Independent thesis Advanced level (degree of Master (Two Years)), 10 credits / 15 HE credits
This study has been carried out to evaluate the degradation of grid connected PV system modules installed at Högskolan Dalarna in Borlänge, Sweden. The system which has two arrays each containing 36 monocrystalline PV modules has been in operation since 1994. The modules from GPV of an average peak power 43.9W were tested for I-V curve characteristics under outdoor conditions using AMPROBE Solar 4000 I-V curve tracer with ±1% accuracy and AMBROBE Solar 4000 Sensor with accuracy of ±5%. Measured electrical parameters (short circuit current, open circuit voltage, and maximum power) were extrapolated to STC following Standards IEC 60904-1 for I-V curve measurement and IEC 60891 for temperature and solar irradiation corrections. Thus, values extrapolated to STC were compared with nominal values to calculate global power degradation.
An average global power degradation showing a standard deviation of 1.6% is found as 11.9% while open circuit voltage and shot circuit current average degradations are 2.5% and 6.4% respectively. Calculated median degradation rate of 0.6% is also compared with a related study median degradation rate of 0.46% per year in similar weather conditions and estimated warranties of 80% of the nominal power after 20 years of operation provided in the 90s. Thus, all the tested modules have a median degradation of 2.5% higher than that of related study and they have shown higher performance as compared to estimated manufacturer’s warranty.
Regarding degradation modes, visual inspection was carried out on each module, except light yellowing or browning in some modules, no visually visible defects or faults like cell crack, delamination, bubbles, hot spot, and rust in connection boxes were displayed. However, the calculated power degradation, depending on the I-V curves deviations found, is induced because of the possible causes by parasitic resistances, mismatch, ageing, and loss of transparency of encapsulant due to light browning.