Page 139 - Design of Solar Thermal Power Plants

124 3. GENERAL DESIGN OF A SOLAR THERMAL POWER PLANT

shadow of the current heliostat contour on the horizontal ground plane
overlaps with the shadows from the two neighboring heliostats and the
shadow of the solar tower. The current heliostat and its neighboring
heliostats are marked by green dots and lines, and the tower is marked by
red dots and lines. Fig. 3.2E marks the shaded mirror region of the current
heliostat by neighboring heliostats and the solar tower.
Fig. 3.2F shows the geometric topological invariance of a mirror point
of the current heliostat inside the shade cast by a neighboring heliostat
under shading projection from the mirror surface plane to the flat ground
plane. If the shading projection of a sampled mirror point of the current
heliostat is shaded by a neighboring heliostat or the tower, the mirror
point should be shaded from the incident sun beam, i.e., if a mirror point
of the current heliostat is shaded by a neighboring heliostat, the shading
projection of the mirror point is in the intersection of the shade regions of
the current heliostat and the neighboring heliostat in the flat ground
plane, as Fig. 3.2F shows.

3.2.3 Two Specific Versions of Heliostat Optical Code
HOC based on the BRT and new shading-and-blocking methods for a
solar tower power plant was developed using MATLAB, as Fig. 3.3
shows. The following two versions of HOC are for the cavity receiver and
cylinder receiver, respectively.
Fig. 3.3AeD show the specific version of HOC for the DAHAN solar
tower power plant in Beijing. There are 100 azimuth-elevation tracking
heliostats in the solar field, and the total tower is 118 m high. The mirror
surface of the heliostats is 10 m wide and 10 m long; it is composed of 8
rows 8 columns of square mirror facets, and each mirror facet is
1.25 m 1.25 m. The target center is 74.5 m higher than the ground plane.
Fig. 3.3EeG show the cylinder central receiver solar field layout
(CCRSFL) version of HOC. A CCRSFL adopts the traditional radial-
staggered pattern layout for a heliostat field. In CCRSFL, given the pa-
rameters of tower height, heliostat size, and receiver size, the heliostats
are initially arranged as a compact circular field with sufficient total
mirror area; then the heliostat field grows gradually by increasing the
radial spaces between adjacent heliostat rings during the optical optimi-
zation process. The optimizing objective function collects the maximum
annual solar energy from the receiver aperture. After first-stage optimi-
zation of solar field layout, the solar field is trimmed by selecting the
needed number of heliostats that have higher annual optical efficiencies.
The trimmed heliostat field is optimized further through a second stage
similar to the first. CCRSFL can efficiently simulate the concentrated solar
flux map of heliostats on the receiving surface using only a pair of cross-