N13A-T022 TITLE: Development of Next-Generation Composite Flywheel Design for Shock and Vibration Tolerant, High Density Rotating Energy Storage

TECHNOLOGY AREAS: Ground/Sea Vehicles

OBJECTIVE: To explore and develop a next generation composite material designs for high density flywheel energy storage, suitable for high shock and vibration Navy/USMC applications.

DESCRIPTION: High rotational speed energy storage systems (high speed flywheels) have the potential for substantial energy density improvements as compared to common designs utilizing common materials (high performance metals). A key aspect of this improvement in density is the ability to have sufficient strength to withstand the rotational forces associated with operating to the 100k RPM level or above. Composites are ideal materials for this application because of their ability to provide the strength required for large amounts of energy stored at high speeds, while maintaining light weight. Reduced mass of spinning components aides in overall design by reducing the requirements on bearing assemblies, as well as reduced inertial loading stresses at high rotational speeds. High strength is needed to achieve maximum rotational speed. Therefore, advanced composite rotors enable the storage of greater amounts of energy on a per unit weight or volume basis, in comparison with other materials. Additionally, there is the potential for greater levels of safety due to burst and fracture characteristics of composite materials versus metallic wheels and chemical batteries.

To improve performance envelope and increase capabilities of rotating storage, the U.S. Navy is interested in developing and characterizing high strength advanced composite wheel designs, scalable for various storage applications (power and energy applications) at elevated temperatures (temperature range of 40-140F). This materials approach must have lightweight, resilient characteristics which can be supported across a wide temperature range and over a long period of lifetime. When designed with a bearing system and support equipment ruggedized for shipboard application, the ability to retain safety and performance over long duration at speeds in the ca. 100K RPM range is essential to transitioning higher density rotating storage shipboard. Other properties of interest include the thermal and mechanical fatigue under service loading, and benign failure modes which include shredding and breakup into small pieces that will not have sufficient force to damage other equipment. These materials should enable both retrofit to existing flywheel and bearing designs, as well as new approaches to more compact and improved designs.

The Navy will only fund proposals that are innovative address R&D and involve technical risk.

Metrics for complete system (including flywheel system, containment and support equipment):
>350W/L
>80Wh/L
>60kW/flywheel assembly
5-50 second full charge time
5-500 second full discharge time

PHASE I: Provide an initial development effort that demonstrates scientific merit and capabilities of the proposed composite materials for application in a modular, high speed rotating storage application. Laboratory scale specimens should be fabricated and characterized thermally and mechanically. These composite material characteristics should be applied to notional flywheel energy storage system designs to determine the benefit and energy density of a notional flywheel system.

PHASE II: Fabricate and characterize prototype composite wheel to support a demonstration flywheel design capable of >60kW output for >10 minutes, with a peak power capability of >120kW for >4 minutes. The system design should account for operation at the upper range of temperature, and provide the capability to last for 60000 hours of online use and support 1000 cycles.

PHASE III: Produce flywheel energy storage system to support shipboard energy storage requirements as well as other applications where chemical batteries are not feasible and/or long shelf life is critical.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Successful development of high strength, next-generation flywheel materials for compact, modular energy storage will have application anywhere that such a requirement is necessary. Examples of locations where reduced mass and size are critical include mobility applications where volume is a major premium, and renewable energy systems, where size-efficient co-location of storage with the main converters have the potential to reduce cost and simplify transient operation. Integration of rotational energy storage is desirable any place where a rotational transfer of power is utilized, as the storage system may be clutched and/or geared in to provide additional power transfer to or from the system as needed.

REFERENCES:
1. Portnov, G. G., and Bakis, C. E.; "Estimation of Limit Strains in Disk-Type Flywheels Made of a Compliant Elastomeric Matrix Composite Undergoing Radial Creep," Mechanics of Composite Materials, 36:87-94 (2000).

2. Kelsall, D.R.; "Pulsed power provision by high speed composite flywheel," Pulsed Power 2000 (Digest No. 2000/053), IEEE Symposium, pp.16/1-16/5, 2000.

3. Hebner, R.; Beno, J.; Walls, A.; "Flywheel batteries come around again," Spectrum, IEEE , vol. 39, no. 4, pp. 46-51, Apr 2002