Solar-cell arrays catch more light when they can tilt to follow the Sun's path, but this motion tracking does not have to be driven by power-hungry machinery.
Hongrui Jiang and his colleagues at the University of Wisconsin-Madison mounted a platform of solar cells on top of elastic supporting columns. Each column is coated with films made up of carbon nanotubes embedded in liquid crystal elastomers — rubbery networks composed of ordered polymers. When the nanotubes in the columns nearest the Sun absorb sunlight, they convert the energy to heat, and this changes the orientation of the polymer chains, causing the columns to contract. This contraction tilts the solar-cell platform towards the Sun. As the Sun moves across the sky, different columns contract, changing the platform's tilt to track the Sun's motion.
Adv. Funct. Mater. http://dx.doi.org/10.1002/adfm.201202038 (2012)