Getting in the Water With SHARKS

NREL Earns Four ARPA-E Awards To Make Tidal and Riverine Energy an Affordable Option

May 31, 2022 | By Caitlin McDermott-Murphy | Contact media relations

A group of sharks swimming underwater — Across the United States, underwater turbines—whose blades look a bit like shark fins—could produce energy equivalent to the electricity needed to power every home in all six New England states and New York state combined. But first, these technologies must get hardier and cheaper, and NREL researchers are leading and supporting several award-winning projects to get marine energy to market. *Photo from Jakob Owens, Unsplash*

What do a BladeRunner, RAFT, and kite have in common? They are all SHARKS, and they are getting in the water.

Despite the predatory nature of the animals that are their namesake, these electronic SHARKS only swim to serve. They are all designed to do one critical thing: turn tides and river currents into an affordable source of renewable energy. In the United States, these rushing waters carry about 94 terawatt-hours of energy per year. That is enough to power about 9 million homes, roughly the size of the six New England states and New York state combined.

There is just one problem. These riverine technologies—which often look like mini submerged wind turbines—are still too expensive for widespread adoption. That is why we need SHARKS, which stands for the tongue-twisting Submarine Hydrokinetic And Riverine Kilo-megawatt Systems, a high-risk, high-reward research program funded by the U.S. Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E). ARPA-E is the energy equivalent of DARPA, whose funding created the internet, among other life-altering inventions. Through SHARKS, ARPA-E, along with partners like the National Renewable Energy Laboratory (NREL), could make it possible for marine energy devices to power up in rivers across the country and play a valuable role in combating the climate change crisis.

“Tides and river currents could be a huge boost to the U.S. power grid,” said Michael Lawson, the marine energy group manager of NREL’s water power research and development program and a lead researcher on one of the SHARKS projects NREL is supporting. “The resources are abundant and renewable. But compared to other energy generating sources, the technologies are still expensive. SHARKS is helping fix that.”

The SHARKS program funds efforts to make underwater turbines an affordable, reliable, and substantial source of clean energy for U.S. communities, especially remote villages that often rely on expensive shipments of diesel fuel to power their lives. Of the 11 SHARKS grants ARPA-E awarded in November 2020, NREL is leading one and supporting three others.

One Code To Rule Them All

Trial and error—or, as researchers like to call it, iterative design—is a fine way to invent new technology. But is it practical to construct, say, a building just to learn what might go wrong? Not really. It is far quicker and cheaper to hone the design before construction. So why do so many marine energy developers still build and plunge prototypes into rivers to see how well they work?

Simple: No software could holistically assess novel marine energy technologies—until now.

“Our tool allows simultaneous design of all of a device’s different components,” said Nick Johnson, a mechanical engineer at NREL and principal investigator on the laboratory’s SHARKS award. “This type of software doesn't exist in the industry.”

Johnson and his team of NREL engineers are developing the first open-source software to combine all those design steps into one streamlined—and therefore faster and more cost-effective—approach. The tool is a form of something called control co-design, a technical term for blending technology design, optimization, and control (the ability to manipulate the device’s energy production from afar).

Say, for example, a developer wants to build their underwater turbines with bigger blades. Users can plug in that information to learn how that change might impact their technology’s cost, energy output, and robustness. “We can do very quick, lower-fidelity simulations on the order of seconds,” Johnson said. “Or we can use higher-fidelity simulations in a matter of minutes to hours—this project provides the tools to do both.”

Because underwater turbines share similarities with wind turbines, the team is relying on NREL’s veteran wind energy code, OpenFAST, as a foundation. Both wind and water are fluids, but water is a thousand times denser than air. So, Johnson and his team are adapting OpenFAST to account for these physical differences and provide marine energy developers with accurate simulations of how different designs would perform in the real world. “Our tool will help accelerate the design of more innovative, cost-competitive marine energy technologies to get them closer to where wind energy and solar power are today,” said NREL’s Thanh Toan Tran, a mechanical engineer who is working on the project along with Hannah Ross, a postdoctoral researcher at NREL.

“There’s been really big growth in the wind energy industry,” Ross added. “A lot of that can be attributed to the availability of modeling tools. Marine energy is where wind energy was 30 or 40 years ago. And higher-risk research and development programs, like SHARKS, are crucial for us to advance the industry towards commercialization.”

Getting Three More SHARKS Ready To Swim

While Johnson leads his SHARKS award—and external SHARKS teams prepare their BladeRunner, RAFT, and kite for the water—three other NREL research teams are supporting industry and university award winners to achieve their cost and operational goals. These teams are:

Elena Baca and Ritu Treisa Philip and University of Washington: Baca and Philip, both research engineers at NREL, are developing custom code for the University of Washington to analyze the power and cost performance of the team’s tidal turbine arrays (a set of turbines installed together, like a wind farm). Because individual tidal turbines can affect how water flows around them, different arrangements can increase or decrease the energy production of downstream turbines. The University of Washington research team aims to identify the optimal design for these tidal energy farms while Baca and Philip analyze whether specific technology designs could make that farm cost-effective.
Michael Lawson and Littoral Power: With Lawson’s support, Littoral Power will analyze their turbine design, which includes a buoyant underwater vehicle tethered to the riverbed by one mooring. Attached to the other side of the vehicle is a turbine, which rides on currents like a kite on wind. Because this design reduces the stress on the mooring line, it could reduce the overall operational and maintenance costs and, therefore, the cost of energy it produces.
Scott Hughes and Aquantis: NREL’s Hughes, a mechanical engineer, is assisting Aquantis to assess their Tidal Power Tug, an especially low-weight tidal energy design, which is more cost effective, too. Looking more like an imperial spacecraft in a galaxy far, far away than an electricity-generating device, the design’s vertical and horizontal turbine blades are well suited to survive even aggressively turbulent seas.

All three SHARKS projects could benefit from the control co-design tool NREL researchers are currently developing.

“Without this tool there’s been a big gap for the marine energy industry,” Ross said. “There are bits and pieces of tools scattered around the world, but ours is the first to combine them all and close that gap. I’m personally very excited to see the next generation technologies our code helps build.”

Partner with NREL! The laboratory's teams are committed to providing flexible support for the budding marine energy industry to help technologies achieve commercial success.

NREL is also seeking marine energy industry input! Want to help NREL researchers hone their control co-design code? Get in touch today.