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

111.1. Relationship Between Performance and ODtimization Calculations
In order to do a system optimization, the results of an initial performance cal-
culation must be used. It is also suggested that a final performance run be done
on any system which was optimized, in order to get a more accurate field perfor-
mance calculation and in order to get a more accurate annual energy calculation
for predicting levelized energy costs.
During optimization, DELSOL must recalculate the zone by zone annual aver-
age and design point optical performances at each new tower height and receiver
size. The code does this by “scaling” the results of a detailed performance cal-
culation. The results which are scaled are the descriptions of heliostat images on
the receiver for each zone. That is, the initial performance run calculates helio-
stat 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 com-
bined with the design point and annual average field and system efficiencies to
calculate design point power and annual energy.
The cosine, shadowing and blocking, and atmospheric attenuation losses used
in the system optimization are described in Section IV.A, and all make a distinc-
tion between design point and annual average losses. However, the annual aver-
age heliostat image is used for both design point power and annual energy cal-
culations during the optimization. This has two possible effects. First, if actual
design point spillage is significantly different from the annual average spillage,
then the optimization may over- or underpredict the design point receiver ther-
mal power. This difference would become apparent if a final performance calcu-
lation were done on that optimized system, during which the correct design point
spillage would be calculated and used. This difference is usually less than 1%.
Second, the shape of the design point hehostat image may be different from the
annual average. This would result in a different flux distribution being predicted
during system optimization than during a final performance calculation. Thus, a
design which was optimized to meet flux levels at certain locations on a receiver
may actually exceed or fall short of those flux levels when a more accurate perfor-
mance calculation is done on the system. This effect could be up to a 10% differ-
ence in predicted flux levels but is typically less than 5%.
Because the results of an initial performance run are used during system op-
timization, it is strongly recommended that the system for which the optimum
performance is calculated be as close as possible to the final configuration chosen
during system optimization. Specifically, a north facing cavity or flat plate should
have the variables IREC and INORTH set consistently, in addition to having re-
ceiver and tower dimensions chosen as wisely as possible.
Similarly, the system configuration should not be changed in a final perfor-
mance run if it is desired to determine the performance of a previously optimized
system. Further, the capital costs of equipment are only calculated during the I
optimization process and are not modified in a final performance run. Thus, if
92