The Value of In-Reservoir Energy Storage for Flexible Dispatch of Geothermal Power

Geothermal systems making use of advanced drilling and well stimulation techniques have the potential to
provide tens to hundreds of gigawatts of clean electricity generation in the United States by 2050. With
near-zero variable costs, geothermal plants have traditionally been envisioned as providing ‘‘baseload’’ power,
generating at their maximum rated output at all times. However, as variable renewable energy sources (VREs)
see greater deployment in energy markets, baseload power is becoming increasingly less competitive relative to
flexible, dispatchable generation and energy storage. Herein we conduct an analysis of the potential for future
geothermal plants to provide both of these services, taking advantage of the natural properties of confined,
engineered geothermal reservoirs to store energy in the form of accumulated, pressurized geofluid and provide
flexible load-following generation. We develop a linear optimization model based on multi-physics reservoir
simulations that captures the transient pressure and flow behaviors within a confined, engineered geothermal
reservoir. We then optimize the investment decisions and hourly operations of a power plant exploiting such
a reservoir against a set of historical and modeled future electricity price series. We find that operational
flexibility and in-reservoir energy storage can significantly enhance the value of geothermal plants in markets
with high VRE penetration, with energy value improvements of up to 60% relative to conventional baseload
plants operating under identical conditions. Across a range of realistic subsurface and operational conditions,
our modeling demonstrates that confined, engineered geothermal reservoirs can provide large and effectively
free energy storage capacity, with round-trip storage efficiencies comparable to those of leading grid-scale
energy storage technologies. Optimized operational strategies indicate that flexible geothermal plants can
provide both short- and long-duration energy storage, prioritizing output during periods of high electricity
prices. Sensitivity analysis assesses the variation in outcomes across a range of subsurface conditions and cost
scenarios.

Reference for published paper: Ricks, W., Norbeck, J., and Jenkins, J.D., "The value of in-reservoir energy storage for flexible dispatch of geothermal power," Applied Energy, Volume 313, 2022, 118807. https://doi.org/10.1016/j.apenergy.2022.118807