Is there a grid-connected effect of grid infrastructure on renewable energy generation? Evidence from China's upgrading transmission lines

China has built the world's largest power infrastructure. Those upgrading power grid facilities not only contribute to providing enough end-used energy for the world's factories, but also offering a basic guarantee for the clean strategy of Building a Beautiful China proposed by the Chinese government. The national grid system supported by extra-high voltage and ultra-high voltage grids as the backbone makes it possible for a non-dispatchable renewable energy source to be connected to the national grid and transmitted to terminal consumers in load centers. The aim of this paper is to test whether China's advanced power grids have played a positive role in promoting power generation of intermittent renewable energy source. A novel nonlinear estimation named panel smoothing transition regression is introduced to capture heterogeneous effects of grid-connecting renewable energy source across regions. The empirical results show that whereas power grid infrastructure generally enhances power generation of renewable energy source and consumption in energy bases and load centers, the effects change across different voltage levels of power grids. The extra-high voltage power grids show strong support for grid-connecting renewable energy source, while the effect of ultra-high voltage power grids is unexpectedly insignificant. The extra-high voltage power grids have not yet become the backbone of the national grid, which is the main reason for the inadequate grid-connected renewable energy source to the ultra-high voltage power grids, indicating the importance of upgrading the power grid infrastructure.