Alternative energy: Sky-high kites aim to tap unused wind power

For a child, the simple act of flying a kite can be exhilarating; running and pulling at the line to send it ever higher into the sky where the winds dance to their own wild tune. Those same winds that captivate young imaginations are also working their magic on a growing body of researchers intent on harvesting what are known as high-altitude winds. At a height of 200 meters (656 feet) and more, winds tend to blow stronger and more steadily than those closer to the ground. These winds are so strong, in fact, that they could be used to generate more electricity than we need and significantly more than wind turbines on land can produce. A doubling of wind speed can theoretically generate up to eight times more power.

Moritz Diehl, who heads the Department of Microsystems Engineering at the University of Freiburg, said harvesting high-altitude winds is one of the “most promising” technologies for generating renewable energy in the future.

“You see all the sky above conventional turbines, and you think all this wind energy is just blowing there and it’s not used,” he said.

Stephan Wrage, CEO of the German wind power company SkySails-Power, wants to change that and make the “largest yet untapped source of renewable energy worldwide” suitable for mass use. And he’s not the only one. For years, engineers, various startups and international companies have been in a race to bring high-altitude winds down to Earth at low cost. Many have failed in their attempts and some have gone bankrupt. But others are on the verge of bringing their flying power plants to the market. One of the first projects to attract attention was launched by the US energy company Altaeros in 2010. Their prototype was a generator attached to a helium balloon — in other words, a wind turbine without a heavy base and tower. Tested in Alaska, it was connected to the ground by a cable. According to the company, it produced energy for about 50 households at an altitude of 600 meters.

Around the same time, the German company SkySails developed a high-altitude kite to pull entire container ships. The idea was to save diesel used to run the engine, by up to 10%.

Although the test with the kite worked, the shipping company went bankrupt and neither the kite nor the helium wind turbine conquered the market. But both prototypes pointed to one thing: harvesting high-altitude winds requires flying power plants.

Enter Google. In 2013, the tech giant bought the US airborne wind energy company Makani for an undisclosed amount, triggering euphoria in the niche sector. Their flying power plant, a device about the size of a small aircraft, climbed to an altitude of around 300 meters where it circled in a continuous and automated loop. The high speeds propelled small wind wheels on the wings, which generated electricity. At the time, Moritz Diehl thought it sounded “crazy” — but it worked. A single flying power plant made enough energy for 300 households, according to Makani. It seemed to be the breakthrough everyone had been waiting for, until a device crashed into the sea during a test mission. Google’s parent company Alphabet subsequently dropped the project, expressing doubts about the economic viability of the flying power-drone.

The end of Makani didn’t spell the end of airborne wind energy. A new wave of startups has kept working on increasingly small devices that use ever less material. Some have pursued Makani’s approach, while others have attached their drone to a rope which tugs at a generator. Still others took the same approach but replaced the drone with a kite.