Sustainability-oriented design and techno-economic assessment of an iron-water paste system for carbon-free power and long-duration energy storage

We introduce a metal-fuel PFBC concept based on iron combustion coupled to hydrogen reduction—the iron–water paste (IWP) cycle—and, within a streamlined framework, conduct (i) material-balance calculations, (ii) co-sizing of the wind capacity and electrolyser rating required for iron regeneration, and (iii) unified techno-economic comparisons of the levelized cost of electricity (LCOE) and storage (LCOS). In a 1-MW benchmark integrating gas- and steam-turbine machinery with cascade heat recovery, the cycle exhibits high conversion performance. Across the scenarios explored, the LCOE spans 0.134–0.475 USD kWh⁻¹, comparable to a green-hydrogen-fired CCGT (0.389–0.723 USD kWh⁻¹); under favourable conditions—5% iron unrecovered and CAPEX − 30 %—the LCOE falls to 0.134 USD kWh⁻¹, below the green-H₂ CCGT corridor. In storage operation, the LCOS is 0.093–0.439 USD kWh⁻¹, of the same order as reference values for BESS and CAES under aligned assumptions. Sensitivity is dominated, on the generation side, by iron recovery, CAPEX, and wind capacity factor, and, on the storage side, by charging price and round-trip efficiency. We conclude that the IWP concept can be competitive for both power generation and long-duration storage, but its quantitative advantage is highly assumption-sensitive; rigorous control of recovery, capital costs, and price inputs will be decisive for commercial viability.