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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