Design and optimization of a solar distributed energy system based on a power-methanol-power path

Methanol-based energy storage technology shows significant promise for large-scale, long-term energy storage due to its high energy density and low storage cost. However, improving round-trip efficiency through effective system integration is challenging due to the multi-stage energy conversion processes involved. To this end, a novel solar distributed energy system is proposed, which directly utilizes crude methanol and methanol reformate gas. The crude methanol solution produced by the methanol synthesis unit is stored directly without undergoing methanol rectification, and is used as feedstock for the methanol reforming unit. The hydrogen-rich gas from the methanol reforming unit is supplied directly to the high-temperature fuel cell without hydrogen purification. Waste heat from both the methanol synthesis unit and the fuel cell is recovered to drive an organic Rankine cycle for power generation. The comprehensive evaluation of the distributed energy system is conducted through case study analysis and multi-objective optimization algorithms. The results indicate that the proposed system is capable of achieving seasonal energy storage, with a round-trip efficiency of 27.53 %, representing a 24.67 % improvement under the design conditions. Under optimal configuration and dispatch strategies, the system achieves a levelized cost of electricity of 0.2078 $/kWh, a carbon emission factor of 0.0429 kg/kWh, and a solar curtailment rate of 0.82 % in the Beijing region. In comparison, the corresponding performance metrics in the Guangzhou region are 0.2383 $/kWh, 0.0714 kg/kWh and 1.07 %, respectively.