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

thrown away due to storage being full at any time of the year, therefore avoid-
ing the necessity of doing detailed energy flow accounting while optimizing other
system design parameters. However, it is possible that for north biased heliostat
fields some excess energy will be thrown away due to full storage at days other
than the longest operating day, due to a combination of system efficiencies and
insolation levels. Further, it is possible that choosing a smaller storage tank and
discarding (not collecting) some energy may be more cost effective than never dis-
carding energy. For an otherwise completely optimized system, DELSOL allows
the user the option to determine the most cost effective storage size.
Storage optimization is requested during the optimization process in DEL-
SOL (Namelist OPT) by specifying the variables ISTR and NSTR. ISTR, when
nonzero, is the ratio of the maximum storage size to be examined to the storage
size calculated by DELSOL at the longest day for the otherwise optimized sys-
tem. NSTR is the number of equally spaced storage sized from zero to ISTR to
be evaluated.
Although storage optimization is requested during system optimization, the
storage optimization is actually performed during a final performance calcula-
tion on an otherwise optimized system (IPROB=l). Thus, the storage size and
cost printed during system optimization will be the nonoptimized stor-
age. During the final performance run, when energy accounting vs. time is oc-
curring, the storage size will be varied, storage costs will be recalculated, and the
actual amount of energy discarded for each different storage tank size will be cal-
culated. The optimum storage size, along with annual energy data and adjusted
capital and energy costs, will be printed out ahead of the annual power produc-
tion detailed output.
The default values (ISTR=O, NSTR=l) allow no storage optimization. Re-
running a specified optimum design for detailed performance for this case would
give system performance for the maximum size storage capacity determined ini-
tially.
At this point a distinction should be made between physical storage size
and the two values SMULT and capacity factor. SMULT, which is a user input
(Namelists OPT and NLEFF), is the factor multiplying the minimum require-
ment for thermal power at the base of the tower to meet the specified power de-
livered to the process at the design point. Thus, SMULT, or the solar multiple,
does not specify a storage size (cost) because it does not make a distinction be-
tween storing energy and discarding energy. The solar multiple is only used to
size the field and receiver with respect to the defined plant rating. On the other
hand, capacity factor (printed during system optimization) is a calculated value
of the ratio of time operating during a year to total time in a year. Capacity fac-
tor is calculated in DELSOL by calculating the total amount of energy produced
by the heliostat field during the year, reducing that value by annual average sys-
tem efficiencies, and dividing that value by the total time in a year. Again, the
assumption is made that no energy is discarded (rather than being stored), and
110