The energy-generating potential of solar panels — and a key limitation on their use — is a result of what they’re made of. Panels made of silicon are declining in price such that in some locations they can provide electricity that costs about the same as power from fossil fuels like coal and natural gas. But silicon solar panels are also bulky, rigid, and brittle, so they can’t be used just anywhere. In many parts of the world that don’t have regular electricity, solar panels