August 15, 2007 4:00 AM PDT

FAQ: Energy on the high seas

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It sounds like a can't-miss proposition: harness the power of the ocean to generate clean, affordable, renewable electricity.

Then there is the reality: staggering construction costs, unpredictable weather conditions, environmental dangers, uncertain outcomes and omnipresent skepticism. Still, several researchers and start-up companies say they have devised systems that will be capable of generating power with waves and tides, or other means related to the ocean. Here is rundown of some of the facts, figures and ideas behind sea power.

Why the sea?
Water is more than 800 times denser than air at sea level. Thus, even slow-moving waves or tides can generate far more electricity than wind turbines could even if the wind blew at 110 miles per hour. Facilities thus require less real estate. Ocean power also remains far more predictable than other alternative energy sources. Solar and wind power vary with the weather. Waves are essentially a form of solar power too and thus will also vary: the sun causes wind, and the wind generates waves. Waves, however, can be tracked from far offshore, allowing computer models to predict electrical output several days in advance.

Tidal power is even more predictable because tides are created by the gravitational pull of the moon.

"With a computer you can produce a timetable for decades. Unlike wind or solar, you can figure out how many megawatts you can sell," said Peter Fraenkel, technical director of Marine Current Turbines. "It is not something that will change the world, but it could save a lot of fossil fuel."

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Where is the best place to situate wave or tidal power plants?
The U.S. Pacific Coast, the Chilean coast and Atlantic Europe are good locations, but so are Alaska, Hawaii and the equator. Tidal power is more site-specific, but could work in most of the same areas. A start-up, Verdant Power, this year inserted the first of six prototype turbines in New York's East River. It's a cost/benefit trade-off, but you'll likely be able to see a lot of these facilities from shore. Waves begin to dissipate energy when the water gets less than 200 meters deep. At 20 meters in depth, a wave might have only one third of the energy it had in deep water, according to a 2006 report from Michael Robinson of the National Renewable Energy Laboratory (NREL). Putting wave harvesting systems farther offshore, however, means that you need a longer cable to connect the harvesting system to the power grid.

How much potential power is out there?
Ten years from now, the U.S. could produce 10 gigawatts of wave power and 3 gigawatts of tidal power, says 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). 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. Tidal, river and stream power could replace another 3 percent. Bedard said he doesn't know which of these ideas will succeed. "There is no magic bullet," he said. "We as a country ought to look at harnessing power from waves and tides. We need all of the alternatives we can get."

OK, sounds good. So what's the cost?
A lot. Estimates range from $4,000 to $15,000 a kilowatt, before rebates, according to NREL, or 9 cents to 11 cents per kilowatt-hour with rebates and incentives. Putting solar panels on a home costs roughly $10,000 a kilowatt before benefits ($30,000 divided by 3). Solar panels, however, are almost risk-free and require almost no maintenance.

What are some of the main approaches?
Buoys: Finavera Renewables and AWS Ocean Energy have created wave power systems that rely on buoys that act as hydraulic pumps. Waves push the buoys down, which drives a turbine. When the wave passes, the buoy returns to its normal spot, only to be pushed again by the next wave.

Finavera's buoys will stick more than 6 feet out of the water and descend more than 70 feet below the surface. AWS' are completely submerged. The hydraulic fluid inside Finavera's buoy is seawater while AWS' Archimedes Water Swing relies on air. A full-scale buoy from Finavera will be capable of generating 250 kilowatts, enough for 80 homes. A 100-megawatt array of them could be squeezed into two to three square miles, said Myke Clark, vice president of policy for Finavera. "It is a lot smaller footprint than offshore wind (turbines)," Clark said. "Our long-term goal is to get to 5 cents a kilowatt-hour, but a whole bunch of things have to happen to get to that point."

The company is almost done installing a half-size prototype off the coast of Oregon and hopes to erect four of the 250-kilowatt devices off the Washington coast by 2009. "Alaska is very interested," Clark added. AWS, meanwhile, will install a 250-kilowatt prototype off the Orkneys in Scotland in 2008 and build a field with 500-kilowatt devices in the U.K. by the third quarter of 2009. By 2013, it hopes to have a 100-device field. The design of the coming devices from AWS were influenced by a pilot study the company kicked off in Portugal in 2004.

