Energy, exergy, economic and environmental (4E) analysis of a solar-coal hybrid system with calcium-looping thermochemical energy storage and carbon capture for power and methanol coproduction

China's ‘carbon peaking and carbon neutrality’ goal demands for more renewable energy and less fossil energy, where energy storage and carbon capture and utilization (CCU) technologies play essential roles. To this end, considering the bifunctional calcium-looping (CaL) as high-density thermochemical energy storage (TCES) and high-efficient CC technology, this paper innovatively proposes a zero-carbon-emission solar-coal hybrid system for power and methanol coproduction. The concentrating solar thermal (CST) in the system is used to provide the heat required for regeneration of the adsorbent for the CC in coal-fired power plant (CFPP). The CaL-CST-CFPP is coupled with photovoltaic (PV)-driven electrolysis and green methanol production technologies to realize the resource utilization of CO₂. A steam cycle and a reaction process have been designed to efficiently recover three high-grade heat sources in the carbonator side and calciner side. The system is evaluated by comprehensive analyses based on energy, exergy, economy and environment (4E). In terms of energy and exergy, the proposed system reaches energy efficiency of 30.1 % and exergy efficiency of 32.9 %, respectively. Meanwhile, the system can operate all-day-round and produce 7461.36 MWh of electricity and 2068.22 t of methanol on daily basis. The largest energy/exergy loss is found 82.2/84.3 % of total in photovoltaic electrolysis (PVE) subsystem during daytime and 71.1/49.8 % of total in CFP subsystem during nighttime. In terms of economy, the levelized cost of electricity (LCOE) is 0.025 $/kWh, the cost of methanol production is 510.771 $/t, the payback period is 8.223 yr and the profitability of investment is 12.161 %. By comparing with the individual reference systems, the annual power generation and methanol production of the proposed system are 2499555.6 MWh/yr and 692853.7 t/yr, respectively, with increases by 15.0 % and 3.4 %. In terms of environment, the exergoenvironmental impact factor, the exergoenvironmental impact index and the exergy stability factor are 0.671, 2.04 and 0.329, respectively. Meanwhile, the CO₂ emission can be reduced by 100.0 % and the coal consumption can be reduced by 15.5 %. These results reveal that the proposed system has the characteristics of high economy and emission reduction in energy storage, power generation and methanol production, and has great development potential.