Decadal variability reveals contrasts in solar-resource stability across China

Solar resource assessments traditionally focus on how much solar radiation is available and how it changes over time, while overlooking how stable that resource remains throughout the decades. Here, we quantify the spatiotemporal heterogeneity of decadal variability in downward surface solar radiation (DSSR), commonly known as global horizontal irradiance (GHI) in the solar energy sector, across China’s seven major power grids during 1960–2024. We find pronounced regional contrasts in decadal DSSR variability, with the Central, Eastern, and Southern grids exhibiting greater variability, whereas the Western and Tibetan grids, combine high solar resource abundance with comparatively low variability. The Central and Eastern grids also contribute disproportionately to national variability relative to their geographical area. By converting DSSR variability into indicative photovoltaic (PV) yield, we further illustrate that resource-driven yield uncertainty is substantially higher in the volatile eastern regions; however, spatial diversification across weakly correlated grids can reduce portfolio variability by up to 29%. These findings emphasize that the geography of solar-resource climatic stability differs from resource abundance, highlighting the critical need to incorporate decadal stability and spatial diversification into long-term renewable-energy and inter-regional transmission planning.