Off-grid coastal communities that rely on weather-dependent solar and expensive diesel to meet their energy needs may soon have a new addition to their power production portfolio: Tidal energy. Researchers are testing a buoyant kite that flies underwater to determine whether it can squeeze enough power from intermittent, often slow-moving tidal currents to provide clean energy to small coastal communities. It’s

The rise and fall of Earth’s tides draws water through straits and channels each day with impeccable predictability, driving currents that can carry significant kinetic energy. And marine energy is power dense: It provides more power per swept area, compared to a similar wind field. “Underwater kites can be smaller because water is so much denser,” says Evan Variano, professor of civil and environmental engineering at UC Berkeley

Hydrodynamic lift causes a wing-shaped kite to “fly” in moving water in a similar manner to a kite in the air on a windy day. These underwater kites can autonomously fly figure-of-eight paths with the help of modern sensors and onboard robotics or electronics, allowing them to swoop across tidal currents much faster than the water itself is moving. Couple that movement to a generator and the system can harvest useful amounts of electricity, even close to slack tide—the tidal cycle’s slowest flows. That’s something other strategies for harvesting power, like a fixed seafloor turbine placed in a channel, can’t do.

Kites are beginning to find their wings. The furthest-along has installed a megawatt-scale demo system that delivers electricity from a sheltered bay to an electrical grid. Others, aiming for kW-scale systems, are starting to show what they can do in real-world settings. They’re measuring efficiency in different conditions and preparing pilot-trials of their gear in remote communities.

Tidal Kite Power Generators

In one kite design, a generator sits at the base of the tether, either on a boat or an anchored mooring. The pull from the kite as the tide moves it extends the tether and spins the generator, producing power. Then, like a giant yo-yo, the generator reels it back in using a fraction of that power, thanks to the much lower force on the kite while it’s in its most streamlined position.

The Manta project from SRI International, a research institute in Menlo Park, Calif., adds a special twist. The Manta kite uses a twisted-string tether rather than a static tether to spin the generator without needing high-ratio gearing. That makes for a less-expensive system that’s simpler to maintain, more compact, and more efficient.

But any underwater kite faces the same fundamental challenge, says Chris Vermillion, a mechanical engineering professor at University of Michigan. “It must be continuously flying. That periodic motion requires substantial control.”

That means that kites require an autopilot that constantly adjusts flight path in response to generator load. It’s an intricate dance: There are six degrees of freedom on the kite itself, and three more on the tether. The kite’s pose in the water is stabilized via a rudder, an elevator, and aileron-like blades that control pitch. The wing’s angle of attack relative to the current is established to achieve a balance between speed and force on the tether. And the kite must maintain speed while the generator’s load changes. “Control algorithms are where rubber meets road,” says Variano.

Manta Kite Tidal Energy Performance

In 2025, Variano and his colleagues tested a model kite system with a 1-meter wingspan. Attached to a boat in the San Francisco Bay, it could indeed spin a small generator rated up to 2 kilowatts, and drew over 100 watts at the bay’s typical peak tidal flow of 1.5 meters per second.“The power we generate depends on the flow we have, and the control algorithm we’re using,” says Variano. The team has now begun testing a pilot-scale system with a 2 m wingspan and a 15 m long tether, which simulations indicate should be capable of generating 1 kW of average power over a full tidal cycle, including flow speeds below 1 meter per second.

Each San Francisco Bay test uses a small fishing vessel, anchored to ensure the only flow the kite experiences is from tidal currents. The researchers place the kite in the water, start the autopilot, and watch the kite sweep back and forth like a wakeboarder. Each sweep takes the kite away from the generator, untwisting the tether. “We see the generator gathering power, pausing, expending a little energy to reload the string, then repeat,” says Variano.

Across hundreds of sweeps, the researchers tracked the power generated during different parts of a tidal cycle. They conducted additional tests while towing the kite to create a steady 1 m/s flow. In July and August, they’ll run longer trials, capturing a full tidal cycle at once. Then, they’ll crunch the numbers to tease out how efficiently Manta generates power.

The team will complete their analysis near the end of 2026. For a sense of the numbers, however, Variano points to Manta’s contract with the U.S. Department of Energy’s hydrokinetic technology program, which stipulates a production of 1 kW at less than US $0.09 per kilowatt-hour. “If we were far off, we wouldn’t still be trying,” he says.

Minesto’s underwater kite carries an onboard turbine that harvests tidal energy for local grids.Minesto

Minesto’s Megawatt Tidal Power Kite

One kilowatt might sound small. The largest kite produced by Minesto, located near Gothenburg, Sweden, has a 12 m wingspan and drives a 1.2 megawatt generator to deliver electricity to the grid in the Faroe Islands in the Atlantic Ocean. Minesto’s design, unlike Manta, carries its generator on the wing itself, and an undersea cable transmits power to shore.

“When you study tidal flows of the world’s oceans, you realise low to medium flows are in abundance,” says Martin Edlund, the CEO of Minesto.

Edlund posits that harvesting energy from a mean peak flow down to 1.5 m/s has economic potential. Minesto has succeeded in that “we’re grid connected and we attract capital,” he adds. “But calling us commercially ‘successful’ is a bit ahead of ourselves.”.

For off-grid homes, however, kilowatt-scale energy meets basic needs. Many remote communities in Alaska rely on diesel generators to supplement wind and solar. The team behind Manta plans to test the system in Alaska’s Alexander Archipelago with the Metlakatla Indian Community, using traditional knowledge they’ve shared of the narrow straits that funnel the tides to create strong flows. “We’re small, portable, and could provide clean power to people in these remote coastlines,” says Variano.

BladeRunner Energy, based in Bend, Ore., is already testing a tethered system in Alaska—but using river currents and a “kite” that’s more akin to a corkscrew than a wing. The 2 m diameter rotor generates 5 kW of power in flows between 1.8 and 2 m/s, as demonstrated at the University of Alaska’s Tanana River hydrokinetic test site. If tests using a new 11-kW generator go well, BladeRunner will ship out to the native village of Napaimute in western Alaska. “We want to integrate with the Napaimute microgrid system and replace 100 percent of the diesel they consume,” says Moriel Arango, the co-Founder and CEO.

Compared to other renewables like wind and solar, tidal energy offers consistency and predictability year-round. But in contrast to those more mature technologies, marine energy (which also includes wave energy systems) is at a much earlier stage.“if you compare underwater kites to other marine technologies, I don’t see them being behind the eight-ball at all.”

But even if the technology still has a ways to go, tidal kites are well-positioned to succeed, according to the University of Michigan’s Vermillion. “If you compare underwater kites to other marine technologies, I don’t see them being behind the eight-ball at all,” he says. “I don’t buy the idea that kites are nascent and high risk.”