Forty gigawatt-hours per year: This is the European goal for tidal energy by 2050, according to the Green Deal. But currently, installed capacity in Europe barely exceeds 30 megawatts. The problem? Traditional turbines are too expensive, require deep waters, and are complex to maintain. The answer may come from Bavaria, where researchers at the University of Munich have tested a system that seems straight out of a ski resort: underwater kites attached to a continuous cable, similar to a ski lift, which generate energy from ocean currents.
The device is called CableKites It weighs 100 kilos, measures 18 meters and operates with currents of just 0,6 meters per second. In tests on the Isar canal, the kites reached 1,5 m/s, a thousand times more compact than an equivalent wind turbine.
A ski lift that works in reverse
The CableKites system replicates the mechanics of ski lifts, but inverts the energy flow. In traditional ski lifts, motors on the pulleys move the cable that pulls the skiers. Here, the cable, pushed by submerged kites, turns the pulleys where the generators are installed. As Robert Meier-Staude explains, fluid mechanics specialist of theUniversity of Munich,
“Our goal was to test the prototype's functionality. The location near Landshut was ideal: the canal current flows at a constant 0,6 meters per second, comparable to marine conditions.”
Kites aren't just flat surfaces. They're airfoils optimized to maintain stability in the water and convert current into thrust with maximum efficiency. One meter long and 20 centimeters wide in the test version (five times larger in a commercial setup), these devices "fly" underwater as they would in the air. The difference? Water is a thousand times denser than air, allowing an underwater wing to generate the same energy as an air surface a thousand times larger.
Ocean Currents: The Ignored Resource
Ocean currents are the most predictable renewable source we have. A study by Florida Atlantic University has shown that some ocean areas generate power densities exceeding 2.500 watts per square meter, 2,5 times the value of wind power under the best conditions.
Approximately 75 percent of the high-energy density zones cover 490 square kilometers of ocean with levels between 500 and 1.000 watts per square meter.
Yet we continue to ignore them. The installation and maintenance costs of traditional marine turbines remain prohibitive. The structures must resist salt corrosion, organisms that attach to the surfaces, and variable currents. CableKites attempts to solve these problems with a modular and relatively simple configuration. The prototype "underwater ski lift" tested weighed 100 kilograms and was lowered into the canal by crane. A commercial system could be installed in multiple arrays at a significantly lower cost than turbines anchored to the seabed.
The project was born from the collaboration between theUniversity of Munich, Technical University of Munich e enrope GmbH, a ski lift manufacturer based in Wackersberg. Anton and Peter Glasl, the company's founders, developed the basic concept: using cable car technology to capture energy from currents. According to a study published in the Journal of Ocean Engineering and Marine Energy, the German tidal potential in the North Sea is estimated at between 66,6 and 565,8 GWh per year, excluding the most energetic estuaries.
Underwater ski lift: real-world tests and commercial prospects
The Isar Canal near Landshut offered ideal conditions for testing: constant flow, a controlled environment, and accessibility for monitoring. The team spent two years designing, simulating, and building the prototype. The results exceeded expectations. The kites maintained stable alignment in the current, traveling through the water at up to 1,5 meters per second. three times the speed of the flow that was pushing them.
"We describe the movement of underwater kites as flight, since water behaves similarly to air, but is a thousand times denser," explains Meier-Staude. This density allows the kites to be drastically reduced in size. In a full-scale commercial installation, they would still be five times larger (about five meters), but they would still be infinitesimal compared to wind turbines of equal power.
The future of ocean currents in Europe
Europe aims to install, as mentioned, tidal power plants generating 40 gigawatt-hours per year by 2050, as foreseen by the European Green DealCableKites technology could contribute to this goal if it moves beyond the prototype stage and reaches commercialization. Michael Garrett, co-author of the study, emphasizes that "by learning how our signals travel through space, we gain valuable insights into how to secure the communications spectrum and design future systems."
Other countries need to follow Germany's example. France, with its historic La Rance power plant (operating since 1966), the United Kingdom with the MeyGen project in Scotland, and South Korea with the 254 MW Sihwa Lake plant: these are pioneers who have demonstrated technical feasibility. Economic scalability is lacking. If installation and maintenance costs decrease, marine currents could become a cornerstone of Europe's energy transition.
"The prototype test demonstrated that a tidal power plant using cable car technology is technically feasible," Meier-Staude concludes. The next phase involves pilot plants offshore, where currents are stronger and energy production is scalable. Underwater ski lifts.
Until yesterday it seemed like a joke. Today it's engineering applied to ocean currents.
