The group fo Shanhui Fan published a paper in Nature, “Passive radiative cooling below ambient air temperature under direct sunlight.” I demonstrates how a nanostructured surface and shift the wavelength of radiant emission into a band where the atmosphere is transparent, greatly increasing the thermal gradient and cooling potential by radiating to the sky. They were able to cool the surface to 4.9 degrees C below the ambient air temperature in sunlit conditions.

Nature paper:

http://www.nature.com/nature/journal/v515/n7528/full/nature13883.html

Media article:

http://www.sciencedaily.com/releases/2014/11/141126133821.htm