Excerpt:

If you've seen a strange object up in the air over Alameda Point and wondered if it might be a bird or plane, here's your answer: It's an airborne wind turbine being developed by Makani Power.

Makani's technology, which looks like a wing, kite or blade, is a compact energy system. Unlike a conventional wind turbine that's fixed to a hub, Makani's turbine is anchored to the ground by a tether.

This means it can fly in large circles and sweep through greater volumes of air than a standard wind turbine, and it's also able to fly at greater heights, where winds are stronger and more consistent. As a result, the company says, the Makani airborne wind turbine delivers about twice the energy of a normal wind turbine.