Angularly selective microstructured surface for tuning seasonal sunlight interaction.

In the temperate latitudes, high-reflectivity exterior surfaces save energy spent on ventilation and cooling during summer, but cost energy on heating in winter. Angularly selective surfaces that adjust their reflectivities by sun position allow beneficial effects in both seasons - high reflectivity in summer and high absorption in winter. Here we show how a planar microstructured surface can produce such an angularly selective behavior and estimate its energy efficiency under direct solar irradiance at 35° N.