N142-116 TITLE: Affordable, Scalable, Ocean Energy Harvesting System

TECHNOLOGY AREAS: Ground/Sea Vehicles, Battlespace

ACQUISITION PROGRAM: PMS 406

OBJECTIVE: Develop and demonstrate at sea an affordable, scalable, energy harvesting device capable of extracting energy from the internal ocean thermal gradients to produce electrical power for naval missions.

DESCRIPTION: The endurance of underwater vehicles and stationary platforms has traditionally been limited by power considerations. Away from the surface, sea floor and coastlines the only renewable energy source in the ocean interior is the thermal energy associated with the small temperature differentials in the water column. Historically, Ocean Thermal Energy Conversion (OTEC) has been limited to large scale, surface-based power plants due primarily to the large amount of supporting structures like working fluids, generators and pipes [1], making their deployment in ocean probes and underwater gliders [2] unfeasible. Recent developments in high performance phase change materials [3] offer one of potentially many approaches to the development of a small footprint OTEC device that can function as the power source [4] for underwater gliders or to replenish the batteries of underwater charging stations. Since both underwater devices operate in the ocean interior, extracting energy from the thermal gradients in the surrounding environment in which they are continuously immersed offers the most convenient route to extending their endurance with minimal mission interruption and manned support. Additionally, since these new thermal engines require minimal supporting structures compared to conventional OTEC, the potential exists to develop large scale underwater energy harvesting systems, as opposed to the conventional floating, land-based or hybrid OTEC systems. These underwater power stations would support all current and future underwater missions with higher power requirements than probes and gliders.

PHASE I: Develop conceptual designs for a scalable energy harvesting system that can operate (1) at 0.25W in a compact form factor for integration into an underwater glider as well as (2) a 2kW underwater power station. The design principles should culminate in identifying the material and engineering requirements needed to be met by the proposed system in both of these modes, and outline any associated technical risks. Supporting modeling and simulation efforts should include performance and efficiency comparisons to state-of-the-art systems and incorporate real world conditions such as varying ocean temperature, salinity, geographical location and seasonal fluctuations. The 0.25W compact form figure should be built and demonstrated in a lab environment. Calculations should be extensible enough to estimate the basic operating requirements of a 2kW power station. Additionally, cost estimates of materials, manufacturing and maintenance of each unit should be produced.

PHASE II: Develop 2nd generation prototype systems from Phase I effort. Initial testing to evaluate actual performance against predicted performance in Phase I should be done under laboratory conditions. Prototype performance should be optimized to meet the specifications for field testing. For the high power stationary system, charging schemes should be tested, which may include docking of underwater gliders.

PHASE III: Integrate and test the small power source as a direct replacement for the battery of a SLOCUM glider and/or an ARGO float. Deployment of the large power source in the deep ocean will be carried out for an extended period to assess average energy production.

Upon successful completion of the Phase II prototype it is expected that the transition sponsor would test the system for an extended period of time in a relevant operational scenario to mature the technology to a TRL 9.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Marine Survey

REFERENCES:
1. Coastal Response Research Center, National Oceanic and Atmospheric Administration, "Technical Readiness of Ocean Thermal Energy Conversion (OTEC)" Report, Nov 3-5, 2009.

2. Wood, Stephen, "Autonomous underwater gliders," Underwater Vehicles, 499-524, 2009.

3. Jack A. Jones, Yi Chao, and Thomas I. Valdez, "Phase Change Material Thermal Power Generator," Jack A. Jones; Yi Chao & Thomas I. Valdez, US patent 7987674, issued 2011-08-02.

4. NASA/Jet Propulsion Laboratory, "NASA Demonstrates Novel Ocean-Powered Underwater Vehicle," Science Daily, http://www.sciencedaily.com/releases/2010/04/100405142152.htm.

KEYWORDS: Ocean Thermal Energy Conversion; Phase Change Materials; Slocum Glider; Argo Float; Autonomous Underwater Gliders; Unmanned Underwater Vehicles; Energy Harvesting

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