Sea snake: Ocean Power Delivery is testing the Pelamis, a device 120 meters (about 395 feet) that looks like a segmented snake. When the segments bob up and down, buoys attached at their joints generate hydraulic pressure. The company has built a 2.25MW system off Portugal consisting of three 750-kilowatt Pelamis wave-energy converters and is aiming to built 5MW and 3MW systems off the coasts of England and Scotland in the next few years.

The water column: Wavegen, a division of Voith Siemens Hydro Power Generation, is experimenting with the Limpet, an oscillating water column. Think of a large cement tube submerged in the ocean, but not attached to the bottom. Waves come in; water rushes into the tube from below and cranks a turbine. The company last month won a contract to install a Limpet in Mutriku in northern Spain that will produce 250 to 300 kilowatts when opened in late 2008 or 2009. Wavegen has had a prototype running off Scotland since 2000.

CONTINUED: Tides vs. waves…
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7 comments

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We can improve the efficiency of a Solar panel solution by 300%
The answer for our energy needs is right above us. Conservation should always come first but then look to the sun which delivers enough energy in 1 day to power all of the worlds energy requirements for an entire year. This does not mean we suggest everyone put a solar panel on his or her roof. We actually think no one connected to the power grid should install a solar panel on his or her rooftop. Do away with the million solar roofs program. It is shinning a bad light on solar. Our Solar Transfer solution will be released shortly but in the meantime run the numbers yourself and say no to rooftop installation of solar panels. The precious material and panels should be placed in the center of a parabolic dish where the sun shines brighter and longer every day. The answer may be to look toward the Ocean but not in the way described in this article. If you have already installed Photovoltaic Solar Panels look into a Solar Transplant to improve your power gain and help the environment 3 times as much!
Posted by Manhattan2 (329 comments )
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Interesting proposition....
It's clear that you are no fan of what CitizenRE is trying to do to
make PV solar panels on a large portion of the population more
comon place. I'm not sure why you think that anyone 'on the
grid' would cause more problems then they are trying to
remedy???

But perhaps you can expand on your ideas about a parabolic
dish to harness the power of the sun so that we have a better
idea about what you are talking about rather then just teasing us
'future tech.' Perhaps you can supply the curious masses with a
link or two about what you are talking about.

You've tickled my curiosity, but I don't like to be tased without
some additonal information to substantiate a claim.

More info please!
Posted by Jim_Mattos (69 comments )
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Solar Transfer - The Explanation
IT'S ********. Manhattan2 always hog the comment section to BS about this terms so you'll google it and go to their website for who know what reason.
Posted by jsmith2007.lol (8 comments )
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Say no to Centralization
Saying no to individual roof top installations is not the answer. There is no shortage of silicon on this planet. Centralized power production is not the most efficient because look at all the infrastructure required (power grid, maintenance of power lines, etc.) When you install your own power production you are no longer controlled by big energy, and you actually recover your cost. Big energy will gladly produce loads of power for as cheap as they can, then charge you up the wazu for it. Then look at things like storms and outages, not an issue if you produce your own power. Support Free, individual-distributed energy production, not centralized control.
Posted by chash360 (394 comments )
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Not enough energy can be captured on a roof
The fixed angles of rooftops in Northern states are no place for photoviltaic panels. You cannot capture enough power for a low enough cost and you will always need the grid. Fix the grid! Power needs to be produced for the lowest cost with the highest gain and lowest CO2 emissions if we will ever have a true option for the future. Our solution does just that. Federal power generation with individual tax-free panel or mirror ownership. We don't really care how it gets done. We just know we have the final solution! You will always get twice the power capture in Arizona or Nevada than in Maine or Michigan. That doesn?t mean the Maine resident can?t go Solar. That resident simply goes solar at a co-located "United Solar Array". Remember the power does not get pushed across the country only the higher profits for the green investor. The power gets used by someone within 300 miles of the collectors or farther once the grid gets fixed. Economies of scale. Location, Location, Location, plus American ingenuity. Yes, we also feel, Google, Wal-Mart and others that have done rooftop installations have made a bad choice. They may be in the Al Gore reasoning mode of Public Relations importance over science and math!
Posted by Manhattan2 (329 comments )
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