Back in 2007, Google announced that it would be putting hundreds of millions of dollars into a “strategic initiative to develop electricity from renewable energy sources that will be cheaper than electricity produced from coal.”

This included eSolar and Makani Power. News is out today that Google has now acquired the latter. Brad Stone at BusinessWeek writes:

Last February, Astro Teller, the director of Google’s (GOOG) secretive research lab, Google X, went to seek approval from Chief Executive Officer Larry Page for an unlikely acquisition. Teller was proposing that Google buy Makani Power, a startup that develops wind turbines mounted on unmanned, fixed-wing aircraft tethered to the ground like a kite. The startup, Teller told Page, was seeing promising results, and, he added proudly, its prototypes had survived all recent tests intact.

Page approved Google X’s acquisition of Makani, which was being completed for an undisclosed amount at press time. He also had a demand. “He said we could have the budget and the people to go do this,” Teller says, “but that we had to make sure to crash at least five of the devices in the near future.”

According to TechCrunch, Google invested $10 million in Makani Power in 2006 and another $5 million in 2008. Frederic Lardinois shares a statement from Teller:

Creating clean energy is one of the most pressing issues facing the world, and Google for years has been interested in helping to solve this problem. Makani Power’s technology has opened the door to a radical new approach to wind energy. They’ve turned a technology that today involves hundreds of tons of steel and precious open space into a problem that can be solved with really intelligent software. We’re looking forward to bringing them into Google[x].

Makani Power has the following statement up on its site:

We are happy to announce that Makani Power is being acquired by Google. This formalizes a long and productive relationship between our two companies, and will provide Makani with the resources to accelerate our work to make wind energy cost competitive with fossil fuels. The timing couldn’t be better, as we completed the first ever autonomous all-modes flight with our Wing 7 prototype last week. Makani could not have reached this point without the support of the US Department of Energy’s ARPA-E program and the hard work of our talented team, past and present. We look forward to working with our new colleagues at Google[x] to make airborne wind a cost-effective reality.

Earlier this year, Google put $200 million into a wind farm in Texas.