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INCOMING
SOLAR ENERGY
Each surface
has a default emissivity and solar absorptivity. The solar absorptivity is the
fraction of incoming solar energy that the surface absorbs. The absorptivity can be
calculated by integrating the product of the spectral solar radiance striking the surface
by the spectral emissivity (or 1.0-reflectance) of the surface.
The absorptivity property
determines the amount of incident solar energy absorbed. The magnitude of incident
solar energy is the combination of the following:
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Direct Solar
Irradiance
- Measured by pyrheliometer (W/m^2)
- Short wavelength
- Depends on angle of incidence
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Diffuse Solar
Irradiance
- Not to be confused with thermal skyshine or sky
temperature which is long wavelength
- No direct components
- Measured by a shadow band pyranometer (W/m^2)
with correction for diffuse shaded portion
- Short wavelength
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Reflected
Solar
- Total solar (direct + diffuse) reflected from
the surroundings.
- Measured by downlooking pyranometer (W/m^2)
- Short wavelength
- Depends on orientation
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