Renewable energy, intelligent manufacturing investment and regional economic development in China: Evidence from low-carbon transition practices

China’s dual commitment to achieving carbon neutrality by 2060 and peak emissions before 2030 has catalysed an unprecedented co-deployment of renewable energy investment and intelligent manufacturing systems across its provincial landscape. Despite the scale and strategic significance of this parallel transition, the joint macroeconomic and spatial consequences of combining renewable energy investment with intelligent manufacturing investment have not been rigorously analyzed in a unified empirical framework. This paper fills that gap by delivering a comprehensive empirical analysis of how renewable energy investment (REI) and intelligent manufacturing investment (IMI) interact to shape regional economic development, green total factor productivity, industrial structure upgrading, and carbon emission intensity across 30 Chinese provinces from 2005 to 2022. Employing a dynamic spatial Durbin model, the pooled mean group estimator, system GMM, and a double-threshold panel regression, the study derives four principal findings. First, REI and IMI each exert significant positive direct effects on provincial GDP per capita growth, with coefficients of 0.34 and 0.29 respectively, and these effects are amplified by a statistically robust synergy term (0.18, p < 0.01). Second, both investment types generate meaningful spatial spillovers, with the combined indirect effect accounting for approximately 35 percent of the total growth impact. Third, a double-threshold regression conditioned on low-carbon policy intensity identifies two structural breaks at policy intensity values of 0.35 and 0.68, revealing that the joint RE-IM growth effect is strongest under high policy intensity regimes. Fourth, sigma-convergence analysis confirms that provinces with above-median RE-IM composite indices exhibit income convergence rates approximately 1.6 percentage points per year faster than below-median provinces, establishing the dual investment strategy as a force for regional equity. Green TFP decompositions attribute approximately 60 percent of frontier-shift productivity gains in high-intensity provinces to the RE-IM technology synergy. These findings provide actionable evidence for the design of China’s coordinated low-carbon industrial policy, spatial energy planning, and regional equalization strategy.