Harnessing the ocean waves for emission-free power seems like a tidy concept, but the ocean is anything but tidy. Waves crash from multiple directions on a seemingly random basis, and converting the kinetic energy into electricity is a frontier of alternative energy research that requires grappling with large unknowns.
But with several utility companies and states, and in one case, the U.S. Navy, investing in wave power, or hydrokinetic energy, may not be too far off in the utility mix. At least two companies hope to reach commercial deployments within the next three to five years.
Off the coast of Orkney, Scotland, is the Oyster, a white- and yellow-flapped cylinder, 40 feet tall and firmly locked into the ocean's bed. With a total of seven moving parts, two of which are pistons, it captures waves as they near the coast. Oyster funnels them into a pipe and carries the power inland to a hydroelectric power generator. The generator has been supplying the United Kingdom's grid with 315 kilowatts of energy at peak power since October.
A farm of up to 100 Oysters could yield 100 megawatts, according to Aquamarine Power, the Scottish company that developed the technology.
"From an environmental perspective, in the sea you have a very simple machine that uses no oil, no chemicals, no electromagnetic radiation," said Martin McAdam, CEO of Aquamarine.
The Oyster provides a tiny fraction of the 250 gigawatts of power that the water is capable of providing, including conventional hydroelectric energy by 2030, according to the United Nations. At least 25 gigawatts of that will come from marine renewables, according to Pike Research, a clean technology market research group. The non-conservative estimate is as much as 200 gigawatts. And 2015 will be the benchmark year to determine which of these estimates will be true.
The field of hydrokinetic power has a number of companies such as Aquamarine, all with unique designs and funded by utility companies, government grants and venture capitalists. If at least 50 percent of these projects come online by 2015, marine power could supply 2.7 gigawatts to the mix, according to Pike Research. A gigawatt is the electrical output of a large nuclear power plant.
'PowerBuoy' joins the Marines
There are six marine renewable technologies currently under development that aim to take advantage of ocean waves, tides, rivers, ocean currents, differences in ocean temperatures with depth, and osmosis.
"The energy landscape is going to be a mix of different energy sources, with an increasing proportion coming from renewables," said Charles Dunleavy, CEO of Ocean Power Technologies, a New Jersey-based research group also developing wave energy. "We aim to be a very big part of this."
The company has been testing its wave-energy device, called the PowerBuoy, in the ocean since 2005. It recently launched another device a mile offshore from the island of Oahu in Hawaii and connected it to the power grid of the U.S. Marine Corps base. It now supplies 40 kilowatts of energy at peak, enough to power about 25 to 30 homes.
"The Navy wants to reduce its reliance on imported fossil fuel; they have a strong need to establish greater energy independence," said Dunleavy.
The buoy captures the energy from right-sized waves (between 3 and 22 feet tall), which drive a hydraulic pump. The pump converts the motion into electricity in the ocean using a generator embedded into its base. A subsea cable transfers the power to the electrical grid. A buoy farm of 30 acres could yield 10 megawatts of energy, enough to supply 8,000 homes, said Dunleavy.
The structures rise 30 feet above water, and extend 115 feet down. They would not be a problem for commercial trawlers, which are farther offshore, or for ship navigation lanes, said Dunleavy. Recreational boaters, however, may have to watch out.
'Oyster' competes with the 'top end of wind'
In comparison with a system such as the Oyster that brings water ashore to power turbines, creating electricity in the ocean is more efficient, said Dunleavy. "You lose a lot of energy to friction," he said.
But Aquamarine's system of having onshore power generation will cut down on maintenance costs, according to McAdam. Operation costs are expected to consume as much as 40 percent of the budget of operating a marine power plant, according to Pike Research.
Ocean Power is already selling its device for individual commercial use and building larger units of 150 kilowatts off the West Coast of the United States and for the utility company Iberdrola's unit in Spain.
It is also developing the first wave power station under the Department of Energy's stimulus program at Reedsport, Ore., according to Dunleavy. The farm, which currently has a 150-kilowatt unit, could grow by nine additional buoys.
And as for price, which is a major concern, Dunleavy said that cost compares with other renewables.
"It is cheaper than solar thermal and photovoltaics, and in the range of biomass," he said. "It is at the top end of wind."
The Oyster is also aiming to position itself as an alternative to wind power for utilities. McAdam said that by 2013, his company hopes to be a competitor to offshore wind installations. And by 2015, he hopes to compete with onshore wind.