The objectives of this project were to:

  • Combine state-of-the-art convex optimization of microgrid energy storage with a novel, low-cost Zinc/manganese dioxide (ZnMnO2) rechargeable battery for comprehensive microgrid energy storage designs with guaranteed optimality of long-term life-cycle costs;
  • Validate the coverage probability curve, resilience, life-cycle cost, and robustness of the designs and;
  • Propose practical solutions that can be implemented on commercial microgrid control products.

Technology Description

The project deployed holistic microgrid energy storage (CMES) solutions for five Department of Defense (DoD) sites with guaranteed optimality, using convex optimization. Based on real data and microgrid simulation models, the investigators drove analytical models for convex optimization, which addressed a complete scope of microgrid design challenges, such as resiliency, ride-through capability, outage duration, and life-cycle cost. The performance indicators were aggregated into a resilience metric, which was balanced with respect to the life cycle costs. The designs were validated using Siemens grid simulation product PSS®SINCAL. The energy management logic ran on Siemens microgrid controllers (e.g., SICAM), and the solution is to be compliant with DoD cybersecurity standards, such as Risk Management Framework and DoD Information Assurance Certification.

Demonstration Results

The CMES solution enabled the researchers to size and design a storage system that guaranteed 100% of installation critical and ride-through load requirement for all the sites. With the addition of the sized CMES solution, the researchers were able to meet 130% of installation critical and ride-through load requirements for all the sites. Even in situations when no diesel fuel is available, the sized CMES solution was able to meet 10% and 30% of installation critical and ride-through load. For four sites (Naval Air Station [NAS] Corpus Christi, March Air Reserve Base, Holloman Air Force Base, and NAS Patuxent River) the CMES solution generates a storage solution where all reliability requirements are met, and the technology investment cost can be recovered in less than 20 years. Finally, for all five sites, the CMES solution shows that one of the generators can be replaced with the storage system without significant impact on the site’s reliability performance.

Implementation Issues

DoD sites have significant potential for improvements in energy resilience, renewable energy usage, and energy bill reduction. Most of the current microgrid designs are based on ad-hoc simulation, where many optimization opportunities are lost due to the large-scale nature of the problem. The CMES method has been developed and validated over years. The project simplified the complete grid model and applied convex optimization to find the global optimal design for the simplified model. Investigators can then search for the optimal solution close to the optimal solution of the simplified system. With this two-step optimization approach, the project explores a much wider scope than traditional simulation-based optimization methods. Due to the large scale of the DoD sites, the potential saving and improvements in 20 years can be significant.