A solar panel with surface .8 m × .5 m. can deliver 2.5[A] at 15[V] in full sun (with intensity 800[W/m²]).
a) Compute the efficiency at which this solar panel converts solar energy into electrical.
b) Determine the resistance of R1 ... see diagram.
{Note that it is an active device ("sensor"); in typical use, the current is "almost linear" with light intensity, while voltage remains "almost constant".}
I know the efficiency is 11.7 % and I got R=6 ohms for my answer to part B but it says R is wrong. The other hint it gave me is that there is other resistance in series with R1.