Iron-based thermochemical energy storage for power generation: A techno-economic analysis

This thesis investigates the technical and economic feasibility of an iron-based thermochemical energy storage (TCES) system aimed at decarbonizing energy production. The system comprises two main sections: a reduction section, where iron oxides are reduced to metallic iron using hydrogen, produced via renewable-powered electrolysis, as reducing agent, and an oxidation section, where iron is combusted in a retrofitted coal-fired power plant (CFPP) with a net electricity output of 800 MW. The reduction section represents the charging phase of the system, during which renewable electricity is stored as chemical energy in the metallic iron. Conversely, the oxidation section corresponds to the discharging phase, where the stored energy is released through iron combustion. The cycle is completed by returning the iron oxides from the power plant to the reduction facilities for reuse. A thermodynamic model, based on mass and energy balances, was developed for both the reduction and oxidation sections to assess the performance in terms of energy efficiency and solid material and energy flows. The system also integrates long-distance transport, allowing iron to be shipped between reduction and oxidation facilities. Four maritime trade routes between iron exporters (Australia, Saudi Arabia, Morocco) and importers (Japan, Germany) were selected as case studies. Based on the thermodynamic results, an economic analysis was conducted to evaluate the system’s financial viability, considering investment costs, operating costs, and the Levelized Cost Of Electricity (LCOE). The results show that retrofitting CFPPs to operate with iron as fuel is feasible, with the proposed system achieving an efficiency of 44.9%, comparable to conventional CFPPs. To meet the iron fuel demand of the oxidation section, the reduction plant must produce 7.4 Mt/year of iron, consuming 21.1 TWh/year of electricity, with the electrolyzer accounting for the majority of this demand (20.8 TWh/year). The overall cycle efficiency ranges from 28.5% for the shortest transport route (Morocco-Germany) to 26.3% for the longest route (Australia-Germany), aligning with values reported in the literature. Economically, the LCOE varies between 0.37 €/kWhel and 0.4 €/kWhel, depending on the route. The electrolyzer is the most significant cost factor, requiring an investment of 2.8 billion euros for a capacity of 3.5 GW. These findings confirm the technical and economic feasibility of the iron-based energy system and highlight the importance of further research into iron reduction and combustion thermodynamics, improving electrolyzer efficiency, and optimizing transport logistics.