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

a final performance calculation on the optimized system. This difference will be
most noticeable in flux profiles.
The speed of the Hermite method results from the fact that a severely trun-
cated polynomial (6th order) expansion is an accurate approximation to the flux
density. As discussed in Reference 5, the accuracy of the Hermite method in-
creases as the error sources of heliostat performance and/or their effect on the
flux profile become larger. Specifically, DELSOL becomes more accurate in pre-
dicting the flux and spillage when: (1) the errors increase; (2) the slant range in-
creases; or (3) the size of the heliostat is reduced (either physically or effectively
by focusing or canting).
To calculate the fraction of the flux intercepted by the receiver, Equation
(1II.F-1) must be integrated over the projection of the receiver on the image
plane. The resulting two dimensional integral can be evaluated analytically in one
dimension and numerically, using a 16 point Gaussian quadrature, in the other.
I1I.F-I. More Accurate Images from Canted Heliostats-The normal method
used in DELSOL is to use a single Hermite series to represent the heliostat’s im-
age. When the heliostat to receiver distance is small this can result in a blurring
of the sharp edges of the image. A slower running option which calculates a more
accurate image is available for canted heliostats (INDC=l in Namelist HSTAT).
The location of the center of the image from each cant panel is calculated. Then
a separate Hermite series is used to represent the image from each cant panel.
This option can only be used in performance calculations with a single
aimpoint at the center of the receiver (IAUTOP=l, Namelist REC). Its
effect on an optimized system can be determined by rerunning a performance cal-
culation on the optimized system with INDC=l.
II1.F-2. When to do Fluz Calculations-Flux calculations should be done ei-
ther to design flux limited systems or to define a detailed flux map of a previously
optimized system. Therefore, flux calculations should not be done (IFLX=O) dur-
ing an initial performance calculation. It is recommended that, during system op-
timization, a grid of flux points be defined covering either the entire heat absorb-
ing surface or a known area of concern, and that up to four points from that grid
be checked during optimization to verify that flux limits are not exceeded. During
the final performance calculation, fluxes should be calculated for points over the
entire heat absorbing surface to verify that flux limits have not been exceeded at
any other points than those checked during optimization.
1II.G. Time Independent Losses
The hourly and seasonal variation of: a) atmospheric attenuation from the he-
liostat to the receiver, b) receiver radiation and convection losses, and c) piping
insulation losses are assumed negligible. In addition, mirror and receiver reflec-
tivity, the thermal to electric conversion efficiency, and parasitic loads are repre-
sented by constant time averaged values.
77