Performance Degradation of Mono and Multicrystalline Silicon PV Modules in Rural Grid-Connected Systems in Southern Brazil
Abstract
The purpose of this paper is to compare the performance degradation of photovoltaic (PV) modules installed on three rural properties in southern Brazil. PV modules with monoand multicrystalline Si solar cells from the same supplier were used. The power degradation rate (DR) was determined from the temporal evolution of the temperature-corrected performance ratio (PRSTC) during the initial years of operation and from measurements of the I–V characteristics of reference PV modules under standard test conditions using a flash solar simulator. The monocrystalline silicon modules presented the lowest annual degradation rate, approximately 0.9% per year, whereas the multicrystalline Si modules presented an average degradation rate of 1.6% per year. The degradation rate determined for one PV system (system A) based on the temporal evolution of the PRSTC was consistent with the values obtained from electrical measurements of the PV modules. In two systems (B and C), the PRSTC method presented DR values in the range of approximately 55%70% higher than those obtained from the I‒V curve measurements of the reference PV modules. Soiling ratio estimated by measuring the electrical parameters of the PV modules before and after cleaning yields average values of 1.3%, 2.0% and 4.0% for the reference modules installed in PV systems A, B and C, respectively. Applying a correction in the PRSTC to consider the average soiling reduced the difference between the DR calculated using both methods by approximately 40% for systems B and C but still substantially differed from the degradation rates obtained via the measurement of the electrical parameters of the reference modules.
Keywords
PV degradation, crystalline silicon, performance ratio, rural grid-connected systems