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The total available power in ocean waves in the US, for example, is equivalent to nearly 60% of the electricity currently produced in the country. But practically none of that huge potential has been exploited, and the same is true around the world.
Wave energy devices could offer a solution. Converting peaks and troughs into useful movement, they generate electricity as they bob up and down on the surface.
Widescale deployment – even just testing – of the technologies faces some major challenges, however. The nature of their application means they are exposed to rough waters by default. Strong waves can break mooring lines and leave devices lost at sea.
Research efforts around the world, including at the European Marine Energy Centre (Emec) in Orkney, are attempting to solve associated engineering challenges. Now, a new project at the University of Michigan, funded by $5m from the US Department of Energy, aims to develop several solutions.
These could include shock absorbers to prevent damage to mooring lines, which can lead to movements that prevent efficient generation of 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 health-monitoring sensors.
“It can cost around $2 million to fix a mooring line that is only 30-80m deep,” said principal investigator Professor Lei Zuo. “It's best to create as robust a system as possible.”
The researchers will also develop hardware-in-loop platforms to enable laboratory testing of ocean-scale wave energy devices by mimicking the power produced by ocean waves.
Engineers currently have to build smaller-scale versions of their prototypes to test them in wave tanks, because testing at full-scale in real environments can be expensive and risky – especially if a large wave breaks a mooring line. The amount of power produced by wave energy converters scales exponentially with the device's size however, so prototype components 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 marine and mechanical engineer Professor Zuo. “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 field trials. The hardware-in-loop platforms will enable engineers to evaluate how well a variety of power take-off systems perform under more realistic levels of wave power.
Data from the testing platforms will also be compiled into a standardised dataset, for the research community to benchmark their prototypes against.
A promising individual power source for countries around the world, wave energy could also combine with offshore wind to maximise electricity generation from particular areas. The research, involving teams from Pacific Northwest National Laboratory, the National Renewable Energy Laboratory, Sandia National Labs, the American Bureau of Shipping and Virginia Tech, will also look at key issues with offshore wind.
Some regulators and biologists fear that noisy offshore wind turbines could interfere with marine life by drowning out sounds they use to communicate and navigate. One part of the project will develop ‘balloon curtains’ and arrays of metal poles in the seabed, designed to prevent soundwaves from wind turbines moving through the water.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.