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

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IV.A-7. Calculation of Annual Energy During System Optimization-In order
to determine which system has the best levelized energy cost, an approximate cal-
culation of annual energy is done during system optimization. This calculation
makes several assumptions. First, the calculation uses the annual performance
as described above. This annual performance is represented as a field efficiency
multiplied by a balance of plant efficiency. Remember that the assumed annual
turbine efficiency approximation causes the largest error in this calculation. The
field area as described below is combined with the average annual insolation, as
calculated in an initial performance run, and the plant efficiencies to calculate
a gross annual energy. It is assumed during optimization that storage is large
enough so that no energy is ever discarded (no heliostats ever deactivated due
to excess power). Annual energy is calculated by subtracting operating and non-
operating parasitic losses, based on hours of operation from the field and from
storage only as calculated during the initial performance run. Finally, net annual
energy is calculated by incorporating the maintenance outage factor into the pre-
dicted energy value. Note that, contrary to what is done in the performance cal-
culations, time is not considered directly in calculating annual energy. Time is
only considered indirectly as, during an initial performance calculation, it affected
the calculated yearly insolation and hours of operation which are then used dur-
ing optimization.
1V.B. Heliostat Field BuilduD
During optimization, DELSOL works with the field defined by the minimum
and maximum field dimensions and the heliostat densities in each zone, for which
performances were calculated during an initial performance calculation. Each
zone is rated by a performance/cost ratio, and zones are filled in with heliostats,
starting with that zone having the best performance/cost ratio, until a requested
power is reached. This field buildup is done for each system examined during op-
timization. Field costs associated with each field buildup are calculated and used
to determine the optimum system. Once an optimum system is chosen, the he-
liostat field associated with that system remains constant during any future final
performance calculations.
DELSOL allows the user to not only build up a heliostat field zone by zone
during optimization, using default heliostat density relationships within each
zone, but also to optimize the densities of heliostats within each zone. In this
case, densities are varied around the default values, and a system is optimized to
give best cost for a constant annual energy. This optimization is done in conjunc-
tion with the field buildup procedures, and thus the total system is still designed
to a constant design point power, rather than energy. The ramifications of this
will be described in Section 1V.B-3.
IV.B-I. No Heliostat Density Optimization (IHOPT = 0)-In this case DEL-
SOL does not try to vary the default or user defined heliostat field densities, as
defined by the choice of IDENS (Namelist FIELD). A performance/cost ratio,
PCR, is determined for each zone: