere around 50W. Its open circuit voltage in bright sunlight is about
23V. I haven't tested it yet to plot its characteristics under different levels of load and sunlight. No datasheet, and the company has only a rudimentary website.Someone gave me the sample to play with and see if I could turn it into something useful. It seems they have truckloads of the things but they don't know what to do with them. I didn't bother asking why they bought them in the first place. Probably with some vague idea of using them as backup power.
If you short circuit them they will heat up, there will be the same amount of heating as if you leave them open circuit and unloaded, just via a slightly different mechanism.
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That seems right. The energy has to go somewhere. But when the cell is open circuited there's no energy 'lost' from the cell either. The photo-generated e-h pairs recombind in the silicon. So the cell runs at it's coolist when you are pulling just the right amount of energy out of it.
George H.
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Right!... sorry I should have read to the end of the thread before posting.
(Can you see the temperature rise 'in practice', as opposed to 'in theory'?)
George H.
It was an issue for the builders of the sunshark
In their design the silicon wafers are beneith a layer of fibreglass abd the overheating was causing delamination.
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Not as much hotter as they would get cooler in the shade w/o a short.
Bret Cahill
Except that when they're short circuited the heating may be concentrated in some wire or another and burn it up.
I hadn't chimed in to this thread yet because I suspect that the short- circuit current is close enough to the optimal current that unless the panel is really poorly designed it'll do just fine. But I don't KNOW.
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