Unlocking U.S. Renewable Potential: A Deeper Understanding Through an Integrated Techno-Economic and Life-Cycle Assessment of Subsurface Hydrogen and Synthetic Geothermal Storage

Abstract Renewable energy is gaining attention due to the need to lower carbon emissions. However, the fluctuating nature of wind and solar energy strains the electric grid, leading to significant energy losses in several regions in the United States. Although energy supply can be managed through storage technologies, the lack of efficient methods and understanding of their impact has limited their integration into the electric grid. This study explores the potential of storing curtailed renewable energy in major U.S. electric regions: ERCOT, CAISO, MISO, SPP, NYISO, ISO-NE, and PJM, through an integrated techno-economic and life-cycle assessment of two emerging storage technologies: subsurface hydrogen (H2) and synthetic geothermal storage. Using the yearly average of curtailed energy from 2007 to 2023, the total efficiencies, levelized costs and greenhouse gas emissions can be quantified, offering a comprehensive evaluation of their feasibility. Various phases were analyzed including H2 and synthetic geothermal fluid production, processing, storage, and power production. Reservoir simulation model was also utilized to determine the withdrawal efficiencies. The results of this study highlight the potential recovery percentages for subsurface H2 storage and synthetic geothermal storage across major U.S. regions, providing a detailed analysis of their efficiency at varying depths. The study also presents the expected minimal levelized cost, measured in $/MWh, offering a clear assessment of the technical and economic feasibility of each storage option. A comparative evaluation across regions can reveal the extent to which renewable energy could have been stored. Additionally, the anticipated greenhouse gas emissions are assessed, allowing for a thorough comparison of the environmental impacts in different regions, thus providing a holistic view of the technologies’ potential benefits and challenges. This study offers a comparative exploration of the potential for integrating subsurface H2 and synthetic geothermal storage into the U.S. electric grid, evaluating their feasibility from technical, economic, and environmental perspectives across different regions.