Geological Thermal Energy Storage Using Solar Thermal and Carnot Batteries: Techno-Economic Analysis: Preprint

Joshua McTigue, Guangdong Zhu, Dayo Akindipe, Daniel Wendt

Research output: Contribution to conferencePaper


Energy storage is increasingly necessary as Variable Renewable Energy (VRE) technologies are deployed. Seasonal energy storage can shift energy generation from the summer to the winter, but these technologies must have extremely large energy capacities and low costs. Geological Thermal energy storage (GeoTES) is proposed as a solution for long-term energy storage. Excess thermal energy can be stored in permeable reservoirs such as aquifers and depleted hydrocarbon reservoirs for several months. In this article, we describe a techno-economic model that has been developed to evaluate GeoTES systems. The models are developed by combining the output of specialist models which enables the performance and cost of both the subsurface and surface systems to be captured. Off-design models are developed so that the performance can be evaluated at each hour of the year. GeoTES can be charged with two different energy sources: (1) concentrating solar thermal and (2) renewable electricity using heat pumps (henceforth known as a "Carnot Battery"). The stored thermal energy can be used to generate electricity and - uniquely - also directly produce heat that can be used by industrial processes. Furthermore, Carnot-Battery-GeoTES can also be used to form a cold storage reservoir. Preliminary results that quantify the technical and economic performance of these two GeoTES systems are presented.
Original languageAmerican English
Number of pages18
StatePublished - 2023
EventGeothermal Rising Conference - Reno, Nevada
Duration: 1 Oct 20234 Oct 2023


ConferenceGeothermal Rising Conference
CityReno, Nevada

Bibliographical note

See NREL/CP-5700-88749 for paper as published in proceedings

NREL Publication Number

  • NREL/CP-5700-87000


  • carnot battery
  • reservoir thermal energy storage
  • solar thermal
  • thermal energy storage


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