As series resistance increases, the voltage drop between the junction voltage and the terminal voltage becomes greater for the same current. The result is that the current-controlled portion of the I-V curve begins to sag toward the origin, producing a significant decrease in the terminal voltage V and a slight reduction in I, the short-circuit current. Very high values of R will also produce a significant reduction in I; in these regimes, series resistance dominates and the behavior of the solar cell resembles that of a resistor. These effects are shown for crystalline silicon solar cells in the I-V curves displayed in the figure to the right.
Losses caused by series resistance are in a first approximation given by P = VI = IR and increase quadratically with (photo-)current. Series resistance losses are therefore most important at high illumination intensities.