Modified Electrical Model of MJSC for Concentrated Photovoltaic under Changing Environmental Conditions

Abstract

This paper presents a mathematical model for a Multi-Junction Solar Cell (MJSC) that achieves higher efficiency and improved temperature characteristics compared to conventional SCs. The model is based on the single (SD), double (DD) and triple diode (TD) equivalent circuit models used to represent SCs. An additional term representing avalanche breakdown voltage was incorporated into the model. The electrical parameters of the MJSC were studied over a range of concentration ratios (C_r) from 20X to 1000X, direct normal irradiance intensities from 200 W/m2 to 1000 W/m2, and cell temperatures from 15°C to 100°C. The parameters studied included open-circuit voltage (V_oc), short-circuit current (I_sc), maximum power (P_max), fill factor (FF), and efficiency (?). The results showed that all electrical parameters increased with radiation up to a 500X, after which the FF started to decrease reducing cell efficiency. From 500X to 1000X concentration, Voc, Isc, and ? increased from 3.1V to 3.2003V, 6.8A to 13.6A, and 37% to 37.5%, respectively. Higher cell temperatures reduced performance as Voc decreases linearly with temperature. The temperature coefficients of Voc and Isc were determined to be around -5.4mV/°C and 4mA/°C respectively at 500X concentration. Total efficiency decreased at a rate of approximately 0.03%/°C as temperature increased. The model demonstrated that the MJSC design achieves higher efficiency than conventional cells over a wide range of operating conditions due to improvements in voltage, current and temperature characteristics.