A User's Manual for DELSOL3 - prod.sandia.gov - Sandia National ...

c) PreciDitable Water
The precipitable water overhead (in mm) on the Ith calculational day is given
by DH20(I) (IWEATH=l) or H20 (IWEATH=O, 2). This quantity is used only
in the Allen insolation model (INSOL=3).
111.8-4. Sunshape-The image of the extraterrestrial sun is limb darkened; Le.,
the insolation decreases toward the edge. The size and shape of the solar inten-
sity is further modified by the very small angle scattering in the earth’s atmo-
sphere. In general, the size of the solar image increases as the total insolation de-
creases because of increased scattering. The shape of the solar image is important
in its effects on the spillage and flux calculations. The sunshape models available
in DELSOL are set by the choice of parameter NSUN (Namelist BASIC).
a) NSUN = 0, Point Sun
A point sun, while unrealistic, has been useful for debugging the field perfor-
mance calculation and for studying the effects of heliostat size and errors on the
images projected on the receiver.
b) U J N = 1, Limb Darkened Sun
This is one of the simpler models for a limb darkened sun described by Refer-
ence 3:
So (1.0 - 0.5138(r/R)4) (rR)
where r 1= angle subtended between the center of the sun to
some point toward the edge (R)
The user specifies the intensity vs. angle in a circularly symmetric sunshape.
There are NSUNPT pairs of values of intensity, SUNI, vs. angle from the center
of the sun, SUNR. The angles are in ascending order and the first angle must
be zero (i.e., the center of the sun). mxSUNI(r)dr gives the power from the sun
within a differential circular ring from r to r+dr.
The default in the code is the limb darkened model (NSUN = 1).