Page 268 - Design of Solar Thermal Power Plants

250 4. DESIGN OF THE CONCENTRATION SYSTEM

The value of DR max may be great so that the area of the heliostat field
is great.
During program design, as a decision variable, the radius of the
first ring where the heliostat has been placed shall be optimized
before selection, whereas the radii of other rings shall be calculated
based on the radial spacing between each ring and the ring previous
to it:
R mþ1 ¼ R m þ DR min þ R min max ðDR max DR min Þ;
(4.14)
0 < R min max < 1

4. Calculation of circumferential spacing: in design, the first heliostat
on the essential ring is placed on a negative section of the y-axis.
The angle between it and the negative section of y-axis is assumed to
be q; then the positions of other heliostats can be calculated based on
the azimuthal angle between them and adjacent heliostats
(especially those located in the left front).
a. Calculation method for minimum azimuthal spacing: as the
heliostat must reflect the solar beam onto the receiving tower,
there shall be a certain azimuthal angle between adjacent front-
and-back heliostats that avoids significant shading and blocking
losses.
For a staggered ring:

qðm; nÞ min ¼ Angleðm; nÞ min Angleðm 1; nÞ

(4.15)
¼ arcsin½D m =ð2R m 1 ފ
For the second and other heliostats on the first ring:

qðm; nÞ ¼ Angleðm; nÞ Angleðm þ 1; n 1Þ

min min
(4.16)
¼ arcsin½D m =ð2R m ފ
For the second and other heliostats on the essential ring:

qðm; nÞ ¼ Angleðm; nÞ Angleðm 1; n 1Þ
min min

¼ arcsin½D m =ð2R m 1 ފ (4.17)
As shown in Fig. 4.18, the solid black circle refers to well-placed
heliostats, the hollow solid line circle refers to the position of
heliostats on adjacent rings with the minimum azimuthal angle, and
the dotted-line circle refers to the position of heliostats with the
maximum azimuthal angle.
b. Calculation of maximum azimuthal spacing: the designed
maximum azimuthal spacing in this book ensures no blocking in