Apply voltage to a solar cell
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 &ndash; Schematic created using CircuitLab