
352 Principles of Sustainable Energy Systems
© 2008 Taylor & Francis Group, LLC
7.1.1 Selective Surfaces
Two types of special surfaces of great importance in solar collector systems are selective
and reecting surfaces. Selective surfaces combine a high absorptance for solar radiation
with a low emittance for the temperature range in which the surface emits radiation. This
combination of surface characteristics is possible because 98% of the energy in incoming
solar radiation is contained within wavelengths below 3 μm, whereas 99% of the radiation
emitted by black or gray surfaces at 400 K is at wavelengths longer than 3μm. The dotted
line in ...