Self-Sustaining Wave Energy Capture for Persistent Autonomous Ocean-Going Systems

Unmanned surface and undersea vehicles need regular recharging, and since they often operate far from human contact, their charging systems require a reliable, self-sustaining power source. The Office of Naval Research (ONR) believes the ideal power source will be a wave energy capture device (WECD). WECDs capture kinetic and potential energy generated by the movement of ocean waves on or near the surface of open water. The desired WECD must be portable, specifically, designed as a set of components that can each be carried by one or two people who must be able to quickly assemble and disassemble those components. Components designed for one-person carry should weigh no more than 14 kg with largest dimension no greater than 1.9 m, while components designed for two-person carry should weigh no more than 45.4 kg with largest dimension no greater than 2.3 m. The WECD must be able to be relocated to areas of very different depths, including full ocean depth so the WECD’s design cannot require placement or anchoring on the sea floor. And since the WECD may need to deploy near the shore, its design must allow it to function in waters as shallow as 100 meters. Ocean weather conditions can be challenging. The WECD should function reliably at Sea State 6 or less (very rough seas, with wave heights of 4 to 6 meters), and it should be able to survive conditions up to Sea State 8 (very high seas, with wave heights of 9 to 14 meters). ONR assumes the WECD will be tethered to some device at or near the surface of the water. That tethered system may be an autonomous vehicle in loiter mode, and since loitering involves continuous vehicle movement, the WECD should operate reliably while in motion, and its design should leverage such motion to increase energy capture. The WECD should produce a minimum of 20 kilowatt-hours (kWh) per day, but more is highly desirable. ONR believes 100+ kWh per day is achievable. Even in calm seas, the ideal WECD should produce sufficient electricity to charge a 2-kWh battery in 6 hours or less. Vehicle movement may be considered when ensuring this minimum level of power generation. The desired WECD may be needed in areas where human assembly is impractical. Thus, the deliverables must include a prototype device capable of deploying the assembled WECD from the deck of a medium or large autonomous surface vessel. Like the WECD itself, the deployment device (DD) should function reliably in challenging weather conditions: Sea State 4 or less (moderate seas with wave heights of 1.25 to 2.5 meters). Once deployed, very little of the WECD itself should be visible at the surface of the water. The WECD should minimize any increase in the visibility of the vehicle it is tethered to. This includes surface and airborne observation, both optically and by radar. Acoustic noise generated by the WECD should either be minimized or disguised to seem environmental or biological. Cost for the WECD and associated DD should be minimized. ONR expects that under certain environmental conditions or mission requirements, WECDs may not be recoverable. At full-rate production, the ideal price will allow for multiple units per million dollars. Under normal operating conditions, including Sea States of 6 or less, the expected operational duration of the deployed WECD should be at least one month, with three months or more expected if Sea State 4 or less is maintained.