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

power and annual energy. Section 111.1 discusses the effect this approximation
might have on calculating design point receiver thermal power during system op-
timization. Essentially, the approximation is good if design point spillage is close
to annual average spillage. However, the shape of the image at design point may
well be different from the annual average, so flux levels at a specific point may be
up to 10% different than calculated during a final performance run.
The cosine, shadowing and blocking, and atmospheric attenuation losses used
in system optirnization are calculated using minor assumptions of the effect of
scaling with tower height and receiver size, as discussed below. Unlike spillage
and flux calculations, these losses are calculated separately for design point and
for annual averages used during the optimization.
DELSOL designs a field for each system during optimization by using the in-
solation value REFSOL and the design point efficiencies as discussed below, and
by adding zones or fractions of zones based on best cost/performance until the
requested design power is reached. Note that total yearly insolation, which is
used for calculating annual energy, is calculated during the initial performance
run dependent on the insolation model chds'en, and the design point insolation as
predicted by that model may be different from REFSOL. For an actual plant, in-
solation at design point will vary due to weather conditions, but if design point
insolatioil is reached (REFSOL) then design point performance predictions will be
valid.
1V.A-I. Cosine-The field points remain at the same relative position in units
of tower height as the tower height is varied. The angles between the sun, helio-
stat, and receiver (Section 1I.A) remain the same, and therefore the cosine is not
a function of the tower height. The very small change in the cosine as the receiver
width from the tower centerline is varied is ignored. Thus, only one design point
and one annual average loss calculation is needed for examining a set of systems
during optimization.
1V.A-2. Shadowing and Blocking-The actual shadow cast by a heliostat in
the same relative field position is independent of the tower height. However, the
displacement of heliostats relative to each other in radial layouts depends on the
ratio of the heliostat dimension to the tower height. Hence, the shadowing and
blocking has a small dependence on the tower height. The code, however, neglects
this effect. For large systems, i.e., heliostat dimension/tower height