NREL: A Living Bridge to Clean Energy

Working as a welder in the oil sands of northern Canada, Bharath often came home with black tar smeared all over his face. “It’s not very pleasant,” said Bharath, who is now a research engineer at the National Renewable Energy Laboratory (NREL). Today, his face is far more likely to be covered in salt, partly because he lives on a boat on the ocean and partly because he now has a job researching technologies that generate renewable energy from waves, currents, and tides.

In the United States, tidal energy has the potential to power up to 21 million homes (about 15% of the country’s total number of houses). But today, the technologies are still in the early stages of development. They are also expensive, which is why Bharath recently partnered with one of the country’s few tidal energy test sites, the University of New Hampshire’s Living Bridge project, where researchers can study a real-world tidal turbine beneath New Hampshire’s Portsmouth Memorial Bridge. Collaborating with the University of New Hampshire team, Bharath and his NREL researchers will perform a crucial job for the project. They will design and build tools to collect the data needed to understand how well this turbine is operating so tidal energy can grow into an affordable clean energy resource for communities across the United States.

“Tides are an awesome renewable energy resource because they’re very predictable,” Bharath said. “To mess up the tidal cycles, you’d have to stop the moon or stop Earth’s rotation.” That predictability makes tidal energy a valuable complement to solar power and wind energy; when the sun sets and winds lag, tides keep on surging.

Tides are also the practical choice to power the University of New Hampshire’s so-called “smart bridge.” Outfitted with sensors that monitor the bridge’s structural health as well as weather, traffic patterns, and the Piscataqua River flowing beneath it, the bridge is a kind of living laboratory to study bridge structures, the latest sensor designs, and renewable energy technologies. The experimental tidal turbine installed in the river not only powers those sensors; it also provides clean energy to raise and lower the bridge, allowing boats to pass through, and even powers a few homes nearby.

“The project was a rare opportunity to both understand these turbines and collect and share data with the wider industry,” Bharath said.

The bridge uses a vertical-axis tidal turbine, which looks like an egg beater and spins in the river’s rushing tides. Because these types of devices are less common—most tidal turbines look like vertical helicopter blades—there is less prior research and data available to understand how they work. And, Bharath said, “It’s way too expensive to build several prototypes of these turbines, throw them in the water, and test them individually.” That would be a bit like building a new kind of space shuttle, propelling it into space, and hoping it survives. Luckily, there’s a better, less risky way to evaluate new ideas: numerical models.

“Developers rely on numerical models for early device development,” Bharath said. But even numerical models—which meld physics and mathematics to estimate how designs are likely to function in the real world—are not perfect. To make their models more accurate, Bharath and the NREL team must compare their numbers to actual experimental data. And getting that experimental data is not easy—especially when working with spinning machines submerged in salt water.

To get that valuable data, Bharath and his team are improving the custom-made Modular Ocean Data Acquisition System, which has been collecting and sharing live data on the device’s performance. With the tidal energy device back in their lab in Colorado, the team is adding sensors to measure how much strain tidal forces put on the blades. Once the device is back in the water, those sensors will wirelessly send data to a larger data collection system on a platform above the surface before transmitting it to the cloud where it is stored for future access.

Because wires can get tangled and salt water can be corrosive, the team built custom components—like slip rings that collect data from the rotating blades—to accommodate these challenges. But until the turbine is reinstalled under Memorial Bridge, they won’t know how their system will perform.

“It’s been a fairly complicated build,” Bharath said, “and definitely a learning experience because we’re trying to do all of this in a cost-effective way while also adhering to NREL’s standards for quality assurance. It’s been a fun and big challenge for our designers.”

Bharath’s goal is to have their system gather data on the tidal turbine for two consecutive weeks (enough time to experience the full range of potential tidal stream velocities). They are also using the opportunity to test how well different glues and protective coatings survive on the underwater blades. “There’s a lot that can be done and needs to be done because there are still so many unknowns out there,” Bharath said. Eventually, this data set will be added to the U.S. Department of Energy’s Marine and Hydrokinetic Data Repository so anyone can access it. The data can also improve current marine energy models, like OpenFAST, and help marine energy developers hone their designs.

“One of the reasons I ended up in renewable energy is because I saw what happens on the oil and gas side and realized, ‘Wow; it’s a dirty job,’” Bharath said. Between working for the oil and gas industry and joining NREL, he pursued a graduate degree in theoretical physics. And while the mysteries of outer space may have offered bigger, more complicated problems to solve, Bharath was discouraged that he would never get to see his research lead to concrete answers on Earth.

With the work he is doing now in tidal energy, Bharath said, “you can find an answer. That’s the key difference in my mind. I think we’ll definitely see some tidal deployments that are generating meaningful energy in the near future.”