On May 16, Makani released a YouTube video. A camera pans on a T-shaped airplane, with wings stretching 85 feet holding eight small turbines and a tether connecting it to a tall ground station. The plane swoops into the air. It dips and soars, looping elegantly in circles that mimic a windmill, something it was built to replace.
For more than a decade, engineers have been building this “energy kite” to harness wind power with 90 percent fewer materials than conventional wind turbines. But Makani, one of the oldest green-energy projects at Alphabet Inc.’s X research lab, is struggling to take flight. Support from its parent has waned in recent years, according to multiple people who have worked at and with the company.