Variation-based complementarity assessment between wind and solar resources in China

•Propose a novel variation-based complementarity metrics system.•Assess the complementarity between wind and solar resources in China.•Test the trend and persistence of the complementarity of wind and solar resources.•Northwest China is the most suitable for renewable energy expansion. The complementarity between wind and solar resources is considered one of the factors that restrict the utilization of intermittent renewable power sources such as these, but the traditional complementarity assessment rely on the strength of the negatively correlated variables and do not consider the scale of those different variables. To this end, we propose a novel variation-based complementarity metrics system based on the description of series’ fluctuation characteristics from quantitative and contoured dimensions. From this, the complementarity between wind and solar resources in China is assessed, and the trend and persistence are tested. Furthermore, the spatial compatibility between wind and solar resources and hydropower resources in China for supporting the expansion of wind and solar power is discussed. The results indicated that (1) there is a complementarity between wind and solar resources throughout China, and the regions rich in wind and solar resources, such as the northwest, north, and northeast of China, usually exhibit a strong complementarity; (2) the complementarity shows an increasing trend during 1961–2016 that was prominent in the northeast, northwest, north, and southwest of China; (3) the persistence or anti-persistence of the complementarity across China is weak, while in comparison, the complementarity in the northwest, northeast and southwest of China is more likely to continue to increase in the future; and (4) northwest China is the most suitable region to develop the hydro–wind–solar hybrid system. Although southwest China has the most abundant hydropower, the relatively low production efficiency and weak complementarity of wind and solar resources may restrict the scale of wind and solar power.