Riding the power of undersea waves

MENLO PARK, Calif.--Back and forth, back and forth. That's the idea behind WaveRoller.

The company, based in Espoo, Finland, says it has devised a way to generate electricity from waves without buoys or other floating devices, the mainstay of other wave power companies.

Instead, the company wants to plant oscillating fiberglass/steel plates on the sea bed. Waves rolling in push over the plates, which rebound after the wave passes to only be knocked down by another wave. The back-and-forth motion of the plates drives a piston and creates hydraulic pressure. The pressure ultimately gets fed to a turbine to generate electricity.

By being completely submerged, WaveRoller's device could help quell some of the NIMBY-ism that comes with building in coastal areas, CEO Tuomo Hyysalo said in an interview during a break at the Nordic Green conference here earlier this week. It also makes the device less prone to being an obstacle for boats. Ideally, the 4-meter-high plates will be anchored in water 10 meters to 12 meters deep.

Some wave power devices--such as the buoys being developed by WaveBob and Finavera Renewables--are fairly unobtrusive. They sit far offshore and can be lit so boats can navigate around them. Others, however, are quite large. The Pelamis from Pelamis Wave Power, for example, is a 120-meter segmented device that looks like a giant orange sea snake. Others, like the Limpet, are large cement structures anchored to the shore.

WaveRoller installed a second prototype off the coast of Peniche, Portugal, earlier this year and this summer will begin to collect data on how well the plates perform. If all goes well, the company hopes to start producing systems commercially and helping power providers build multi-megawatt power plants in five to seven years or so. (Other wave companies are similarly aiming at producing power with commercial-size devices in the 2010 to 2015 time frame.)

"The mayor of Peniche is a surfer and he loves it," said Hyysalo, adding that surfers are often some of the biggest opponents. They fear that wave power devices will sap the strength of waves.

The plate in the latest prototype measures 4x4 meters and can generate 10 kilowatts to 13 kilowatts of power. Commercial units will likely consist of three plates lined up near each other and produce around 45 kilowatts, he said. Thus, you'd need about 22 three-plate devices for a megawatt. A single WaveBob can produce more than a megawatt of power.

Wave power, at least according to its advocates, could become a staple in renewable energy over the next two decades. Waves are far more predictable than wind and solar conditions. Satellites can track wave trains out at sea and give utilities and power providers advance estimates of how much power they can hope to generate from the sea. Water is 800 times denser than air; thus, a few devices planted in a relatively small area can generate as much power as a large wind farm.

Ireland, Scotland, Hawaii, Oregon, and some South Pacific nations are already, or are preparing, wave energy tests.

But there is the catch. Wave power devices have to sit in some of the harshest environments on the planet and function fairly flawlessly to be economical. Right now, virtually all wave power systems are prototypes.

Being completely submerged could potentially become an advantage in this department. Historically, marine engineers have built structures so that they sit above the wave line, like oil derricks, or beneath it. Building devices that are supposed to live on the surface of waves "goes against every instinct of mankind," joked James Ryan, who manages strategic planning and development services for wave power at Ireland's Marine Institute, in a recent interview.

Still, maintenance and repairs are going to be one of the big challenges for WaveRoller, Hyysalo acknowledged. Could these plates break loose or get frozen in place? Sure.

So how does WaveRoller get its plates down there? The construction area is isolated from the rest of the sea and then drained.

"It is like building a bridge," Hyysalo said.