http://www.pbs.org/wnet/need-to-know/environment/futurist-ray-kurzweil-isnt-worried-about-climate-change/7389/

Ray sez

But doubling every two years means it’s only eight more doublings before it meets a hundred percent of the world’s energy needs. So that’s 16 years. We will increase our use of electricity during that period, so add another couple of doublings: In 20 years we’ll be meeting all of our energy needs with solar, based on this trend which has already been under way for 20 years.

That's what he claims. He does it based on two mistakes - calling solar an information technology, and switching from looking at exponential growth in util/dollar to exponential growth in installed base.