(569b) Carbon Footprint and Energy Analysis of a Mixed Metal Oxide Thermochemical Energy Storage Technology

Strategies to decarbonize electricity generation and distribution require energy storage technologies that deliver power during periods of downtime in variable renewable energy sources such as wind and solar. Ideally, energy storage technologies should not add significantly to the carbon footprint of the renewable electricity grid. In this study, we determine the carbon footprint and cumulative energy demand for a new thermochemical energy storage technology using environmental life cycle assessment (LCA). The technology is based on abundant mixed metal oxide energy storage material that operates over a 20-year lifetime with periodic renewal of the storage material. This energy storage technology can deliver power over a time that is intermediate in the range between short- and long-duration energy storage. Input data for the operation was derived from industry demonstration trials and engineering calculations. The results indicate that the contribution of the process infrastructure and energy storage material manufacture and recycle contribute 36.2 kg CO₂ eq / MWh-e delivered to the grid, a value on par or lower compared to Li-ion battery and vanadium redox flow battery storage, and much lower than conventional fossil-based power (US coal 1,090: US natural gas 736: US grid 502.6 kg CO₂ eq / MWh-e). Also, the total life cycle GHG emission of delivered electricity to the grid for wind and solar PV energy storage are 65.1 and 164.0 kg CO₂ eq / MWh-e delivered to the grid. Technology performance parameters such as round-trip efficiency and efficiency loss factor affected the LCA results significantly, shining a light on areas for improvement.

One important and relevant way to utilize the LCA results from this study is to incorporate the GHG emissions intensities for electricity storage into predictions of renewable energy system performance. A modeling study was recently conducted on storage requirements for high penetration of wind and solar power in the Midcontinental Independent System Operators (MISO) region of North America (1). Their model predicted that energy storage capacity corresponding to the equivalent of 40 days of the average load energy is required at an optimum mix of 40% solar power and 60% wind power. This represents 11% of average load energy supplied by storage and 89% supplied by the installed optimized renewable solar/wind power. Using LCA results from this study, the GHG intensity of the modeled optimized renewable power mix is (0.4)(54.7) + (0.6)(12.3) = 29.3 kg CO₂ eq/MWh-e. Similarly, energy storage emissions intensity is determined to be (0.4)(164) + (0.6)(65.1) = 104.7 kg CO₂ eq/MWh-e assuming that the optimized renewable power mix is applicable to storage. Combining the optimized renewable power mix with energy storage yields the following result for MISO region system carbon intensity; (0.89)(29.3) + (0.11)(104.7) = 37.6 kg CO₂ eq/MWh-e. This result is a very low carbon and stable renewable grid that is over 90% lower than the current U.S. average grid mix carbon intensity, and very close to zero carbon intensity. This abstract is based on the work of Shonnard et al. (2)

(1) Johlas, H.; Witherby, S.; Doyle, J.R., Storage Requirements for High Grid Penetration of Wind and Solar Power for the MISO Region of North America: A Case Study, Renewable Energy 2020, 146, 1315-1324.

(2) Shonnard, D.R., Zolghadr, A., Kulas, D.G. (2025) Carbon Footprint and Energy Analysis of a Mixed Metal Oxide Thermochemical Energy Storage Technology, ACS Sustainable Chemistry & Engineering, in press, Apr. 2025.