ion because of their potential to disrupt ocean views. (Related: Cape Wind Deadline: Headwinds for Offshore Turbines.)
The buoys are anchored with a proprietary system to avoid seafloor ecosystem damage, and could even provide some benefits to marine animals by serving as an artificial reef, said Charles F. Dunleavy, chief executive officer of OPT.
In addition to delivering power to the grid, the buoys can power themselves at a remote location and support a flexible suite of sensors and equipment for maritime security and monitoring off the grid.
The U.S. Navy's Littoral Expeditionary Autonomous PowerBuoy (LEAP) program tested a smaller, totally autonomous version of the PowerBuoy with acoustic sensors, communications systems and signal processing. The equipment might be deployed someday as maritime surveillance, protecting sensitive areas or equipment and tracking illegal ship traffic.
Floating Pumps "Surf" on Wave Energy
Aquamarine Power's Oyster is a simple design, just as its makers intended, that basically functions as a wave-powered pump. The floating system features a large, hinged flap anchored in 33 to 50 feet (10 to 15 meters) of water in the near-shore zone, some .3 miles (.5 kilometers) out. The flap moves with wave motion, driving attached pistons that push high-pressure water through an underwater pipeline. That water is funneled to shore, where it powers a standard hydroelectric turbine—the design keeps complicated moving parts out of the ocean and on dry land where they can be more easily maintained.
The current Oyster 800 is has been at sea two and a half years—longer than any other mobile wave energy device. The device's location near the shoreline and its design are both aimed at mitigating one of wave power's top challenges-surviving the sometimes brutal conditions in locations like the Scottish coast.
"Survivability is one thing that we think differentiates Oyster, and it can really stay out there in big storms," said CEO Martin McAdam. "It's designed to spill excess wave energy over the top of the machine in storm conditions, because the machine actually ducks under the water and excess energy cascades across the back of the wave."
Oyster has withstood several storms with waves of 26 feet (8 meters) and more. (See it in action with this video.) Because of its location in shallow (40 to 50 feet, or 12 to 15 meters) water, McAdam said the machine shouldn't encounter waves much above 33 feet (10 meters).
The Oyster system is designed for increased scale, so that pipelines could connect several hundred devices to a single onshore plant producing electricity. The company, also chasing Scotland's Saltire Prize, has permits for a 40MW farm off the Isle of Lewis and plans to begin producing power there within four years.
Underwater Turbines Tap Tidal Power
Waves aren't the ocean's only motion. The gravitational pull of the sun and moon causes sea levels to rise and fall reliably, typically twice a day. This horizontal flow of ocean waters offers a regular and predictable energy source that's being targeted by several companies, including Saltire Prize competitors MeyGen, ScottishPower Renewables, and West Islay Tidal.
In September of last year, MeyGen was given a permit to install Europe's biggest tidal turbine array in part of Pentland Firth, the fast-moving channel between the northeast tip of the Scottish mainland and the island of Stroma (map). In a recent study, engineers from Oxford and Edinburgh Universities estimated that underwater turbines in the larger Firth could produce 43 percent of Scotland's electricity needs—up to 1.9 gigawatts. The MeyGen project would be the first commercial tidal turbine operation in Scotland.
To tap tidal power, MeyGen is testing seafloor-anchored turbines from two different manufacturers, Atlantis Resources Corporation and Andritz Hydro Hammerfest. Unlike their wind-driven counterparts, these would be largely invisible from above and benefit from the fact that seawater is 832 times more dense than air. For this reason, a 5-knot ocean current packs more kinetic energy t