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Back and forth, back and forth. That's the idea behind WaveRoller. The eponymous 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 fibreglass and steel plates on the sea bed. Waves rolling in push over the plates, which rebound after the wave passes, only to be knocked down by the next wave. The back-and-forth motion of the plates drives a piston and creates hydraulic pressure, which ultimately gets fed to a turbine to generate electricity.
By being completely submerged, WaveRoller's device could help quell some of the NIMBYism that comes with building in coastal areas, CEO Tuomo Hyysalo said in an interview during a break at the Nordic Green conference earlier this week. It also makes the device less prone to being an obstacle for boats. Ideally, the four-metre-high plates will be anchored in water ten to 12 metres 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-metre segmented device that looks like a giant orange sea snake. Others, like the Limpet, are large cement structures anchored to the shore.
A 'staple' in renewable energy
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 commercially sized devices in the 2010-to-2015 time frame.
"The mayor of Peniche is a surfer and he loves it," says WaveRoller's 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 metres and can generate ten to 13 kilowatts of power. Commercial units will likely consist of three plates lined up near each other and would produce around 45 kilowatts, he says. So you'd need about 22 three-plate devices for a megawatt. A single WaveBob, meanwhile, 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; so a few devices planted in a relatively small area can generate as much power as a large wind farm.
Underwater dangers
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," jokes James Ryan, who manages strategic planning and development services for wave power at Ireland's Marine Institute.
Still, maintenance and repairs are going to be one of the big challenges for WaveRoller, Hyysalo acknowledges. The plates could break loose or get frozen in place, for instance.
So how does WaveRoller get its plates down there? "It is like building a bridge," Hyysalo says. The construction area is isolated from the rest of the sea and then drained.
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