Precise performance characterization and diagnosis of photovoltaic (PV) modules and strings by using the maximum-power voltage Vmp and maximum-power current Imp during MPPT operation are investigated and verified by simulation and experiments. They are analyzed by using new temperature correction formulas, which take into account the voltage-dependent temperature coefficient of the crystalline silicon PV devices. Slight change in the Pmax under any specified conditions such as STC (1 kW/m2, 25 ºC) can be sensitively detected with precision better than about 1%. Experimental and simulation results indicate that variation of the Vmp and Imp by partial shading caused by various factors such as weeds and nearby PV modules can be also sensitively detected, even when only one cell in the string is partially shaded.
