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 than a 217 mph (350 km/hr) wind, according to MeyGen statistics.
Other Saltire Prize competitors seek to tap the power of tides. ScottishPower Renewables, a division of wind energy giant Iberdrola, is developing (though not yet constructing) a Demonstration Tidal Array in the Scottish Sound of Islay. Ten Andritz Hydro Hammerfest HS1000 turbines will be anchored to the seafloor between the islands of Islay and Jura. The test is preparation for development of a 95 MW tidal energy project at the Ness of Duncansby, on Pentland Firth waters.
West Islay Tidal is also promoting a project, a 0.8-square-mile (2-square-kilometer) tidal stream array in 100 feet (30 meters) of water off the West Islay coast. Here, tides are not only strong but also biodirectional, meaning that the ebb and flow run conveniently (for turbines) almost 180 degrees opposed to one another. West Islay Tidal hopes to see installation begin in 2015 and 30 MW capacity complete by the end of 2016
But for all of ocean power's plans and potential, it also poses great challenges. Systems have to be built to avoid injury to marine mammals and other ocean life. They have to be robust enough to survive the rough weather that is common in places with the potential for high ocean energy. Conflicts can arise between use of the ocean for energy and other activities, such as fishing, shipping, and recreation. And not least are the financial challenges of producing energy at competitive rates, and raising investment dollars for new and relatively unproven technologies.
Like his European counterparts in the field, Sean O'Neill of the OREC believes all this can be overcome with a vision of clean energy that won't run out. He also sees a need to speed development of the technology, which will drive innovations that make it cheaper and better.
"We have polluted the oceans for decades, and here we have a new use," he said, "so there is some fear of the unknown, and we do need to make certain of wave and tidal power's impacts and monitor them.
"If there are any negative 