Wave glider concept

By continuously harvesting energy from the environment, Wave Gliders are able to travel long distances, hold station, and monitor vast areas without ever needing to refuel. A unique two-part architecture and wing system directly converts wave motion into thrust, and solar panels provide electricity for sensor payloads. This means that Wave Gliders can travel to a distant area, collect data, and return for maintenance without ever requiring a ship to leave port.

http://liquidr.com/technology/wave-glider-concept