Google-parent Alphabet is shutting down a unit devoted to using high-tech kites to tap into wind energy for electricity, the chief of the team said on Tuesday.
Makani became a "moonshot" project in a special Alphabet X lab when the startup was acquired seven years ago.
The unit was turned into an independent business last year to see if it could fly on its own.
"Creating an entirely new kind of wind energy technology means facing business challenges as well as engineering challenges," Makani chief executive Fort Felker said in a post at Medium.
"Despite strong technical progress, the road to commercialization is longer and riskier than hoped, so from today Makani's time at Alphabet is coming to an end."
After becoming an independent business, Makani collaborated with gas giant Shell Oil to demonstrate successful flights of energy-generating kites tethered to a floating platform off the coast of Norway, Felker said.
Propellers attached to the kites get them aloft and then act at turbines for generating electricity, which is sent back down the tether, according to the Makani website.
Shell is exploring ways to continue developing Makani technology, Felker noted.
"This doesn't mean the end of the road for the technology Makani developed, but it does mean that Makani will no longer be an Alphabet company," he said.
The Northern California company was founded by a group of kite-surfers "curious about the potential for kites to unlock wind energy in more places," Felker added.