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The purpose of this project was to investigate the techno-economic benefits that large scale, stationary energy storage technology could provide to military microgrid installations. Maintaining continuity of electric power supply to serve mission critical loads within military installations is a top priority throughout the Department of Defense. Recent increases in the frequency of utility power outages due to weather related events and the potential for cybersecurity threats have created new challenges to ensuring resilient installation operation. Microgrids, often containing diesel generators (DGs) and advanced battery systems, can allow installations to maintain continuity of service and continue to serve critical loads for long duration outages. To date, lead acid and more recently lithium ion batteries have been included as assets that complement DG operation as opposed to DG replacement assets, primarily because of the high cost and limited energy duration of those commercially available battery technologies. However, recently developed flow battery storage technology is a promising potential alternative to reduce dependence on DGs while still ensuring system reliability. Vanadium Redox Flow (VRF) batteries offer unique differentiators to lead acid and Li-Ion battery technologies such as increased safety, longer rated duration, and longer life. However, the nascency of VRF technology and limited understanding of reliability and operational performance, coupled with high equipment cost, typically limit the opportunities for field deployment. It was the objective of this work to study the VRF technology and characterize its reliability related performance to support a microgrid and the economic value the technology can generate for a site, while identifying limitations or challenges related to the technology that need improvement to foster growth of the technology sector.
The core technical work of this project entailed statistical reliability analysis using Monte Carlo based simulation methods, operational modeling of “value stacking” of energy storage using Ameresco’s Python-based AESOP optimization tool, and assessment of 20-year economic feasibility of flow battery, lithium ion battery, and DG enabled microgrids. Time series and Monte Carlo modeling methods were used to simulate system operation.
The results suggest that there is the potential to replace a redundant DG with a VRF battery while ensuring adequate reliability of the microgrid and lowering the cost of critical load support as compared to a DG microgrid. However, results show that certain economic and market conditions are needed to yield such benefits, and that significant capital and operational cost reductions of VRF battery equipment are needed to offer a better alternative to lithium ion battery technology. Finally, because of key initial assumptions within the scope of this work, it is recommended that further investigation be performed to assess the feasibility of the VRF battery solution while incorporating electric distribution system details and further studying the response time, operating characteristics, and system life considerations of the VRF technology.
Technical analysis and results allowed for determination of appropriate system sizing, estimated implementation cost, expected annual operating and maintenance costs, and annual savings and value of the proposed VRF BESS systems at each site that satisfied the baseline reliability Critical Load Coverage Probability Curve (CLCPC). The metric for acceptable reliability performance was a CLCPC that met or exceeded the ESTCP provided fixed load baseline coverage curve as modeled against the 100% of critical load profile. A 20-year net present value (NPV) approach was used to assess project economics, to determine battery configurations that provided an equal or lower cost of critical load support as compared with the DG only baseline.