Temperature and Irradiance Dependence of Current and Voltage at Maximum Power of Crystalline Silicon Photovoltaic Modules
Manit Seapan1, Yoshihiro Hishikawa2, Masahiro Yoshita2, Keiichi Okajima1
1Department of Risk Engineering, University of Tsukuba, Tsukuba, Ibaraki, Japan
/2Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan

The temperature and irradiance dependences of the current and voltage at maximum power point (Imp and Vmp) were analytically and experimentally investigated. The Imp and Vmp were simulated in the range of the series resistance (Rs) of 3 - 7 milliohm and the diode ideality factor (n) of 1.0 - 1.2, which includes typical commercial crystalline silicon photovoltaic (PV) modules. The Imp formula was reorganized by using the one-diode model and was shown to be nearly constant within 1.4% for temperature variation over 10 - 70 °C. The simulation also showed that the Imp is nearly proportional to irradiance (G), and its non-linearity for irradiance was within 0.2% in the irradiance range between 0.5 and 1.2 kW/m2. The simulation for Vmp showed a linear decrease by increasing temperature over 10 - 70 °C. The Vmp was constant within 2.4% with irradiance between 0.5 and 1.2 kW/m2. Since the Imp was shown to be nearly constant with respect to temperature, the voltage-dependent temperature coefficient in ref. [5] can be approximately used for the Vmp-temperature correction. This work investigated the Vmp-temperature correction without current-voltage characteristic (IV curve) information. Experiments of the Vmp-temperature correction to 25 °C for a crystalline silicon PV module showed good reproducibility for 28 days. These results are useful for characterizing the performance of commercial crystalline silicon PV modules by using the Vmp and Imp values. The relation between Pmax and G was also analytically investigated and compared with experiments.