A window into the future of wave energy

The award helps bring the cost-effective, productive and robust wave power design closer to commercialization and widespread use

In 1974, Stephen Salter, a professor at the University of Edinburgh, sent his “ducks” to Scottish seas, launching the world’s first major wave energy project. But the heavy swells and ocean waves proved too strong for its house-sized floating generators. Like Pelamis’ later model P-750 and Aquamarine’s Oysters, they succumbed to the power they were meant to harness.

“We have to ask ourselves,” said Krish Thiagarajan Sharman, endowed chair in renewable energy at the University of Massachusetts Amherst, “why have we been working on this for so long? Why don’t we have commercial-scale grid-ready wave energy systems in the world? »

The answer: wave energy technology must be cheaper, produce more energy, and brave the force of the ocean better and longer.

Today, the Marine Energy Team at the National Renewable Energy Laboratory (NREL) has designed a system that could meet all three needs. The oscillating wave energy converter with variable geometry creates windows for the passage of waves so that the wave energy devices do not bear the full force of their power. The design could also be more cost effective, productive and resilient.

Two years ago, this concept won a competitive award from the U.S. Department of Energy’s Technology Commercialization Fund (TCF), a nearly $30 million funding opportunity designed to help promising, high-impact energy technologies to move towards marketing. With essential support from the TCF award, Nathan Tom, Mechanical Engineer at NREL, partnered with Sharman. Together, they took the wave energy converter system from theory to practice, bringing the potential solution closer to commercialization and bringing wave energy closer to large-scale deployment.

This small prototype (seen from above) can open the slats to allow waves to pass through rather than crash into the device. This wave escape hatch protects the tech from hard impacts, which can help it last longer in the ocean. Photo by Jacob Davis, University of Massachusetts Amherst

“All wave energy devices need a way to survive for several years in the ocean,” Sharman said. “It’s a way.”

Wave power may not match global wind and solar power generation anytime soon, but it remains a critical source of clean, renewable energy. Waves are more predictable and reliable than solar or wind power, and they could power hard-to-reach places, like coastal communities and remote islands, which currently rely on expensive, carbon-intensive diesel imports. . Wave-powered devices could also power deep-sea fishing, marine research, or military operations that need to reach deeper waters. In the United States, waves carry the equivalent of about 80% of the country’s energy needs. Not all of this energy can be practically harnessed, but industry could have enough to facilitate the country’s transition to 100% clean energy.

Today, wave energy is not yet very powerful. Today’s designs fail for the same reason Salter’s ducks struggled; the ocean contains power stronger than any wind, and although some recent wave energy inventions have steel hulls, this armor is too heavy and expensive to make the technology viable. Today, approximately 35-50% of wave energy costs are spent on structural improvements.

“Our systems are just too heavy,” Tom said. “To withstand really extreme loads, orders of magnitude higher than when the device is operating and producing power, they are built with too much steel. We have to start thinking outside the box.

NREL’s design is certainly outside the steel box. To source electricity from the waves, the more economical, lighter and more robust wave energy converter uses a rectangular vane that swings back and forth on a bottom hinge, like a distaff in the wind . The oscillating vane is a common design feature for wave energy devices. But this one is much more adaptable. As the waves change from productive to destructive, the device operator can open one or more horizontal flaps, creating spaces for this violent energy to escape.

This extra level of control not only protects the device, but can also help the converter produce more power. When the sea changes, remote operators can switch each flap to extract as much energy as possible.

With funding from the TCF Prize, Tom and Sharman built their first small-scale prototype for testing in the university’s wave tank. The project team included Jacob Davis, a graduate student at the University of Massachusetts Amherst, and postdoctoral researcher Jessica Nguyen (Nguyen started out as a graduate student). Cole Burge and Salman Husain, undergraduate and graduate research interns from the National Renewable Energy Laboratory, also contributed.

“The Variable Geometry Project had a huge influence on my career trajectory,” Davis said. “In fact, this experience has fueled my passion so much that the focus of my current Ph.D. work is entirely on measuring and understanding ocean surface waves. I look forward to a career spent applying this knowledge to a wide range of ocean-related challenges, including the role of waves in marine energy conversion, weather and climate.

Together, the team checked their theoretical models against experimental data and found, to their relief, that the models accurately predicted the performance of the device. It was a promising start. But the design has to go through much more iterative stages before it can hit the ocean.

With this wave tank at the University of Massachusetts Amherst, the researchers verified that their prototype oscillating variable-geometry surge wave energy converter performed as well as predicted by their theoretical models. Photo by Jacob Davis, University of Massachusetts Amherst

“I could quickly design something to go in the water,” Tom said, “but what if it only put out one watt? cable from sea to land – which is not cheap.

This “big move”, said Tom, which comes with high expense and high risk, makes potential wave energy industry partners reluctant to invest in even very promising designs, like their geometry prototype. variable. Many tend to wait for concepts to prove successful in low-risk environments, like digital models and wave tanks.

But this progressive work also requires funding, which is why the TCF Awards are a vital bridge between theory and the market. “We want to develop patented technology far enough for the industry to think, ‘OK, that’s a good idea. It’s something I want to try and incorporate into my design,” Tom said. “That’s when we’ll transfer it to the industry. And for that, the TCF award is super helpful.

The prize also allowed the team to test another innovative aspect of their design: a raised foundation. Often, oscillating surge wave energy conversion devices are attached to the seabed where swirling debris and sand can interfere with operation. Raised from the seabed on a column, the device can avoid these obstacles and access more places between the sand and the surface or in deeper water. Since surface waters are often more energetic, devices that can reach these areas could produce more energy.

Together, the raised foundation and variable geometry could help wave-powered devices adapt better to their ocean environment than previous designs, including Salter’s Ducks (although those early forays were key to advancing the industry).

“We don’t see the waves as a force to be reckoned with,” Sharman said, “but to be used to harness energy. It’s a very holistic and symbiotic approach to managing our interaction with the ocean.

Learn more about the Variable Geometry Marine Energy Project and NREL’s hydropower research. Subscribe to the NREL Water Power newsletter for the latest marine energy news from NREL

Article published with the kind permission of the National Renewable Energy Laboratory. By Caitlin McDermott-Murphy.


 

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