This project aimed to investigate and advance the state of the art in flow battery energy storage. The purpose of this project was to study the reliability and operational effectiveness of flow battery storage and quantify the extent to which it could reduce reliance on diesel generators (DG) in a military microgrid.

The new technology that is the primary focus for investigation through this work is the Vanadium Redox Flow Battery (VRFB). Fundamentally, VRFBs produce or absorb electrical current by pumping a vanadium-based electrolyte solution through a power stack. Flow batteries differentiate themselves from lithium-ion in that the power (kW) and energy components can be adjusted independently of one another without impacting performance.

The core technical work of this project entailed integration of two modular VRFB units with a single power conversion system into a hardware in the loop test bed at National Laboratory of the Rockies in Golden, Colorado. Once commissioned, a series of microgrid tests were performed, aimed at demonstrating the performance of the VRFB in various islanded and grid-connected scenarios. This enabled investigation of the VRFB solution while incorporating electric distribution system details and further studying the response time, operating characteristics, and system life considerations of the technology.

The VRFB performed well in the following seven test scenarios: black start and photovoltaic (PV) reconnection; grid-forming transition to island; pick up load when diesel generator trips; extended duration outage; solar PV smoothing; frequency regulation to PJM signal; and peak shaving to reduce site kW demand. The results suggested that there was the potential to replace a redundant DG with a VRFB while ensuring adequate reliability of the microgrid.

A Cost Assessment was done as part of the Phase 1 study and is not included in this Phase 2 scope. Rather, Phase 2 was intended to focus on the VRFB’s technical capabilities to provide the performance necessary to support a microgrid application. Further analysis of the technology’s economic cost-effectiveness would be developed in the Phase 3 investigation.

There are several inherent limitations of flow storage relative to lithium-ion energy storage systems that likely will not be eliminated through engineering and product development. One of the drawbacks of VRFB relative to lithium-ion is a lower Round Trip Efficiency (RTE). This metric is often described as the ratio of useable output energy to the input energy. Once the operation of pumps and efficiency of the cell stack is factored in, the RTE of VRFB is about 15% lower than commercially available lithium-ion systems. (Project Completion - 2024)