The Department of Defense, specifically the Navy, is seeking proposals for the development of a High-Density Energy Storage System (HESS) capable of delivering energy to a medium voltage motor drive. The system must meet specific energy storage requirements, including a minimum capacity of 1.1 megajoules (MJ) and a modular design that allows for scalability, while adhering to military standards for durability and safety. This technology is crucial for enhancing energy efficiency in military applications and has potential commercial uses in vehicle and renewable energy storage markets. Interested parties should prepare to submit their proposals by May 21, 2025, with the opportunity details available on the DOD SBIR/STTR website.

## Description

The Navy requires a +/- 1000 VDC, split bus HESS to deliver energy to a medium voltage motor drive. The system must store at minimum 1.1 megajoule (MJ) (Threshold) of energy, 5.5 MJ (Objective) and have a system capacitance that exceeds 2.3 Farad (F) (Threshold (T)), 11 F (Objective (O)). The energy storage system must be capable of both delivering power to a motor via a three-level neutral point clamped (NPC) inverter and accepting power from regenerative braking of the motor. Energy is supplied to the motor for approximately 0.5 seconds, with regenerative braking occurring over a span of 3-5 seconds. Then, energy is supplied to the motor for approximately 20 seconds, the bus is recharged, and the cycle repeats with variable time delay between cycles.&nbsp;The HESS must be modular, meaning you can add or remove additional HESS units to change overall system capacitance. An individual unit should be no larger than 93in x 45in x 81.5in. Military standards should be referenced for shock (MIL-DTL-901E [Grade A]) [Ref 5], vibration (MIL-STD-167-1A [Type 1]) [Ref 6], electromagnetic interference (MIL-STD-461G) [Ref 4], and environmental factors (MIL-STD-810H) [Ref 3] since the system must be rugged to be viable.&nbsp;The energy storage system must also interface with a charging power supply. Existing charging power supplies are capable of outputting 90 kW to each bus at 30 amperes; however, this likely will not be sufficient to charge a highly energy-dense bus in the time required. Therefore, an alternate charging system design, intermediate power electronics between the existing charging power supply and energy storage system, or a hybrid energy storage approach (e.g., using components with different characteristics to promote fast charging during initial motor start-up and maximum energy capture during regenerative braking) are all acceptable approaches and considered within scope. If a new charging system is proposed, it must accept 440 Volts (V), 3 phase AC power. The bus must be charged in 60 seconds (T) or 10 seconds (O) at start up. The charging system can be contained within the HESS cabinet, or a separate cabinet that should be no larger than 48in x 63in x 38in.&nbsp;The HESS must have a locally operable disconnect switch that can be monitored. &nbsp;The system must be capable of being discharged to 0 V via an existing energy dump (resistor bank), must be maintainable, and must not prohibit maintenance of connected equipment. It must have a means of verifying that discharged components have a voltage value less than +/- 20 VDC.&nbsp;The energy density of the system must surpass the limits of typical capacitors. The volumetric density of the system must be at least 615 kJ/mm^3, and the gravimetric density must be at least at 0.1 Whr/kg. The system must aim to minimize weight and volume. If applicable, a battery management system, or equivalent for alternate technologies, must be incorporated to monitor, control, balance, collect data, facilitate safe use of the system, and extend its life. Mean time between failures (MTBF) of the HESS must be greater than or equal to 27,000 operational hours that can be demonstrated via modeling.&nbsp;Capacitors, as a commonly used method of energy storage, may be limited in energy density and ability to quickly store generated energy. Advances in supercapacitors, ultracapacitors, batteries, hybrid energy storage solutions, and other related technologies associated with high-density energy storage may be relevant. A modular or scalable approach is preferred to promote applicability for additional military and commercial use cases.&nbsp;The proposed technology should also ensure that the prototype device can be:<ol><li>integrated seamlessly in place of, or in addition to, an existing energy storage system with minimal modifications to upstream/downstream power equipment and controls.</li><li>scalable for smaller or larger applications in the long term.</li><li>manufactured at a cost-effective price point at scale.</li><li>maintainable by sailors.</li><li>safe to operate/manage.</li></ol>

## Objective

Develop a high-density energy storage system (HESS) for use with an existing medium voltage motor drive system.

## Phase I

For a Direct to Phase II topic, the Government expects that the small business would have accomplished the following in a Phase I-type effort and developed a concept for a workable prototype or design to address, at a minimum, the basic requirements of the stated objective above. The below actions would be required to satisfy the requirements of Phase I:<ol><li> Developed a conceptual design, workable prototype or scalable solution for a high-density energy storage system (HESS) capable of meeting the requirements outlined in the description. </li><li> Demonstrated that the proposed HESS technology offers a higher energy density and more efficient energy storage capability compared to existing capacitor-based solutions.</li></ol>FEASIBILITY DOCUMENTATION: Offerors interested in participating in Direct to Phase II must include in their response to this topic Phase I feasibility documentation that substantiates the scientific and technical merit and Phase I feasibility described in Phase I above has been met (i.e., the small business must have performed Phase I-type research and development related to the topic NOT solely based on work performed under prior or ongoing federally funded SBIR/STTR work) and describe the potential commercialization applications. The documentation provided must validate that the proposer has completed development of technology as stated in Phase I above.

## Phase II

Develop a subscale prototype HESS. Validate and demonstrate that the proposed HESS technology meets requirements for charging, storage, delivering energy in a medium voltage motor drive system, and receiving energy generated by the motor. Develop plans for how the technology can be scaled to meet full-scale system requirements.Assess the prototype focused on energy storage capacity, energy efficiency, heat dissipation, safety, maintainability, and integration compatibility with other system components. Scalability and cost-effectiveness of the proposed technology will also be explored and evaluated.

## Phase III: Dual Use Applications

Develop a full-scale HESS design and integrate it into the existing medium voltage motor drive system, test the new system, and prepare for acquisition into the corresponding program of record.Energy storage for vehicles and renewable energy storage are potential commercial markets for this technology.

DIRECT TO PHASE II: High-Density Energy Storage System

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