Risk in solar energy: Spatio-temporal instability and extreme low-light events in China

The dramatically increasing photovoltaic power generation plays a crucial role in the transformation of energy structure and reducing carbon emission, but also facing high instability risks. Analyzing the spatial and temporal instability of solar energy resources in China, as well as the clustering characteristics of extreme low-light events, is of significant importance in identifying key areas for future development of China's photovoltaic industry and ensuring energy security. We propose a stability index and construct a long time series of solar radiation stability from 1981 to 2022 across China. We also extract the frequency and maximum duration of extreme low-light events and explore their spatio-temporal patterns in China. Our analysis reveals spatially unbalanced solar energy resources and varied temporal trends across China. Solar energy resources exhibit a decreasing trend in the Qinghai-Tibet Plateau, while experiencing an increasing trend in Xinjiang, the Northeast Plain, the Yangtze River Basin, and the southeast coastal areas. The turning point for such trends occurred from the late 1990s to the early 21st century. Notably, the instability of solar energy resources varies across regions, with the Yangtze River Basin and the southeast coastal areas experiencing greater instability compared to the Qinghai-Tibet Plateau, Northwest China, Inner Mongolia, and other regions. Extreme low-light events occur frequently and their spatial distributions vary largely with seasons. The probability of extreme events in Sichuan Basin is completely opposite in spring versus winter. Summer stands out as the season with the highest stability of solar energy resources and the largest total solar radiation across China. The extreme low-light events in a large portion area of China is becoming more intense. China's photovoltaic allocation should pay more attention to climate risks in the future.