Life cycle assessment of a conventional thermal energy storage system versus an alternative steel slag-based system for concentrating solar power plants

Thermal Energy Storage (TES) plays a crucial role in advancing decarbonisation. Its integration into Concentrated Solar Power (CSP) plants can significantly enhance efficiency and support renewable power generation. The primary commercial TES material, Solar Salt (SS), presents technical challenges and has the highest environmental impact in TES systems. An innovative alternative is Electric Arc Furnace Steel Slag (EAFSS), a steel industry by-product that can be repurposed as TES material. However, the environmental sustainability of EAFSS for TES applications has not been comprehensively studied. This research quantified the environmental impact of a thermocline TES system using EAFSS as a filler material, compared with a conventional SS system. A Life Cycle Assessment, employing mass and economic allocation methods, examined EAFSS environmental burdens across two SS reduction scenarios. A sensitivity analysis of EAFSS costs showed savings exceeding 30 % compared to SS. At the CSP plant level, the ReCiPe method indicated impact reductions of 9–10 % using mass allocation and 22–26 % with economic allocation. Global warming emissions were higher with mass allocation (0.400–0.408 kg CO 2eq /kWh) than with the conventional TES system (0.358 kg CO 2eq /kWh), which may benefit steelmaking industries by attributing a larger share of their emissions to CSP systems. In contrast, economic allocation yielded lower emissions (0.330–0.325 kg CO 2eq /kWh), providing more credit to EAFSS for its valorisation. These findings underscore the potential of EAFSS to enhance CSP sustainability while valorising waste/by-products to generate greener electricity.