There are countless ways to manufacture solar panels, but there's only one metric that counts: how the cost of solar power compares with that of electricity from fossil fuels. Until energy from the sun can beat energy from coal at the marketplace, solar will remain a niche player, adorning the rooftops of those who care more for their green reputation than for their bottom lines. Enter Nanosolar, a San Jose-based start-up that manufactures thin-film solar panels. Unlike the bulky silicon panels that dominate the solar market, Nanosolar thin-film technology is light and extremely cheap to make. The key is the manufacturing process: while silicon panels need to be baked in batches, Nanosolar's thin-film panels roll off the assembly line, as if from a printing press.