Reversible solid-oxide cell stack based power-to-x-to-power systems: Economic potential evaluated via plant capital-cost target

Electrical energy storage systems are indispensable for the electrical grid with high penetration renewables. Reversible solid-oxide cell stack based power-to-x-to-power systems, which can switch between power generation and power storage, can achieve a high round-trip efficiency and are technology neutral for, e.g., hydrogen, methane, methanol, ammonia and syngas. This paper evaluates, with a systematically decomposition-based optimization method, the economic feasibility of such dual-direction plants to assist wind farms for reliable electricity supply, under various scenarios with 150%/200%/250% wind electricity penetration and strong/ weak interactions with chemical markets. The economic feasibility is represented by Plant CAPEX Target (?/refstack), defined as maximum affordable total plant investment costs divided by the equivalent number of reference stacks (5120 cm2 active cell area). The results show that, with strong interaction with chemical markets, hydrogen pathway is the most economically potential, especially under high wind electricity penetration (200, 250%). Plant CAPEX target of hydrogen pathway reaches 2300 ?/ref-stack, followed by syngas (1900 ?/refstack), while the methane, methanol and ammonia ones are less economically-feasible with targets around 1000 ?/ref-stack. Economic feasibility of hydrogen pathway is less sensitive (above 2000 ?/ref-stack) to hydrogen price when it is below 4 ?/kg. Deploying multiple plants with operation-coordination freedom allows for the reduction of lost wind rate and the enhancement of profit. Plant designs with either high round-trip efficiency or good match with imbalance characteristics are preferred. When the chemicals produced are not sold to markets, syngas and methane pathways are more economically-feasible, with plant CAPEX target within 500?1000 ?/refstack due to affordable onsite fuel storage and high round-trip efficiency.