Energy Droughts in Solar PV Generation Caused by Snow Cover

Snow cover significantly impacts the energy generation of solar photovoltaic (PV) systems, often leading to prolonged periods of low energy production, or "energy droughts." These events are critical to understanding the reliability of PV systems, particularly in regions prone to snow accumulation. In this study, we analyze the effect of snow cover on solar PV generation across Poland for the year 2023 using data from meteorological stations, real PV systems, and multiple modeling approaches. Our analysis utilizes daily snow cover data from 681 meteorological stations, of which 118 were selected based on data completeness. Additionally, sub-hourly (15-minute) data from 174 real PV systems were collected, with 129 systems included in the final analysis due to achieving 95%+ data completeness. The real PV generation was compared against estimates derived from three modeling sources: the JRC PV-GIS tool (using SARAH3 and ERA-5 datasets) and Renewables Ninja (using MERRA-2 reanalysis).The results reveal a significant overestimation of PV generation by the reanalysis-based data sources during the days with snow cover. On average, for a day with an 11 cm snow cover, measured PV generation was only 0.33% of the generation observed on snow-free days. In contrast, MERRA-2 suggested 5.36%, ERA-5 estimated 3.52%, and SARAH3 provided the most accurate estimation at 1.18%, though it still overestimated real generation by nearly a factor of 4. On another snow-covered day with a 15 cm snow depth, real PV output was only 0.98% of typical snow-free generation. However, ERA-5 estimated this output at 58.75%, MERRA-2 at 14.7%, and SARAH3 at 7.98%.These discrepancies highlight a systemic tendency of reanalysis (and also satellite measurements) based tools to overlook the magnitude of low-generation events caused by snow cover. Such overestimations could lead to inaccuracies in energy yield predictions and hinder effective planning for both small- and large-scale power systems. The findings underscore the need for enhanced PV system modeling that accounts for snow-related energy droughts, ensuring greater accuracy in assessing the reliability and resilience of solar energy systems in snowy regions.This study provides valuable insights for improving the integration of PV systems in power systems modeling, emphasizing the critical need for accurate snow-cover correction mechanisms in widely used solar generation estimation tools.

 

The results reported here build on the works conducted as a part of the project no. 2022/47/B/ST8/01113 funded by the National Science Centre (Narodowe Centrum Nauki) titled: Method to quantify the energy droughts of renewable sources based on historical and climate change projections data. A complementary part of this work also refers to no. BPN/BEK/2023/1/00278 funded by the National Agency for Academic Exchange (Narodowa Agencja Wymiany Akademickiej) titled: Harvesting the Elements: Investigating the Economic Value of Complementarity Between Solar and Wind Energy Resources in Large-Scale Power Systems under Extreme Events