Investigation of the Temperature Sensitivity of 20-Years Old Field-Aged Photovoltaic Panels Affected by Potential Induced Degradation

Abstract

One effect of moisture ingress on solar panels is potential induced degradation (PID). Solar panels affected by PID experience large leakage currents between the solar cells and the module’s frame, which leads to substantial power degradation. In the present work, the temperature coefficients of 3 old PV panels affected by PID were investigated. In the electroluminescence images, solar cells nearer to the edge of the modules appear darker due to ohmic shunting. IR thermal images acquired under clear sky outdoor conditions show that the majority of the warmer cells (hotspots) were located closer to the edge of the modules. The difference in cell temperature (∆T) due to PID effect ranges from 7 °C to 15 °C for the 3 field-aged modules. The average temperature coefficient of efficiency (βηm) was found to be −0.5%/°C. Also, it was observed that the temperature coefficients of open circuit voltage (βVoc = −0.4%/°C), maximum power point voltage (βVmpp = −0.5%/°C), and fill factor (βFF = −0.2%/°C), were the underlying factors for the degradation in the Pmax of the old solar panels affected by PID. This accounted for an average 1.2%/year overall degradation in the efficiency of these modules. Most notably, it was discovered that the PV modules affected by PID show negative temperature coefficients of maximum power point current (βJmpp) due to large leakage currents. This observed negative βJmpp we believe is characteristic of PV panels affected by PID.

Temperature profiles of field-aged photovoltaic modules affected by optical degradation

“…9 ) along the edges of the PV modules suggests that the presence of PID in these PV modules is likely [ 15 , 16 , 39 ]. According to Segbefia and Sætre [ 36 ], some of these modules have been affected by PID as well.…”

“…In PV modules affected by PID, the β Pmax was found to be closely identical to both β Voc and β FF . However, for the modules affected by PID, the variation in β FF was observed to be greater than 0.3%/°C [ 36 ]. To understand the degree of correlation of these electrical parameters to P max , regression plots of the temperature coefficients were carried out.…”

“…This suggests that optical degradation in PV modules could be monitored more precisely using PV module's β Voc and β Vmpp . However, the effect of β Voc and β Vmpp on β Pmax also depends on other co-defects [ 27 , 36 ]. The regression plots of PV module efficiency ( η m ) versus T m for the optically degraded PV modules are shown in Fig.…”

“…In addition, moisture ingress can also cause PID [ 15 , 16 , 39 ]. PV modules affected by PID were found to show characteristic negative β Jmpp [ 36 ]. It was observed in Sections 3 , 3.3 .4 that PV Module C was affected by PID.…”

“…The electrical characteristics of the 3 selected modules and the manufacture's data sheet values are presented in Table 1 . The information on the modules and solar cells has been presented earlier [ 5 , 36 ].…”