A comparison of the performance ratio and degradation rate for two industrial scale PV systems in Nordic conditions

Abstract

The performance and degradation of photovoltaics is important. To receive investments, the solar bankability of the system must be assessed. A high degradation rate causes the risk to be high, which increases the interest rate, and lowers the chance for adaptation. The methods for the calculation of the performance and degradation are not always compatible however, due to differences in the climate and the weather conditions.

In this thesis the performance ratio (PR), corrected performance ratio (CPR) and year on year (YoY) degradation was calculated for two locations in Norway, at ASKO Vestby and ASKO Hedmark. The PR and CPR were calculated using python, and the degradation rate was calculated using a python library called RdTools. To perform the analysis, the data was preprocessed using filters and removing outliers. Most of the time was used to tweak the filters then checking the changes before the data could then be used to calculate the metrics for the analysis.

The results show that ASKO Vestby has had a very consistent performance where the yearly Corrected Performance Ratio (CPR) was hovering around 90% for most of the period, with a maximum of 92.5% and minimum of 89.2% for a period of 8 years. The stability of the performance caused the yearly degradation rate overall to be 0.37%.

ASKO Hedmarks performance has had higher variance, where the CPR was at around 99% 2018 to 2020 and lowering down to 90% at 2023 with a maximum of 99.3% and minimum of 90% for a period of 6 years. This higher variance, combined with the fact that the performance was surprisingly high for the first years caused the yearly degradation overall to be 1.56%. A quick analysis of the potential effects of the high degradation was also done.

The conclusion for this study is that ASKO Vestby is performing well, and slightly better than expectation, and that ASKO Hedmark is still performing decent, even though the degradation seems very high. This is most likely due to the high performance during the early years before it fell to more expected levels. More data is required to see if ASKO Hedmarks performance will stabilize, or if the high rate of degradation continues.