"There is 10,000 times more sunlight than we need to meet 100 percent of our energy needs, he says, and the technology needed for collecting and storing it is about to emerge as the field of solar energy is going to advance exponentially in accordance with Kurzweil's Law of Accelerating Returns. That law yields a doubling of price performance in information technologies every year."
"We also see an exponential progression in the use of solar energy," he said. "It is doubling now every two years. Doubling every two years means multiplying by 1,000 in 20 years. At that rate we'll meet 100 percent of our energy needs in 20 years."
The rest of the speculation here:http://www.samizdata.net/blog/archives/2008/03/is_nanotechnolo.html