We present an approach that uses the huge fluid and thermal storage capacity of the subsurface, together with geologic carbon dioxide (CO2) storage, to harvest, store, and dispatch energy from subsurface (geothermal) and surface (solar, nuclear, fossil) thermal resources, as well as excess energy on electric grids. Captured CO2 is injected into saline aquifers to store pressure, generate artesian flow of brine, and provide a supplemental working fluid for efficient heat extraction and power conversion. Concentric rings of injection and production wells create a hydraulic mound to store pressure, CO2, and thermal energy. This energy storage can take excess power from the grid and excess and/or waste thermal energy and dispatch that energy when it is demanded, and thus enable higher penetration of variable renewable energy technologies (e.g., wind and solar). CO2 stored in the subsurface functions as a cushion gas to provide enormous pressure storage capacity and displace large quantities of brine, some of which can be treated for a variety of beneficial uses. Geothermal power and energy-storage applications may generate enough revenues to compensate for CO2 capture costs. While our approach can use nitrogen (N2), in addition to CO2, as a supplemental fluid, and store thermal energy, this study focuses on using CO2 for geothermal energy production and grid-scale energy storage. We conduct a techno-economic assessment to determine the levelized cost of electricity using this approach to generate geothermal power. We present a reservoir pressure management strategy that diverts a small portion of the produced brine for beneficial consumptive use to reduce the pumping cost of fluid recirculation, while reducing the risk of seismicity, caprock fracture, and CO2 leakage.
Bibliographical noteFunding Information:
This study was funded by the U.S. Department of Energy (DOE) Geothermal Technologies Office (GTO) under grant DE-FOA-0000336, managed by Elisabet Metcalfe and Sean Porse, and U.S. National Science Foundation (NSF) Sustainable Energy Pathways (SEP) grant NSF-SEP 1230691. Martin Saar thanks the Werner Siemens Foundation for their endowment of the Geothermal Energy and Geofluids Chair at ETH Zurich (ETHZ) and the Gibson endowment for their support of the Hydrogeology and Geofluids Research Group at the University of Minnesota (UMN). Any opinions, findings, conclusions, and/or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF, DOE, UMN, ETHZ, the Werner Siemens Foundation, or the Gibson Foundation. This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under DOE contract DE-AC52-07NA27344.