Advancing solar and wind penetration in China through energy complementarity.

The intrinsic variability of solar and wind energy, compounded by their rapid expansion, has intensified power curtailment challenges1,2. Although spatiotemporal complementarity between these resources is widely recognized as a pathway to enhance renewable integration and reduce balancing requirements3-16, existing assessments are largely based on hypothetical deployments17-24. Consequently, how solar-wind complementarity manifests under real-world infrastructure and shapes system-level integration outcomes remains unclear. Here we develop a unified national inventory to enable a data-driven assessment of solar-wind complementarity. The inventory covers 319,972 solar photovoltaic facilities and 91,609 wind turbines in 2022, identified from sub-metre satellite imagery using a deep-learning-based framework. Using this dataset, we show that solar-wind complementarity substantially reduces generation variability, with effectiveness increasing as the geographic scope of pairing expands. At the system level, nationwide inter-provincial coordination raises effective renewable penetration by 99.88 TWh in an 80% dispatchable-flexibility system, corresponding to 9.1% of total solar and wind generation, or approximately 120 h of national average load. These findings demonstrate that energy complementarity is a scalable, system-wide mechanism for advancing solar and wind penetration, offering broadly applicable insights into the role of inter-regional coordination in enhancing renewable integration in large power systems.