AUVAC

UUV FCEPS Technology Assessment and Design Process

The primary goal of this technology assessment is to provide an initial evaluation and technology screening for the application of a Fuel Cell Energy/Power System (FCEPS) to the propulsion of an Unmanned Underwater Vehicle (UUV). The impetus for this technology assessment is the expectation that an FCEPS has the potential to significantly increase the energy storage in an UUV, when compared to other refuelable Air-Independent Propulsion (AIP) energy/power systems, e.g., such as those based on rechargeable (“secondary”) batteries. If increased energy availability is feasible, the FCEPS will enable greater mission duration (range) and/or higher performance capabilities within a given mission. A secondary goal of this report is to propose a design process for an FCEPS within the UUV application.

This executive summary is an overview of the findings in the attached main report body (“UUV FCEPS Technology Assessment and Design Process”) which provides a complete technology assessment and design process report on available UUV FCEPS technology, design methodology, and concepts. The report is limited to the Polymer Electrolyte Membrane (PEM) Fuel Cell (FC) operating on hydrogen and oxygen.

MODELING HYBRID ENERGY SYSTEMS FOR USE IN AUVS

Specifying an energy source for an AUV is usually a compromise between performance and cost. For most vehicles and most missions, high specific energy primary lithium batteries are not a practical option due to cost. One solution that shows promise and affordable cost is to use a hybrid approach that combines low cost secondary batteries with a fuel cell or combustion energy source. Exploring the design space for these more complex energy systems requires suitable tools for modelling and assessment. One such tool is Virtual Test Bed. To build confidence in the tool, its simulations have been assessed against experimental data for 18650 lithium ion cells and a Ballard fuel cell, with encouraging results. Subsequently, a conceptual design for a lithium ion battery and fuel cell hybrid energy source was modelled and the performance of two variants assessed for two different 7-day mission scenarios. In both cases, the hybrid system exhibited a specific energy comparable to primary lithium manganese dioxide batteries, with full account taken for the mass overhead of realistic reactant storage for the fuel cell.

Performance and Cost Considerations for UUV Energy Systems Requiring Limited Development

The performance, cost and operational characteristics of a variety of energy systems for UUVs are analyzed. Types considered include batteries, fuel cells and thermal hybrid systems that are available with limited or no development. System size and weight are estimated for a 26.5-inch diameter vehicle with a 300 nm range and hotel loads of 500 watts and 1500 watts. Initial, operational, and expendable costs are also estimated for the various systems.