Tuesday, 25 July 2017

Power produced and internal resistance of solar cell vs distance from light source


Solar cell can be modeled (rudimentally) as a DC voltage generator $Vp$ with internal resistance $Rp$. Consider a solar cell at a distance $d$ from a (constant) light source.


What kind of relation is there really between produced power $P=\frac{V_p^2}{R_p}$ and $d$?


I found on different sites that it should be $P \propto 1/d^2$ since the light power incident on the cell $P_{inc}$ is proportional to $1/d^2$. I'm ok with that but since $P$ is not the power incident on the cell but the produced power, it is related to $P_{inc}$ by the efficiency $\eta$, that is $P=\eta P_{inc}$.


Therefore $P \propto 1/d^2$ implies that $\eta$ does not depend on $d$! And that seems strange: is $\eta$ really a constant tipically?


Moreover, while it is clear that $V_p$ varies with distance, is it the same for $R_p$? Does $R_p$ also change with distance from light source?





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