To efficiently harness renewable energy from moving water below the surface of oceans and rivers, an ISE professor is applying and evangelizing a new design approach for turbines that can boost their cost efficiency.
Professor James Allison recently began working with three research projects that have secured nearly $9.4 million in funding from the U.S. Department of Energy, and he is helping design new underwater turbines while also creating tools to assist other engineers to do the same.
Beneath the surfaces of oceans, water flowing in currents carries a significant amount of kinetic energy, stemming from the tidal pull of the moon as well as differences in temperature and salinity. In the case of rivers, the Earth’s gravity pulls the water downward and gives it energy as it flows downstream.
Hydrokinetic turbines can be placed underwater to capture some of this kinetic energy and turn it into electricity, but they are not widely deployed and are currently an expensive source of renewable energy.
“Hydrokinetic turbines are at an earlier stage of development — they're not as mature as wind turbines are,” Allison says. “An infusion of support for research into hydrokinetic turbines, this could have a big impact on the levelized cost of energy.”
Hence the goal of the Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E), which has committed $35 million in funding to 11 research projects under the program name SHARKS — Submarine Hydrokinetic And Riverine Kilo-megawatt Systems. As the energy transition toward renewable energy accelerates in response to the significant risks of climate change, SHARKS intends to make hydrokinetic turbines more economically viable.
A common theme across SHARKS projects is an emerging design philosophy known as control co-design. Allison, a pioneer of the philosophy since 2011, says the standard process of designing a device is to design its physical parts first, followed by how it will be controlled. But when using control co-design, the two aspects are designed concurrently, which can lead to a more optimized device than could be conceived under the traditional paradigm.
In the case of hydrokinetic turbines, control co-design would mean designing physical elements, such as the blade shape, and control elements, such as monitoring systems, at the same time.
“In control co-design, we look at lots of decisions simultaneously, so that we can get what’s best for the overall system,” Allison says.
Control co-design is a core part of Allison’s three SHARKS projects, which formally began in mid- to late-2021. He is working with turbine manufacturers Aquantis and Ocean Renewable Power Company to design hydrokinetic turbines and their control systems, with a focus on producing electricity at a low cost.
Allison also plays an advisory role for the National Renewable Energy Laboratory as they develop some of the first open-source software that enables the design, simulation, and optimization of these turbines. Previous control co-design work has often relied on custom code that requires a level of expertise from the engineering team, according to the ISE professor. (Among his research partners for the project is Colorado State University Assistant Professor Daniel Herber, an ISE graduate and a former Ph.D. student of Allison.)
Control co-design has been catching on beyond the SHARKS program. The design approach has also been used in ARPA-E’s $26 million ATLANTIS program, which aims to improve floating offshore wind turbines, using control co-. In one research project, Allison is collaborating with researchers at the University of Texas at Dallas to design a wind turbine with a vertical rotational axis — a departure from the standard horizontal-axis wind turbine, with a design that resembles a large egg beater turned upward.
Others are expressing interest in the benefits of control co-design, according to Allison, such as the improved precision that better-designed devices can provide. The ISE professor has discussed the design approach with semiconductor manufacturers, spacecraft designers, and even an optics control researcher at the Laser Interferometer Gravitational-Wave Observatory (LIGO), which detects ripples in the fabric of spacetime using extremely precise lasers. Allison also gave a presentation on control co-design applications at the NASA Ames Research Center.
“There are people who are interested in just, what are the extremes of performance that we can get out of electromechanical systems or any kind of technology?” Allison says.
They aren’t the only ones who see great potential in control co-design. In a September 2019 article published in the journal Advanced Control for Applications: Engineering and Industrial Systems, ARPA-E Program Director Mario Garcia-Sanz called the design approach “a game changer for the control engineer.”
“It combines the creativity of control-inspired paradigms, the formality of co-optimization techniques and the discovery of co-simulation methods to design the entire system and reach optimal solutions that are not achievable otherwise,” Garcia-Sanz wrote.
Yet there’s a shortage of engineers with expertise in the emerging field of control co-design, according to Allison, which is a “huge challenge” in meeting the demand from research projects and companies.
He’s making efforts to expand the community, such as co-organizing a March 2020 workshop centered on the design approach, which was intended to be hosted at the University of Illinois but was made virtual due to the COVID-19 pandemic. Allison is also in the process of creating educational and training programs to teach the control co-design to both students and practicing engineers, including a possible certificate program at the University of Illinois.
“I hope with some improvements, in both formal coursework and in training, that we can get to a point relatively soon where we can be graduating engineers who have practical control co-design knowledge,” Allison said. “Then the companies will have a lot more people to choose from, in hiring people with this expertise.”