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Ultra High Density Carbon Nanotube (CNT) Based Flywheel Energy Storage for Shipboard Pulse Load Operation


The introduction of advanced weapons systems such as rail guns, lasers, and other future pulse loads to future warships create power and energy demands that exceed what a traditional ship electric plant interface can provide. This creates the problem of satisfying growing demand for with stored energy, while working within the limited space available aboard ship platforms. Flywheel energy storage systems are potentially attractive due to high cycle life capability, tolerance for military environmental conditions, and capability for buffering multiple stochastic loads. This is provided by the capability to support rapid discharge and charge cycles on a continuous basis. However, prior Navy flywheel installations have been “built in”, which do not allow for easy removal and replacement via a hatchable and/or modular installation that is scalable for multi-MW operation. The size and overall design of these flywheel systems are driven by issues such as rotor energy density due to tip speed limitations due to available material strength. Carbon Nanotube (CNT) based macrostructures in the form of conductive fiber and sheets with high strength and resilience provide the potential to improve state of the art flywheel energy storage. For flywheel designs, it is anticipated that CNT based composites can increase the available energy by over 30% as compared to existing state of art composite materials. This results in a potentially thermally, mechanically and dynamically compliant system operating with a tip speed greater than 1000 m/s. Given the infancy of this technology, innovative research is necessary to identify and prove the actual improvements over baseline state of the art composite designs, by applying new means of CNT integration into advanced wheel designs. The U.S. Navy is therefore interested in developing and characterizing the advantages of innovative shipboard flywheel system designs, directed and optimized to the MW scale, which maximize the advantages of CNT material integration. For the purposes of this effort, the below theoretical metrics of the flywheel design will be used as a basis. Continuously online charge-discharge of up to 50% duty cycle (e.g. up to 50% charging, 50% discharging). 26” shipboard hatchable design for easy removal or installation of components. Modular installation and operation capability to multi-MW levels, with relevant bus voltage and power conversion. Operation over the temperature range (40 – 140 F). Provide the capability to last for 60000 hours of online use and support >20000 cycles. The flywheel should be designed such that any the inertial material or other moving parts cannot penetrate into any personnel space under a catastrophic failure. PHASE I: Determine feasibility and develop a conceptual system design for a CNT flywheel energy storage system and provide comparison against alternative existing metals or composite materials. The comparative design should highlight advantages that CNT components provide with respect to size, weight and performance in a shipboard environment. Perform an initial development effort that demonstrates scientific merit and capabilities of the proposed CNT materials for application in a high speed rotating storage application. Laboratory coupon specimens should be fabricated and characterized. PHASE II: Fabricate the prototype CNT based components associated with the kinetic energy storage design developed in Phase I to the highest allowable scale given constraints of budget and schedule. Fully characterize and demonstrate capabilities and limitations of the CNT material based component. Update the kinetic energy storage design developed in Phase I based on results. PHASE III: Based on Phase I and II effort, fabricate full megawatt-scale kinetic energy storage system incorporating CNT materials to support shipboard energy storage system incorporating CNT materials to support shipboard energy storage pulse power requirements through the existing ONR Multifunction Energy Storage FNC.
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