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

Only one design point and one annual average loss calculation is done during
system optimization, and the results are used for all systems examined.
I V. A - 9. Atmospheric Att e nuation-The atmospheric attenuation is exactly re-
calculated for every tower height and receiver examined during system optimiza-
tion.
1V.A-4. Tower Shadow Scaling-DELSOL accounts for the tower shadow as
described in Section 1II.E-2. The tower shadow as calculated or specified in an
initial performance run is scaled with tbwer height during optimization. That is,
the last specified tower shadow (TOWL, TOWD in Namelist REC) is scaled by
the ratio of the current tower height to the tower height specified in the initial
performance run. Thus, it is suggested that TOWL and TOWD be specified in
the initial performance run to match the tower dimensions, and then that these
variables not be changed during optimization input.
I V.A-5. Receiver Losses-Receiver design point losses are calculated using the
algorithms described in Section 1II.G-3, depending on the receiver dimensions of
each system examined during system optimization. It is assumed, as for a final
performance calculation, that receiver losses represented as an efficiency do not
vary with time of day or year, so annual receiver efficiencies are the same as de-
sign point efficiencies.
1V.A-6. Other Component Losses-Components downstream from the receiver
have simple loss calculations, as described in Section III.G, and so these losses are
calculated as described in that Section. These losses are assumed to be time inde-
pendent, so annual efficiencies are the same as design point efficiencies. However,
the turbine annual efficiency is assumed to equal its off-design point ef-
ficiency, as represented by the value ETAREF x FEFF (Namelist NLEFF). This
worst case assumption is made because the code does not know during optimiza-
tion the amount of time the turbine will actually have enough power to run at its
rated capacity. The actual annual efficiency, and therefore the amount of annual
energy, will always be higher than this assumption would indicate. This assump-
tion could and usually does cause the largest difference in predicted annual energy
(levelized energy cost) between an optimization calculation and the comparable
final performance calculation on the same system. Since the final performance
calculation is more exact, its annual energy prediction and levelized energy cost
values should be used if a discrepancy exists with system optimization predic-
t ions.
The turbine annual efficiency assumption is not a very good assumption for
systems which have reasonable quantities of storage to supplement power from
the field, since for those cases storage will be used to operate the turbine at full
power. The assumption was originally made based on water-steam systems. Al-
though the assumption affects the actual energy and cost values calculated during
optimization, the comparison determining which system is better should only be
slightly affected, and so the assumption is acceptable for this purpose.
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