Environment & Energy

Long-Duration Energy Storage:Resiliency for Military Installations
Jeffrey Marqusee, Dan Olis, Xiangkun Li, and Tucker
Oddleifson
National Renewable Energy Laboratory

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Technical Report
NREL/TP-5C00-87646
October 2023

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Suggested Citation
Marqusee, Jeffrey, Dan Olis, Xiangkun Li, and Tucker Oddleifson. 2023. Long-Duration Energy Storage: Resiliency for Military Installations. Golden, CO: National Renewable Energy Laboratory. NREL/TP-5C00-87646. https://www.nrel.gov/docs/fy24osti/87646.pdf

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Executive Summary

This report provides a quantitative techno-economic analysis of a long-duration energy storage (LDES) technology, when coupled to on-base solar photovoltaics (PV), to meet the U.S. Department of Defense’s (DoD’s) 14-day requirement to sustain critical electric loads during a power outage and significantly reduce an installation’s carbon footprint. The LDES modeled is Antora Energy’s battery energy storage system (BESS). It is currently at a technology readiness level (TRL) of 7 and not ready for full-scale deployment. To support decisions on the value of near-term demonstrations, this analysis looked at the potential value of Antora Energy’s BESS if deployed in the future.

Antora Energy’s BESS stores thermal energy in inexpensive carbon blocks. To charge the battery on a military base, power from the grid or an on-base solar PV will resistively heat the carbon blocks to temperatures up to or exceeding 1,000°C. To discharge energy, the hot blocks are exposed to thermophotovoltaic (TPV) panels that are like traditional solar panels but specifically designed to efficiently use the heat radiated by the blocks. In addition, the BESS can directly dispatch thermal energy. It is worth noting that Antora has also developed a BESS that outputs only heat, which will be commercially deployed at industrial sites starting in 2025. Two versions of the BESS that could dispatch electricity as well as heat were modeled, one that would be available in the mid- term (the “Intermediate” BESS) and one that could be available in the long-term (the “Goal” BESS). The Intermediate BESS’s costs are approximately twice as much as the Goal costs, and the Intermediate TPVs have a reduced conversion efficiency leading to a system-level AC-to-AC round-trip efficiency (RTE) of 38% vs. 48% for the Goal system.

The techno-economic modeling was done using the National Renewable Energy Laboratory’s (NREL’s) REopt® model. REopt was modified to model Antora Energy’s BESS and used in an iterative approach to find cost-effective resilient solutions. To model Antora Energy’s BESS, three key changes to the public version of REopt were required. First, the charging and discharging rates had to be decoupled so that the charging rate was not constrained to equal the discharging rate. Second, the daily loss of stored energy (thermal) needed to be included in the model. Finally, the BESS needed to be modeled like a combined heat and power system that can dispatch both electricity and heat.

NREL selected three installations (Table ES-1) representative of many military installations to assess the costs and benefits of using Antora Energy’s BESS coupled to an on-base PV system to provide energy resilience. They cover three military services and are in different states, with sufficient land to potentially site a large PV system. This analysis used these three installations to illustrate the potential value of LDES, not to design or recommend a solution for these installations. Details of existing energy assets and site-specific constraints were not considered.

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