I am using this circuit to measure the voltage of a small solar panel - around 3 or 4 V max (so instead of the photodiode consider there is a solar panel). That means Vin = -3 V. When I first built it, I didn't think about the fact that the op-amp is single supply and what effects that might have. Today, I was thinking about it and after reading some things, came to the conclusion that a single supply op-amp should not accept voltages outside its rail-to-rail range. I have 2 questions:
Why is the anode of the panel connected to ground and not the other way around? (I based this circuit on one I saw online)
Why does this circuit work? The output is exactly what I expected it to be in the first place (-0.65*Vin), but it shouldn't, because it's a single supply op-amp, right?