There is a growing need for the precise outdoor performance measurement of photovoltaic (PV) modules for low-cost onsite performance measurement, monitoring, and failure diagnosis. For the precise evaluation of a PV module, an accurate temperature measurement technique is required. It is necessary to measure the temperature of the solar cell in a module structure ( junction temperature) because it determines the temperature characteristics of the PV module, rather than the temperature of the backsheet. In this study, a PV module with an internal thermocouple was fabricated. A thermocouple was inserted immediately below the solar cell so that it could be in direct contact with the cell, enabling an accurate temperature measurement. Moreover, the temperature of the solar cell in the PV module structure was predicted by heat flux calculation using the backsheet temperature, which can be measured easily. In this manner, the solar cell temperature was estimated accurately within an error of +1 °C.
Potential-induced degradation (PID) of full-size photovoltaic (PV) modules based on n-type monocrystalline Si solar cells was observed in practical outdoor PV systems in the short term. The maximum power output of the module decreased by about 14% after 12 days of outdoor exposure with application of about −115 V. In contrast, no degradation was observed after +115 V application in the outdoor system. These results indicate that the PID of the n-type Si PV module is easily induced by applying a lower negative potential that does not induce the PID of p-type Si PV modules in outdoor systems. Results suggest that water on the top of the modules during/after a rain, which increases the leakage current between the Al frame and the Si solar cells, is the predominant factor causing the PID of n-type Si PV modules exposed outdoors, rather than temperature and humidity.
Annual trends of indoor output measurement (Pmax(stc)) results of photovoltaic modules exposed outdoors in Tosu city from 2012 to 2022 were investigated. The Pmax(stc) of mono-Si (E-1A), as conventional Si modules, was almost unchanged from 2012 to 2022, however, that of mono-Si (E-1B), as conventional Si modules, was decreased from after 2019. In case of Si heterojunction modules, the degradation rate is expected moderately with prolonged exposure. In case of passivated emitter and rear cell (PERC) modules, it was found that characteristics due to light and elevated-temperature induced degradation (LETID) were observed with good reproducibility in 2021 and 2022.
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