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Electricity from the Motion of the Ocean

Engineering.com ~ Tom Lombardo ~ September 26, 2015

Carnegie Wave Energy, maker of the CETO5, is moving on to a bigger and hopefully better wave power generator. The CETO6 will generate four times as much electricity as its predecessor, thanks in part to a scaled up design.

The 240 kW CETO5 (shown below) contains an energy grabbing buoy that’s 11 meters in diameter. Its unique design not only generates electricity, it can also desalinate water. CETO5 pumps water offshore, where the pressurized water runs a turbine or feeds a desalinating device. But because it pumps water offshore, it needs to be fairly close to shore to minimize losses.

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Carnegie’s engineers used thirty years of ocean measurements to create a Simulink model of the CETO5.  After hundreds of simulations, they built a full scale prototype, and eventually the finished product. CETO5 is currently undergoing long-term testing as part of the Perth Wave Energy Project off the coast of Australia.

On the outside CETO6 may look like a scaled up version of CETO5, but its design is quite different. CETO6  has a 20 meter buoy, nearly twice the diameter of its older brother, giving it 230% more swept area. Like wind turbines, wave power output is proportional to the swept area of the energy capturing device, so one would expect 2.3 times the power. But Carnegie claims more than four times the power – one megawatt compared to 240 kilowatts. How can this be? Well, as I said, CETO6 is more than just a scaled up CETO5.

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CETO6 has its power generator (the Power Take Off) inside the buoy, reducing cost and simplifying installation. The design also cuts down on fluid power losses, since the water isn’t pumped offshore. The tradeoff, however, is that the CETO6 won’t desalinate water. Maybe the extra electricity will allow customers to desalinate water through other means. Carnegie’s engineers probably determined that one multipurpose device isn’t as good as two specialized devices, so they decided to optimize for electricity production. Still, the reduction in losses doesn’t account for that big of a power difference. Where does that extra power come from? As they say in real estate: location, location, location.

CETO6 is designed to operate farther from shore – 11km, compared to 3km for CETO5 – taking advantage of high power waves in deeper water. As a result, Carnegie engineers expect the CETO6 to generate electricity at half the cost of the CETO5, making it cost-competitive with electricity generated from fossil fuels in many locations.

CETO6 could be an affordable alternative for islands that currently import diesel fuel to run their generators. These islands are at the mercy of diesel fuel costs, shipping costs, and trade agreements. For them, wave power offers an inexpensive, clean, and secure source of electricity. It’s unlikely that ocean waves will power the world, but they might play a role in a few niche markets.

Carnegie scientists recently completed a geophysical study off the coast of western Australia near Garden Island. They will install three CETO6 units beginning in 2016. A ten megawatt project is also planned for Hayle Cornwall in the UK; construction is set to begin in 2018.

Images courtesy of Carnegie Wave Energy

http://www.engineering.com/ElectronicsDesign/ElectronicsDesignArticles/ArticleID/10723/Electricity-from-the-Motion-of-the-Ocean.aspx

 

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