Untangling multi-level efficiency evolution in China’s offshore wind power: from project development to electricity generation

• Evaluates offshore wind efficiency via a multi-level two-subprocess framework. • Covers 122 OWPs representing over 95 % of China’s commissioned offshore wind capacity. • Identifies U-shaped technical and S-shaped scale efficiency evolution patterns. • Reveals provincial inefficiencies driven by locational and infrastructural factors. • Links efficiency dynamics to scale economies, ownership, and competitive tendering. Sustaining offshore wind utilization requires continued gains in technical and scale efficiency to optimize resource allocation, accelerate farther-offshore and deeper-sea expansion, enhance energy and economic performance, and mitigate environmental externalities. However, existing offshore wind efficiency studies remain largely engineering-oriented, with limited econometric assessments across different analytical dimensions and organizational levels. Based on 122 offshore wind projects representing approximately 95 % China’s commissioned capacity during 2010–2024, this study conducts a multi-dimensional, multi-level, and two-subprocess efficiency assessment across project development and electricity generation. Project-level technical efficiency follows a U-shaped pattern, whereas scale efficiency exhibits an S-shaped evolution. Project development efficiency is largely determined by lifecycle investment and locational characteristics, while electricity generation efficiency depends more on wind resource availability than installed capacity. Provincially, inefficiency patterns arise from heterogeneous resource endowments and infrastructure, including deep-sea siting challenges in Jiangsu and Zhejiang, construction-induced pollution in Shanghai and Shandong, and insufficient technological scale in Hebei, Fujian, and Guangxi. Nationally, efficiency evolution aligns with three phases of sectoral growth: demonstration (2010–2014), expansion (2015–2020), and commercialization (post-2020), reflected in productivity, newly-commissioned capacity, and grid-connected generation. These efficiency dynamics are shaped by turbine-related scale economies, substructure choices, ownership structures, provincial learning-by-doing, and competitive tendering.