I was thinking about a power circuit in which the power can be supplied on the same rail through a solar panel or an ac adapter. I automatically thought to add diodes in series to form an OR gate, so the panel wont supply the ac adapter and vice versa. But then I thought- do I really need to protect the solar panel from reverse current? What would actually happen?

What happens if you supply power to the solar panel, not from it? I would appreciate all help.

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    \$\begingroup\$ Not really, but you will sink a lot of current from your power supply and burn it as heat in the panel. \$\endgroup\$ – winny Aug 29 '18 at 22:04
  • \$\begingroup\$ And I understand that the less light is available for the panel, the more current it will sink? \$\endgroup\$ – Łukasz Przeniosło Aug 29 '18 at 22:05
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    \$\begingroup\$ The solar panel will act like a diode. \$\endgroup\$ – user253751 Aug 29 '18 at 23:08

Your solar panel may already have a series diode to prevent it from sinking current, in which case you're fine. But otherwise, yeah, it will draw reverse current from the supply.

Referring to the standard equivalent circuit of a solar cell, if you exceed the threshold voltage on the shunt diode, the cell will begin to conduct reverse current.

If you've got a commercial solar panel, I believe they typically have reverse protection diodes built in to prevent a shaded panel from sinking current from the rest of the array. You'll want to verify that's the case for the exact panel you're using, of course.


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ I learned today that applying voltage to a solar panel they emit IR light. Does this damage them? \$\endgroup\$ – traisjames Dec 28 '20 at 0:49

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