| Abstract |
In this study, we investigate the maximum duration over which the Earth Battery, an emerging approach to energy storage that uses sedimentary basin geothermal resources, can time-shift electricity generation. Energy storage technologies, like batteries, are needed to time-shift electricity generated by variable renewable energy technologies (i.e., wind turbines, solar photovoltaics) to when it is demanded. There is increasing evidence that energy storage approaches that can time-shift electricity generation over long durations (i.e., days to weeks) will be needed in addition to technologies like batteries that can time-shift smaller amounts (i.e., minutes or hours) of electricity. Sedimentary basins may be uniquely positioned for long-duration energy storage because they are ubiquitous and also have the physical capacity to store large volumes of fluid. For example, these subsurface formations underlie approximately half of North America. Further, they are also naturally porous and permeable and thus the geothermal energy in these formations can be accessed without the creation of artificial fracture networks that are required for Enhanced Geothermal Systems (EGS) resources. We characterize an integrated model of the Earth Battery system that we developed with data from a realistic case-study in the Minnelusa Aquifer within the Power River Basin (Wyoming, USA) and simulate time-shifting electricity over charge-discharge cycles of varying durations. In Earth Battery systems, electricity is primarily discharged by producing brine from the sedimentary basin, using it to generate electricity, and then storing the cooled brine in a surface holding pond. Later, electricity is used (stored) to power pumps that re-inject the brine into the subsurface, where the electricity is stored in the form of pressure. As a result of this operation, the pressure in the subsurface decreases as the duration of time-shifting increases because more brine is produced before being re-injected. If the pressure decreases too much, the brine will flash in the production well and our results suggest that this pressure depletion is the primary factor constraining the durations over which the Earth Battery can operate. Despite this possibility, we find that our current Earth Battery design, when operated in the Minnelusa Aquifer, can likely time-shift electricity over long durations (up to a couple weeks). |