Harnessing the ocean for energy has been discussed for years, and now a major utility in the U.S. will purchase some sea power.
Pacific Gas & Electric, the large Northern California utility, has signed a power purchase agreement with Finavera Renewables for 2 megawatts of electricity that will come from a wave farm, which Finavera will build 2.5 miles off the coast near California's Humboldt County.
Ideally, the wave farm will start producing power in 2012. It will offset 245 tons of carbon dioxide annually, and if it succeeds, Finavera will expand the wave farm to 100 megawatts.
"With PG&E behind us, we will be able to go to a bank, if we can show there is no technology risk, to get financing," said Jason Bak, Finavera's CEO, in an interview. The exact location of the wave farm will be determined by the location of onshore power lines and electrical stations.
Finavera makes a device called the Aquabuoy, a buoy connected to a long underwater piston. As the buoy bobs up and down on the waves, it pushes the piston, which pressurizes a chamber filled with seawater. The pressure cranks a turbine and electricity is made.
A full-scale buoy from Finavera will be capable of generating 250 kilowatts, enough for 80 homes. The 2-megawatt field will consist of eight devices. A 100-megawatt array of them could be squeezed into a few square miles on the sea.
Several companies and university laboratories are experimenting with ways to harness tides and waves to produce power. Some small-wave and tidal-power devices exist, but mostly it's an industry in the experimental phase. Unlike wind or sunlight, waves and tides are fairly predictable, a major plus for utilities looking for stable green sources of power.
Sea water is also more than 800 times denser than air at sea level, which means wave farms or tidal turbines can produce quite a bit of power with only a little equipment and real estate.
Ten years from now, the U.S. could produce 10 gigawatts of wave power and 3 gigawatts of tidal power, said Roger Bedard, ocean energy program leader for the Electric Power Research Institute and an admitted optimist on the subject. That's enough for 4.3 million homes (assuming 3 kilowatts a home).
Challenges and costs
Bedard further estimated that there is a potential 2,100 terawatt-hours worth of wave energy off the shores of the U.S. and 250 terawatt-hours of it could be harvested economically. That's about 6 percent of U.S. electrical demand.
The catch? Neptune doesn't play ball. A prototype Finavera put in the ocean off the coast of Oregon . The company was trying to pull the buoy out of the sea when it began taking on water and sank. Finavera will try to recover it in January and determine what went wrong. A valve may have accidentally opened, said Bak.
"The main thing we learned is 'make sure you have a lot of air bags handy,'" he said. "With more air bags, the boat could have towed it to shore."
Verdant Power, which put six tidal turbines in New York's East River earlier this year, found that the strong currents have been shearing the tips of the rotor blades and bending some of the bolts that hold on the blades.
On the bright side, these are likely conquerable problems. The Aquabuoy actually performed well on tests prior to the mishap, Bak said.
Building this equipment, inserting it into place, and then connecting wave and tidal systems to the grid with underwater cables also costs quite a bit. Finavera's long-term goal is to have the Aquabuoys produce power at 5 to 8 cents per kilowatt hour. That's more expensive than coal (3 cents) or natural gas (4 to 5 cents) but less than offshore wind turbines (15 cents) or solar (18 or more cents, depending on the circumstances.)
"We want to be cheaper than offshore wind," he said.
Environmental concerns are also a major issue. Most wave technology can't be seen from shore, but it can get hooked into boat engines and, possibly, disturb marine life. Over the next three years, Finavera will be in contact with groups and organizations that have an interest in the coastline, including crabbers, surfers, and residents, Bak said.