[Editors] MIT eyes efficient wave power

[Elizabeth Thomson]

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Catch the wave

--MIT researchers eye clean energy possibilities along Portuguese coast
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For Immediate Release
TUESDAY, DEC. 16, 2008

Contact: Elizabeth A. Thomson, MIT News Office
E: thomson at mit.edu, T: 617-258-5402

Graphic Available

CAMBRIDGE, Mass.--MIT researchers are working with Portuguese  
colleagues to design a pilot-scale device that will capture  
significantly more of the energy in ocean waves than existing systems,  
and use it to power an electricity-generating turbine.

Wave energy is a large, widespread renewable resource that is  
environmentally benign and readily scalable. In some locations — the  
northwestern coasts of the United States, the western coast of  
Scotland, and the southern tips of South America, Africa and  
Australia, for example — a wave-absorbing device could theoretically  
generate 100 to 200 megawatts of electricity per kilometer of  
coastline. But designing a wave-capture system that can deal with the  
harsh, corrosive seawater environment, handle hourly, daily and  
seasonal variations in wave intensity, and continue to operate safely  
in stormy weather is difficult.

Chiang Mei, the Ford Professor of Engineering in the Department of  
Civil and Environmental Engineering, has been a believer in wave  
energy since the late 1970s. After the recent oil-price spike, there  
has been renewed interest in harnessing the energy in ocean waves.

To help engineers design such devices, Professor Mei and his  
colleagues developed numerical simulations that can predict wave  
forces on a given device and the motion of the device that will  
result. The simulations guide design decisions that will maximize  
energy capture and provide data to experts looking for efficient ways  
to convert the captured mechanical energy to electrical energy.

One country with a good deal of expertise in wave energy research and  
development is Portugal. For the past three years, Mei has been  
working with Professors Antonio Falcao, Antonio Sarmento, and Luis  
Gato of Insitituto Superior Tecnico, Technical University of Lisbon,  
as they plan a pilot-scale version of a facility called an oscillating  
water column, or OWC. Situated on or near the shore, an OWC consists  
of a chamber with a subsurface opening. As waves come in and out, the  
water level inside the chamber goes up and down. The moving surface of  
the water forces air trapped above it to flow into and out of an  
opening that leads to an electricity-generating turbine. The turbine  
is a design by A.A.Wells in which the blades always rotate in the same  
direction, despite the changing direction of the air stream as the  
waves come in and out.

The Portuguese plan is to integrate the OWC plant into the head of a  
new breakwater at the mouth of the Douro River in Porto, a large city  
in northern Portugal. Ultimately, the installation will include three  
OWCs that together will generate 750 kilowatts — roughly enough to  
power 750 homes. As a bonus, the plant’s absorption of wave energy at  
the breakwater head will calm the waters in the area and reduce local  
erosion.

The challenge is to design a device that resonates and thus operates  
efficiently at a broad spectrum of wave frequencies — and an  
unexpected finding from the MIT analysis provides a means of achieving  
that effect. The key is the compressibility of the air inside the OWC  
chamber. That compressibility cannot be changed, but its impact on the  
elevation of the water can be — simply by changing the size of the OWC  
chamber. The simulations showed that using a large chamber causes  
resonance to occur at a wider range of wavelengths, so more of the  
energy in a given wave can be captured. “We found that we could  
optimize the efficiency of the OWC by making use of the  
compressibility of air — something that is not intuitively obvious,”  
Mei says. “It’s very exciting.”

He is currently working with other graduate students on wave power  
absorbers on coastlines of different geometries and on how to extract  
wave power from an array of many absorbers.

Mei continues to be enthusiastic about wave energy, but he is not  
unrealistic in his expectations. Although costs have been falling in  
recent years, wave energy is unlikely to be commercially viable for a  
long time — perhaps several decades. Nevertheless, Mei is adamant that  
more attention should be given to this renewable source of energy, and  
he would like to see a team of MIT experts in different fields — from  
energy capture and conversion to transmission and distribution —  
working collaboratively toward making large-scale wave energy a reality.

“Given the future of conventional energy sources, we need lots of  
research on all kinds of alternative energy,” he says. “Right now,  
wind energy and solar energy are in the spotlight because they’ve been  
developed for a longer time. With wave energy, the potential is large,  
but the engineering science is relatively young. We need to do more  
research.”

Research on the OWC was supported by the MIT-Portugal Program.

--END--

Written by Nancy Stauffer, MIT Energy Initiative

(This article is adapted from a longer version that appeared in the  
autumn 2008 issue of Energy Futures, the newsletter of the MIT Energy  
Initiative, which is available on the MITEI website at http://web.mit.edu/mitei/ 
  .)



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