Page 261 - Design of Solar Thermal Power Plants

244 4. DESIGN OF THE CONCENTRATION SYSTEM

4.3.1 Basic Operation Modes of the Heliostat Field and Basic
Design Parameters

4.3.1.1 Operating Modes of the Heliostat Field
The function of a heliostat field is to provide a receiver with as much
energy as possible while ensuring system safety and service life. Local
overtemperature conditions and frequent thermal shocks to a receiver’s
heat absorber have adverse effects on heat absorber servicing and safety.
By following the above principles, the control modes of the heliostat
field can be divided into manual and automatic modes (refer to Table 4.1
for details). The manual mode includes a standby mode and an operation
control mode, and the automatic mode includes a strong wind mode and
a breeze mode. The breeze mode includes a normal operating mode and a
beam characterization system (BCS) calibration mode. The normal oper-
ating mode can be divided into daytime and night modes based on time of
day. The daytime mode can be further divided into a “ready point” mode
and a normal tracking mode. The special modes include a cleaning mode
and an overhaul mode.

4.3.1.2 Design Parameters
The heliostat field control system controls the heliostat field by setting
the working modes of each heliostat, either one by one or in sections and
groups.
1. Working conditions of heliostat field design: in general, the normal
working ambient air temperature range is 10 to 45 C. For wind

speeds not more than 13 m/s, normal heliostat functioning can be
ensured; for wind speeds not more than 20 m/s, the heliostat should
not be damaged under any working status; in the protection state,
the heliostat should not be damaged for cases in which the wind
speed is not more than 36 m/s.
2. Viability under special extreme conditions
a. Extreme temperature tolerance results in no damage to heliostat
components from 40 to 60 C.

b. Seismic tolerance intensity is 8 , especially for heliostat

foundation stability.
c. Weather resistance: various components of the heliostat can
withstand rain, snow, sandstorm invasion, and outdoor
temperature variation without damage during service life;
various metal components shall be free of any corrosion.
d. Hail resistance: the reflective surface of the heliostat shall
withstand hail impact with hail diameter of 20 mm along the
direction parallel to the normal of the mirror surface without any
damage.