The J-V characteristics (J is current density, i.e. current per unit area) of a solar cell under illumination are obtained by shifting the J-V characteristics of a diode in the dark downward by Iph. Since solar cells are designed to supply power and not absorb it, the power P = VIph must be negative. Hence, the operating point (Vm, Jm) is located in the region where and , and chosen to maximize the absolute value of the power |P|.
