Abstract
This paper presented whether Na ion in the front cover glass is absolute root cause of potential-induced degradation (PID) for p-type crystalline Si photovoltaic (PV) modules or not. P-type monocrystalline Si PV modules with and without the front cover glass, and with and without intentional Na contamination were subjected to PID test. Even without the front cover glass, a decrease in shunt resistance which is a characteristic feature of PID for p-type crystalline Si PV modules has been observed. Intentional Na incorporation on the cell or encapsulant also brings about remarkable PID. These results indicated that Na ion in the front cover glass is not a necessary condition for PID. Furthermore, PID occurs regardless of origin of Na ions. Relationship between PID and leakage current will be also discussed.
Highlights
Potential-induced degradation (PID) is one of the degradation behaviour of photovoltaic (PV) modules exposed outdoors
These findings suggest that PID occurs without Na ions in the front cover glass, drift of Na ions in the front cover glass to the encapsulant may promote PID
This means that Na contamination on the cell surface is the dominant origin of PID for PID-prone cell and the contribution of Na ions in the front cover glass to PID cannot be distinguished
Summary
Potential-induced degradation (PID) is one of the degradation behaviour of photovoltaic (PV) modules exposed outdoors. PID is caused by leakage current flowing between Al frame and cell due to high system voltage.[1,2,3,4] The most likely mechanism of PID of p-type crystalline Si (c-Si) PV module is the shunting effect and the transporting cations to the p-n junction.[5,6,7,8] the relationship between PID and cation (containing Na) remains unknown. Masuda et al have reported the PID test results for PV modules using an ionomer encapsulant instead of ethylene vinyl acetate (EVA) and Na diffusion. The module without the front cover glass were compared. The module structure without the front cover glass and with intentional Na incorporation on the cell or the encapsulant was employed. We investigated how much quantity of Na contaminates the cell surface
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