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2. Enter a value for Diffuse Solar Irradiation, which is the amount of energy per unit area in W/m2
due to diffuse solar irradiation. This value may depend on the time of year, the clearness of the sky,
and also on ground reflectivity. Make your selection in the drop-down list next to Diffuse Solar
Irradiation and either enter a constant value, have the value computed from the solar calculator,
or specify it using a user-defined function. For transient simulations, you have the additional
option of specifying a time-dependent piecewise-linear and polynomial profile for diffuse solar
irradiation.

3. If you are using the Solar Ray Tracing solar load model, then you will need to enter a value for
Spectral Fraction. The spectral fraction is the fraction of incident solar radiation in the visible part
of the solar radiation spectrum. The spectral fraction is not used for DO irradiation since the DO
implementation is intended only for a single band.

Spectral Fraction =

where V is the visible incident solar radiation, and V + IR is the total incident solar radiation (visible
plus infrared).
4. Use the solar calculator to compute solar beam direction and irradiation.
(a) Click Solar Calculator... in the Radiation Model dialog box to open the Solar Calculator
dialog box

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