Deciphering Degradation: Utilizing Irradiance Data to Assess Typical Solar Production Degradation in Massachusetts
Objective: Our goal was to assess the typical degradation rate experienced by large (>1 MW) solar facilities in Massachusetts. Our analysis assesses the “all-in” degradation rate, which is inclusive of both typical PV degradation as well as O&M issues. This analysis can contribute to a better understanding of solar facilities’ production profiles and the importance of O&M with respect to a facilities’ production.
Methods: We utilize a sample of 25 facilities ranging from 1 MW to 6 MW with uninterrupted production data beginning in 2013. To assess the average production profile of the sample, we index each facilities' production to allow for comparisons across facilities of varying capacity. These production indexes are then adjusted using an index of historic irradiance data to normalize for the effects of weather. This lets us observe the average percentage change in year-to-year production across our sample, sans variations in weather. To address the effects of snowfall, winter months are omitted from analysis. A separate analysis is performed by breaking the sample into high-variance and low-variance groups to better assess the range of typical outcomes.
Results: Results indicated that facilities typically experience startup issues, with peak production occurring one year into operation. The average degradation rate following this one-year startup period was 1.6%. Results indicate that degradation rates vary substantially across facilities. For instance, our high-variance group exhibited a two-year startup period followed by a degradation rate of over 3%.
Conclusion: Our results suggest that real-world degradation rates are well above those typically assumed by the solar industry (1% to 0.5%). This finding suggests that O&M practices have considerable influence over a facilities’ production profile. By adjusting our results to account for the effects of weather, we provide a unique contribution to the understanding of solar degradation.