Final TCF Report for Earth Battery: Storing Energy with Compressed Air and Heated Brine in Porous Rock
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Cost-effective reductions in greenhouse gas (GHG) emissions are best achieved when all low-carbon energy resources are fully utilized. This includes base-load power: nuclear energy (NE) and fossil energy (FE), integrated with CO2 capture, use, and storage (CCUS), and variable renewable energy (VRE) (wind and solar); but, current CCUS options don’t justify CO2-capture costs and existing energy-storage approaches lack the capacity and storage duration needed to fully utilize all forms of low-carbon energy without curtailment. The Earth Battery is designed to meet these challenges by synergistically integrating conventional- and renewable-energy resources, allowing each to contribute more efficiently to the grid than if operated independently. The Earth Battery stores energy underground as pressure and heat, using compressed air and/or CO2, together with heated brine. These fluids are stored in either saline aquifers used for CO2or natural gas (NG) storage or in oil and gas reservoirs, making deployment possible over much of the U.S. We can provide enormous energy-storage capacity and duration. The main goal of this study was to assess the techno-economic feasibility of the versions of the Earth Battery that use compressed air energy storage (CAES). Current CAES systems use NG turbines and store air in salt caverns, which limits geographic deployment. Conventional CAES wastes much of the heat of air compression, comprising half of the compression energy. Our technology addresses these deficiencies by using permeable sedimentary rock to store air and the heat of compression as heated brine. When electricity is needed, air and hot brine are produced, with hot brine used to pre-heat air before it is fed into the expanders. Key factors affecting round-trip efficiency are (1) pressure loss in the air-storage reservoir, which depends on permeability (> 100 mD being needed for efficient operations) and (2) temperature loss in the hot-brine storage reservoir, which decreases with time as the storage formation heats up. The original scope of this project was to conduct a techno-economic assessment of diurnal storage with the CAES Earth Battery, including (1) Adiabatic CAES, which requires no fossil fuel and (2) NG/CAES, where one or more of the expansion stages are NG fueled. During its assessment, we found NG/CAES, generates excess heat of compression that can be put into long-term (seasonal) storage and be utilized in a combined-cycle fashion with the addition of steam turbines. This resulted in our developing a new Earth Battery technology, which we call the Thermal Earth Battery. We conducted energy-system analyses for the Thermal Earth Battery for various combinations of heat sources: (1) heat of FE combustion, (2) excess heat of compression from NG/CAES, and (3) solar thermal energy (STE). The other Earth Battery class we developed compresses CO2, rather than air; hence, it is called Compressed CO2Energy Storage (CCES). Finally, we developed an improved, more efficient, more versatile version of the Allam cycle, which uses pressurized CO2, and developed various options for integrating renewable energy and energy storage. Our improved Allam-cycle technology minimizes cooling-water consumption, while enabling reliable, dispatchable renewable energy. Although not anticipated in our original scope of work, our Topic 1 project evolved into a highly productive discovery process wherein we developed a portfolio of Earth Battery configuration options and use cases. Our ultimate objective was to evaluate those options and use cases and determine the most optimal first best use options for our Earth Battery technology. That process resulted in identifying seasonal energy storage as a niche where no other energy storage technology could compete with us. As a result, we have identified the Thermal Earth Battery, which uses conventional steam-turbine components, and our improved Allam-cycle integrated with renewable energy and energy storage as the most promising technologies to commercialize in our Topic 2 proposal. Finally, our scope included finding a commercialization team for a Topic 2 continuation of this project, which we have successfully completed.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA)
- DOE Contract Number:
- AC52-07NA27344
- OSTI ID:
- 1490931
- Report Number(s):
- LLNL-TR-763284; 953126
- Country of Publication:
- United States
- Language:
- English
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