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News 29 Oct 07
Whatever Happened to Wave Energy?
Michael Schirber Special to LiveScience
Editor's Note: This is the first article in an occasional LiveScience series about ideas to ease humanity's impact on the environment.
As anyone who has ever been seasick knows, there's a lot of energy in ocean waves. Many proposals have been made to turn that sloshing motion into useable electricity, but most of these projects are stuck on dry land.
"It's a hard technology to try to develop," said Andrew Parish, chief executive of Wavebob Ltd. "The sea is not the most hospitable environment."
However, recent advances in computer modeling have made it easier to simulate the ocean, and thereby develop designs that can efficiently extract energy from the waves. There are now some 90 different ideas out there, but the vast majority remain on paper, Parish said.
"We are past the technological hurdles," said Carolyn Elefant, CEO of the Ocean Renewable Energy Coalition. "Now the problem is just getting the projects in the water."
Hitting the surf
The ocean surface is nearly always in motion, so wave energy can be produced at a more constant rate than wind or solar energy. It also can be located near where most people live, on the coastline.
A rough estimate of the wave energy potential for the United States is 250 million megawatt-hours a year, or about 6.5 percent of current U.S. electricity capacity.
There are good wave resources along the Pacific coast, Elefant told LiveScience. But regulatory red-tape and a lack of financial incentives are preventing development.
In Europe, where there is more support for renewables, a handful of test projects are currently running, and the first wave farm nears completion off the coast of Portugal. And earlier this month, a small-scale prototype of Parish's Wavebob technology began making electricity off-shore from Galway, Ireland.
Wavebob's buoy-like device is currently not making much electricity: just enough to run lights, cameras and computer controls. But it joins a small group of six or seven companies with working demonstrations.
The Wavebob design involves two free-floating parts: a lighter, donut-shaped body bobs on the surface, while a heavier element rests 100 to 130 feet (30 to 40 meters) below the surface. They are linked by a shaft and their relative motion drives a piston that churns out electricity.
Wavebob's unique feature is that it can be tuned to the particular ocean environment. Sensors measure the size and speed of waves, and Wavebob reacts within milliseconds to keep itself resonating with the up and down motion.
Most other wave technologies are only suited for a specific range of ocean situations, Parish said.
The company's engineers have benefited from numerical modeling of ocean hydrodynamics in designing "the appropriate geometry to resonate with the waves," he said.
A variety of choices
Wavebob belongs to a type of wave technology called single point absorber, but there are several other alternatives.
The Portuguese wave farm is employing three Pelamis machines from Ocean Power Delivery Ltd. These so-called floating attenuator devices look like sea-snakes, each 400 feet (120 meters) long. Bending and flexing of the snake segments works hydraulic pumps that generate roughly 750 kilowatts of electricity. Together, the three Pelamis devices will supply 2,000 homes.
Another possibility is oscillating water columns that funnel water into a chamber with air trapped above. Wave motion forces the air pressure to change, which then drives a turbine.
And lastly, overtopping devices capture the crest of a wave in a pool and then generate electricity, like a hydroelectric dam, as the water falls back to the surface.
Parish believes certain technologies may prove better than others. "But there will not be one device that fits all ocean environments," he said.
Out of the bath
Wavebob engineers will continue to optimize the performance of their test unit. They plan to launch a full-scale prototype in 2009, which they expect will produce about 1.3 megawatts of electric power—roughly the equivalent to a large modern wind turbine.
A recent survey of wave energy by the Carbon Trust in the UK found that the current cost of wave energy is about 45 cents to 50 cents per kilowatt-hour, about 10 times the price of electricity from fossil fuels. But the same survey said this price should fall rapidly once larger projects start to be built.
The wave energy industry therefore considers itself to be the next renewable energy be fully commercialized.
"The big challenge is to get more devices out of the bath tub and into the sea," Parish said.
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