Devices that create electricity from wave motion and offshore winds could become sturdier, quieter and easier to test at near-ocean-ready sizes, with four new grants to the University of Michigan.
The new funding from the U.S. Department of Energy totals around $5 million, which will be used to develop:
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Shock absorbers that allow mooring lines to last longer and power sensors that monitor the device
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Curtains of balloons and arrays of metal poles in the seabed that mitigate wildlife-disturbing noise produced by offshore wind turbines
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Combinations of hardware and software—called hardware-in-loop platforms—that will enable laboratory testing of ocean-scale wave energy devices by mimicking the power produced by ocean waves
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Standardized testing and a publicly accessible database of the performance of power takeoffs, the components of wave energy devices that convert motion to power
Researchers at Pacific Northwest National Laboratory, the National Renewable Energy Laboratory, Sandia National Labs, the American Bureau of Shipping and Virginia Tech will also contribute to these projects.
Ocean waves and offshore winds could be a vast energy source. The total available power in ocean waves in the United States is equivalent to nearly 60% of the electricity currently produced in the country. Global offshore wind energy can be 18 times the world's electricity needs.
Despite its potential, marine energy is still not as widely deployed as solar panels and land turbines. One reason the technology lags behind other renewables is because they don't survive rough waters. Waves can be strong enough to break mooring lines and leave wave energy devices lost at sea.
The shock absorbers designed in the first project could ensure that mooring lines don't break or weaken to the point that the attached devices can move in ways that prevent them from efficiently generating electricity. The motion of the shock absorbers will also be used to generate a small amount of electricity to power other electronics on the device, such as sensors that monitor the health of the device.
"It can cost around two million dollars to fix a mooring line that is only 30 to 80 meters deep," said Lei Zuo, the Herbet C. Sadler Collegiate Professor of Engineering and each project's principal investigator. "It's best to create as robust a system as possible."
Another limit to marine energy deployment are its environmental impacts. Some regulators and biologists fear that noisy offshore wind turbines could interfere with marine life by drowning out the sounds they use to communicate and navigate. These concerns will be addressed with the balloon curtains, which prevent sound waves produced by wind turbines from moving through the water column, and the metal poles, which stop them in the seabed.
The final two grants will enable easier and more rapid testing of prototype wave energy converters and their components. Today, engineers have to build smaller scale versions of their prototypes to test them in wave tanks, because testing at full-scales in real ocean environments can be expensive and risky—especially if a large wave breaks a mooring line. But the amount of power produced by wave energy converters scales exponentially with the device's size. As a result, components within the prototype device are exposed to uncharacteristically low amounts of power during smaller scale tests.
"Ideally, we would build and fully test a device that is half or one-third the size of an ocean-scale device before we'd deploy it in the ocean," said Zuo, who is also a professor of naval architecture and marine engineering and mechanical engineering. "For our tests in wave tanks, we are limited to prototypes that are 10 to 20 times smaller than ocean-scale devices, which reduces the power by a factor of 3,000 to 35,000."
That scaling problem can leave engineers less certain that their designs will function as expected and survive in expensive field trials. The hardware-in-loop platforms will enable engineers to comprehensively evaluate how well a variety of different power takeoff systems perform under more realistic levels of wave power before conducting any tests in the real ocean. The data that Zuo's team will create from their testing platforms will also be compiled into a standardized dataset for the research community to benchmark their prototypes against.
Other collaborators include Xiaofan Li, a former research scientist of naval architecture and marine engineering at U-M who is now at the University of Hong Kong, and David Dowling, the ABS Professor of Marine and Offshore Design Performance.