Gaiam Solar Powered Hat Fan&Acirc; Solar-powered hat fan for keeping cool on hot afternoons Mini photovoltaic solar panel harvests enough energy to power fan Grows more powerful and runs faster as the sun gets brighter Clamps to most hats--stiffer brims and baseball caps are recommended Adjustable mount; measures 2.12 x 2.25 x 2.75 inches (W x H x D)