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

At the time of the comparisons MIRVAL and HELIOS used different descrip-
tions of the heliostat errors. MIRVAL used a 1.65 mrad error in each compo-
nent of the surface normal (corresponding to the DELSOL variables SIGSX and
SIGSY). HELIOS used a 3.3 mrad (=2x1.65 mrad) error in each component of
the reflected vector (SIGTX and SIGTY). These two error descriptions are not
exactly equivalent whenever the cosine < 1. For the 10 AM case the DELSOL
calculation was done twice: once with the MIRVAL error description and once
with the HELIOS error description.
The final complication in the comparisons is a difference in defining the effect
of the individual loss terms. The cosine, spillage, total power and flux definitions
are identical. However, there is a small difference between DELSOL and the other
two codes in defining the shadowing/blocking and between DELSOL and HELIOS
(but not MIRVAL) in defining attenuation. Comparisons of shadowing/blocking
and attenuation are therefore not as meaningful as comparing the other quanti-
ties.
The comparison of the power production is given in Table VII-2. The com-
parison of the flux distribution along a horizontal line through the aperture ten-
ter is shown in Figures VIEl(a) (10 AM) and VII-l(b) (4 PM). The agreement is
good. There are small differences (approximately 1% or less) in some of the pre-
dictions. These differences are not practically significant since the uncertainties in
the input (e.g., heliostat errors) generally produce larger effects. The differences
result from slightly different assumptions in the models, numerical errors, etc. For
example, the DELSOL flux is symmetrical about the receiver center while the
MIRVAL and HELIOS results show a slight asymmetry. The approximately 1%
difference in the flux profiles results from the fact that in order to speed up the
calculation DELSOL assumes that the mirror panels are canted symmetrically. In
actuality, for canting at a fixed time (off-axis cant), the cant of the heliostat pan-
els is slightly asymmetric because the sun angle is slightly different on each cant
panel. MIRVAL and HELIOS include this small effect and therefore produce the
small asymmetry in the image. The asymmetry would not arise for on-axis cant-
ing schemes.
While the predictions are very close, the running times are very different.
Users will probably find that DELSOL is 10-100 times faster than either MIRVAL
or HELIOS.
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