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

determined by DHOPT (Namelist BASIC). The larger DHOPT is, the farther the
heliostat separations are allowed to vary from the initial values in searching for
an optimum. However, the larger DHOPT becomes, the larger are the potential
errors in interpolation and differentiation.
To prepare for field buildup, the code does four preliminary calculations for
every zone. First, it finds the “best” aspect ratio at each density. If the land
and wiring costs are negligible, the best aspect ratio at a given density would
be the aspect ratio that gives the minimum shading and blocking. Second, the
code finds the density that gives the maximum average performance/cost ratio
(PCR) for that zone. When the zone is first added to the field, it will be at this
density. Third, DELSOL finds the marginal value of increasing the density be-
yond the density that optimizes the average PCR. The marginal value is defined
as the change in the busbar energy cost for adding or subtracting one heliostat
from that zone. The marginal values decrease with density beyond the density
that optimizes the average PCR. These marginal values determine how the den-
sity in the zone is increased during field buildup after the zone has been added to
the field. Finally, when the first three calculations are completed for every zone,
DELSOL ranks the zones accordingly from maximum to minimum average PCR.
This ranking determines the order in which zones will be added to the field.
Field buildup proceeds as follows:
1) The zone with the best average PCR is used as the initial field zone; then,
1
2) The unused zone with the best average PCR is added to the field and
the density of all zones already in the field is increased. The number of
heliostats to be added to each zone already in the field is determined by
requiring that the marginal value of adding one more heliostat to any
zone is the same. (If the marginal values were unequal an optimum field
would not exist since the energy cost could be lowered by moving a heliostat
from a lower to a higher marginal value zone.);
3) Step (2) is repeated until: (a) all design powers are achieved; (b) a flux
limit constraint is exceeded; or (c) all the zones have been added to the
field.
I V. B-9. Effectiveness of Heliostat Density Opt irnizat ion-DELSOL optimizes
heliostat densities to produce a given amount of annual energy, E, at a minimum
energy cost. However, in many cases the optimization results in a field layout
having a lower annual efficiency/design efficiency ratio, thus producing less an-
nual energy at a constant design point power. That is, although the annual ef-
ficiency after optimization will be higher (requiring fewer heliostats for a given
amount of annual energy), the design point efficiency might be increasing even
more rapidly. Since the heliostats are only added until the design point power
is reached, fewer heliostats would be in the field than if the annual energy were
kept constant, so the annual energy might not be as large as before. Thus, capital
cost of heliostats and annual energy both might decrease. Then, if field cost is a
102