Page 263 - Design of Solar Thermal Power Plants

246 4. DESIGN OF THE CONCENTRATION SYSTEM

thermal tower power generation systems [34]. The mathematical models
of MIRVAL, FIAT LUX, and SolTrace can be used only for detailed he-
liostat field energy collection calculations and not for heliostat field
optimization. The mathematical models of HFLCAL and DELSOL,
however, can be used for the entire solar thermal tower power generation
system, including heliostat field optimization design; they can be directly
used for estimating the annual average optical performance of a large-
scale heliostat field; but for small-scale heliostat fields, their calculation
accuracies are comparatively low [34]. The main features of the above
performance-analysis programs are shown in Table 4.2 [34].
From 2003 to 2005, SENER Corp. of Spain successfully developed
SENSOL software [35], which was written in Fortran and used for thermal
economic analysis of solar thermal tower power generation systems. The
coordinate position of the heliostat can be determined based on the level
of economy. This software was applied in the system design of the Solar
Tres program in Spain.
The main heliostat field design codes in china include HFLD and HOC.
Several main heliostat field design codes are compared in Table 4.2.

4.3.2.2 Basic Idea of Concentrating Field Design
The basic idea is to apply a radial-staggered layout pattern, conduct
heliostat field layout optimization for a solar thermal tower power
generation system using conventional dual-axis tracking under the
premise of avoiding mechanical collision between adjacent heliostats
while collecting maximum energy or achieving optimal economy, as well
as optimizing results to obtain a Pareto curve under dual-objective
coordinate axes that consist of various optimal heliostat field layout
schemes. The optimized heliostat field features not only a low-unit energy
cost and good economy, but also uniform and reasonable energy
distributions.
1. Required space for heliostat free rotation [13]: a heliostat is by
nature a mirror (reflective mirror). Conventionally, a rectangular
heliostat rotating around a fixed vertical axis, which has been the
most widely used as shown in Fig. 4.15, continually tracks
variations in solar position in order to reflect solar radiation onto
the fixed target of the receiver. Because the diameter of the vertically
placed barrel-shaped cylinder created by its free rotation around
the azimuth axis is equal to the length of the heliostat’s diagonal,
during heliostat field design, feature parameter D m is defined as the
length of the diagonal plus a safety clearance of 0.3 m. During the
placement of heliostats, the spacing between two heliostats must
not be less than this value.