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

IV. System Optimization Calculations
The purpose for which DELSOL was written was to allow quick and simple
comparisons of different systems to determine which system produced the lowest
energy cost. Specifically, systems with different receiver/tower dimensions, dif-
ferent power levels, heliostat spacings, and storage capacities can be compared
without performing multiple executions of the code with different sets of input.
Further, the different systems are compared during a single run by scaling system
performances from an initial performance calculation, so that a time consuming
performance calculation is not needed or used during system optimization, thus
resulting in the other advantage of using DELSOL to compare different systems.
Although both performance and energy values are used during optimization to
compare different systems, it must be remembered that the optimization pro-
cedure is an approximation calculation. Thus, it is important that the user use
DELSOL to do a final, more accurate, performance calculation on any system
which is chosen to be best during system optimization based on levelized energy
cost.
Because the optimization is based on the cost of energy, calculations are done
during system optimization to dqtermine the cost of individual system compo-
nents and to determine the cost of certain economic assumptions. The methods in
Chapter 5 for determining costs are used during system optimization.
During system optimization, DELSOL not only compares different systems,
but also defines the heliostat field to meet the required power level. This is the
only time when DELSOL changes the field dimensions and number of heliostats.
In fact, that is an essential part of the optimization. The optimization compares
systems of similar design point powers, but since field efficiencies can vary be-
tween systems, the number of heliostats must be varied during optimization to
reflect that difference in efficiencies for the same power level.
1V.A. Optimization Methods for Calculating Performance and Energy
DELSOL must recalculate the zone by zone annual average and design point
optical performances at each new tower height and receiver size, as shown in Fig-
ure IV-1, in order to design a system which produces the requested design point
power and in order to do a comparison of energy cost. The code does this by
“scaling” the results of a detailed initial performance calculation. The results
which are scaled are the descriptions of heliostat images on the receiver for each
zone. That is, the initial performance run calculates heliostat images for each
zone for each time step, and from that information calculates an annual average
heliostat image for each zone. This annual average heliostat image is then scaled
with tower height during system optimization, and is combined with the design
point and annual average field and system efficiencies to calculate design point
95