The impact of wind-solar capacity ratio on the technical and economic feasibility of a coal chemical coupled off-grid/weakly grid-connected green hydrogen production system

The coal chemical industry requires a stable and continuous hydrogen supply, yet it predominantly depends on gray hydrogen derived from fossil fuels like natural gas and coal cracking, which contradicts energy-saving and carbon reduction objectives. By establishing wind-solar power plants in coal mining areas and integrating renewable electricity with electrolysis-based green hydrogen production in off-grid or grid-connected systems, a source-network-hydrogen system can be created to directly supply downstream coal chemical industries. The integration of coal chemical industries with green hydrogen production enables the organic combination of coal mining, coal chemicals, and renewable electricity, marking a critical pathway for the decarbonization of the coal chemical sector. This study examines hydrogen demand scenarios in the coal chemical industry and develops a simulation model for capacity matching and scheduling of a green electricity-based hydrogen production system. It evaluates optimal capacity matching schemes and assesses technical-economic feasibility across configurations such as varying wind-solar ratios, grid-connected versus off-grid systems, and the inclusion or exclusion of energy storage. The results show that, while ensuring a stable hydrogen supply to downstream users year-round, an optimal wind-solar capacity ratio exists that significantly reduces energy storage requirements without compromising economic performance or energy efficiency. The off-grid hydrogen production system with battery storage achieves optimal performance when wind power constitutes 50 % of the energy mix. Compared to sole photovoltaic and sole wind power systems, the electrolyzer, hydrogen storage tank, and battery capacities are reduced by 42.3 % and 21.2 %, 16.4 % and 12.2 %, and 76.6 % and 65.7 %, respectively. System costs and electrolyzer downtime are reduced by 59.3 % and 45.8 %, and 24.1 % and 10.5 %, respectively. In the grid-connected system, the optimal configuration is achieved when wind power accounts for 75 % of the energy mix. Compared to sole photovoltaic and sole wind power systems, the electrolyzer, battery capacity, and grid-down electricity ratio are reduced by 45.4 % and 21.2 %, 14.9 % and 13.4 %, and 78 % and 54.2 %, respectively. When wind power constitutes 75 %, the Levelized Cost of Carbon and electrolyzer downtime are reduced by 58.5 % and 15.8 %, and 53.4 % and 35.6 %, respectively. However, in off-grid hydrogen production systems without energy storage, wind-solar hybrid power generation can cause frequent start-stop cycles in hydrogen production equipment. This indicates that integrating battery storage or grid connection into renewable energy-based hydrogen production systems is more compatible with wind-solar hybrid power generation. This study offers valuable insights for designing green electricity-based hydrogen production systems in the coal chemical industry and provides guidance for determining the optimal wind-solar ratio.