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

1II.E. Shadowing and Blocking
Shadowing occurs when one heliostat is in the shadow of one or more neigh-
bors. Blocking occurs when a part of the unshaded region of the heliostat cannot
be seen from the receiver because of its neighbors. Shadowing and blocking are
strongly time and position dependent.
Shadowing (blocking) is calculated by projecting the neighboring heliostats
along the sun (tower) direction onto the plane of the heliostat being considered.
The area that is shaded (blocked) is then calculated analytically. Twelve nearest
neighbors are considered in the calculation.
Two options are provided for overlapping of shadowing and blocking on a he-
liostat. For ISB=O (Namelist HSTAT) the shading and blocking are assumed to
never overlap. This is generally the case except at low sun angles. This approx-
imation is an upper bound on shading and blocking losses. For ISB=1 the shad-
ing and blocking are assumed to always overlap. This approximation is a lower
bound on the losses. The default choice is the conservative one (ISB=O).
III.E-1. Eflect of Slip Planes on Shadowing and Blocking-As explained in
1I.C-1, heliostats have to be removed from slip planes in radial stagger layout pat-
terns. These missing heliostats will reduce the shadowing and blocking. DELSOL
assumes that the shadowing and blocking losses are reduced by the ratio of the
number of missing heliostats to the total number of heliostats in a zone. For ex-
ample, if 5% of the heliostats are missing due to slip planes, a 10% shadowing loss
would be reduced to 9.5%.
1II.E-2. Tower Shadow-DELSOL calculates the effect of the shadow cast by
the tower and receiver. The tower and receiver shadow is modeled as that cast by
a vertical cylinder of height TOWL meters (above the plane of the heliostat piv-
ots) and diameter of TOWD meters. Both values scale with THT during system
optimization, so that the ratio of these values to the THT specified in an initial
performance run remains constant as THT is varied during the optimization. For
this reason, the values should be carefully and correctly specified during an initial
performance run (IPROB=4) and should not be input during the optimiza-
tion process. The default values are consistent with the default values of THT
and W:
TOWL = 175.0 m
TOWD = 10.0 m
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