Massive wind turbines to generate renewable energy are appearing all over the world, but they can be expensive or impossible to install in remote locations and deep waters. A growing complement is the use of huge, specialized kites at an altitude of up to a half-mile, where wind currents are the strongest. Proponents say the solution is ideal for isolated locations. In Mauritius, an island nation off the coast of Africa, a gigantic sail is programmed to make figure-eights overhead and create enough electricity to power up to 50 homes. The International Energy Association predicts wind energy to increase 11-fold by 2050, with wind and solar combined accounting for 70 percent of the Earth’s electricity demands.

In some places, land for wind farms is scarce, and it takes roughly 71 acres to generate a megawatt compared to 12 acres for a fossil fuel plant. Cristina Archer, director of the Center for Research in Wind at the University of Delaware, notes, “The first farms are in the best spots, and the best spots are limited.” Airborne options range from soft wings to complex, rigid designs that carry turbines and generators on board and shuttle electricity down a tether. Wind farms hosting hundreds of kites could be tethered to barges in deep water far offshore.