Energy Storage is a key Issue for Long Endurance autonomous underwater vehicles. Mission duration, speed through the water and sensor and payload capabilities are constrained by the energy available, which in turn is governed by the characteristics of the energy source or sources and the mass and volumn that the vehicle designer can devote to the energy system. Tensioned against these technical issues are those of cost, operational life, ease of use, maintainability, safety, securty and continuity of supply of the items forming the energy system. This paper focuses on primary and secondary electrochemical batteries, how existing vehicles have constructed their energy storage systems and seeks to establish whether electrochemical cells alone will be able to provide the necessary energy at an affordable cost for future long endurance AUV’s and the missions being considered.More
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.More
This paper provides a technology assessment for an Unmanned Underwater Vehicle (UUV) fuel cell energy/power system, including design methodology and design concepts. The design concepts are based on the polymer electrolyte membrane fuel cell operating on hydrogen and oxygen. The technology assessment method presented is a holistic approach which combines alternative hydrogen and oxygen storage (and fuel cell system) options to provide the highest specific energy and energy density – within the constraints of the UUV application. Using this method, some surprising combinations appear as the theoretical “winners” for maximum energy storage within the application
constraints of the UUV.
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.More
This paper reviews the status and projected performance of various power system types, including batteries, fuel cells, and hydrocarbon and liquid-metal-fueled heat engines and examines the relationship between power system type and vehicle diameter on achieved range and payload.More
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.More
The efficiency and quietness of fuel cells make them attractive power sources for the autonomous underwater vehicles of the future. However, several technical issues must be addressed before fuel cells can surpass the performance characteristics of batteries, including efficiency, reliability, durability, standby operation and storage, changes to orientation, and high shock loads. Improvements to the storage of the fuel (hydrogen or hydrogen sources) and oxidizer (oxygen) make the biggest impact on the size, weight, and utilization of fuel cell systems. Proton-exchange membrane fuel cells (PEMFCs) are the most attractive fuel cell system and already have been successfully demonstrated for use in Autonomous Underwater Vehicles (AUVs). AUVs of the future may utilize direct methanol fuel cells (DMFCs) or solid-oxide fuel cells (SOFCs) which can use liquid methanol or diesel fuel instead of hydrogen.More