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

large enough fraction of total capital cost so that total capital cost decreases by
a greater amount than annual decreases due to optimization, the levelized energy
cost will decrease. However, for designs in which field costs are not as significant,
the annual energy might decrease more than total capital cost (as a percentage),
and thus LEC could increase due to heliostat density optimization at a constant
design point power. In either case, if the user plots energy cost vs. annual energy,
then improvement with heliostat spacing optimization can be seen.
In practice the difference in the energy costs between optimizing for a given
annual energy vs. optimizing for a given design point are small (< 1%). The dif-
ference disappears (i.e., optimizing for annual energy acts like optimizing for de-
sign point) if the non-field costs are relatively small or if the energy cost is not
changing with annual energy. Why doesn’t DELSOL offer the option of finding
the system optimized to produce a given design point power? Because it is much
more complicated and the small improvements are generally not significant.
The user should at least consider having the code do heliostat optimization.
However, if after optimization levelized energy costs are higher than before, then
density optimization will not help the user and should not be used for that prob-
lem.
1V.C. Variables With Wlich DElLSOL Optimizes
DELSOL can vary certain design variables during optimization to perform a
search for the combination of variables that minimizes the levelized energy cost
(LEC). The design variables or parameters which can be varied during a single
DELSOL run are listed in Qble IV-1. The design parameters that are held con-
stant during a single optimization search are listed in Table IV-2. This second
set of variables can be “optimized” by performing several DELSOL optimization
runs, each run having different values for these variables.
DELSOL can perform optimizations for systems with certain restraints.
These restraints are a limitation on peak incident flux allowed on the receiver,
and a restriction on the land available for the heliostat field. In this case, an op-
timum system design must have a combination of system design variables which
produces the lowest LEC and which also meets the flux and/or land constraints.
Note that the computer time required for optimization will depend on the
size of the matrix over which optimization is being performed. For instance, if
the user allows a choice of 5 values each for tower height and receiver dimensions,
then up to 5 x 5 x 5 (125) calculations will be done during optimization; but if a
choice of 10 values each is allowed, then up to 10 x 10 x 10 (1000) calculations
will be done. Thus the user is cautioned to choose the range of optimizations
carefully so as to minimize computation time.
If the values of NUMTHT, NUMREC, or NUMHTW are set to 1 (allowing no
variation in tower height or receiver dimensions), then the values which are used
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