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

system costs would be at 160 meters, this information would be available in the
output optimization summary. However, the energy costs associated with these
systems in the optimization summary should not be viewed as real energy costs,
due to the assumptions involved in calculating them, but may be viewed as rela-
tive comparative costs. A final performance calculation would still be needed to
give DELSOL’s most accurate prediction of energy costs.
1V.F. Sensitivity of Energy Costs to Variation of Design Parameters
Generally, the cost of energy is not very sensitive to modest variations of the
design parameters away from the optimal values determined by DELSOL. It is
important for the user to remember that the minima are shallow. First, the broad
optimum means that a very fine (and time consuming) grid of variables is not
needed. Second, the designer has the freedom to vary the system to maximize
other considerations besides cost of energy. For example, DELSOL may select a
large height to width ratio for a flux limited external receiver. However, a more
modest aspect ratio may be desired for engineering or other reasons. The opti-
mization can be repeated with smaller H/W ratios in order to see what the cost
of energy penalty is. The energy cost differential may be so small that the other
design considerations dominate and a smaller H/W ratio than the DELSOL mini-
mum will be selected.
Small changes in the input generally produce small changes in the energy cost
but can produce large changes in the optimum value of the design parameters.
This is also a consequence of the shallow minima in the energy cost vs. design
variables. This effect is often not understood by users. It seems counterintuitive
that one can set out to design systems for the same application and yet produce
significantly different designs just because of small difference in the input vari-
ables. If one were to compare energy costs, however, the different designs would
probably be nearly identical on a cost basis.
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