Silicon already transformed the world once courtesy of the computer chip. But could the chief ingredient of sand be on the verge of delivering another technological revolution, this time in an entirely different industry - solar energy? Justin Rowlatt travels to San Francisco to the headquarters of chip-maker Intel, the home of 'Moore's Law', to ask whether the exponential shrinkage of computer transistors it has delivered is about to hit the buffers.

He also meets the author of another 'law' of exponential change, Dick Swanson, founder of Sunpower, who explains why solar panels just keep on getting cheaper. We discover the solar industry's surprising hippie origins with pioneer John Schaeffer at his Solar Living Center, and the even more surprising support that rooftop solar now receives from the opposite end of the spectrum, in the form of Republican stalwart Barry Goldwater Jr. Show less