Futurist Ray Kurzweil notes that solar power has been doubling every two years for the past 30 years — as costs have been dropping. He says solar energy is only six doublings — or less than 14 years — away from meeting 100 percent of today’s energy needs. Energy usage will keep increasing, so this is a moving target. But, by Kurzweil’s estimates, inexpensive renewable sources will provide more energy than the world needs in less than 20 years. Even then, we will be using only one part in 10,000 of the sunlight that falls on the Earth.