Page 277 - Design of Solar Thermal Power Plants

4.4 CONTROL DESIGN OF THE HELIOSTAT FIELD 259

FIGURE 4.21 Constitution of the heliostat tracking deviation correction system.

The current tracking angle of the heliostat consists of the initial angle,
rotation angle, and tracking deviation angle of the heliostat.
By inspecting heliostat tracking errors multiple times daily for several
days during the year, heliostat tracking deviation at a typical time can be
obtained through analysis and processing of one year or multiple years
of heliostat tracking deviation angle data and curve fitting, each day’s
corresponding tracking deviation curve can be obtained. In this way, the
corresponding daily tracking deviation curve for each heliostat can be
obtained. By utilizing this tracking deviation curve, the current tracking
angle of each heliostat shall be adjusted so that the solar spot of each
heliostat can be more precisely projected to the target position.
Based on the feature of insignificant variation of the heliostat tracking
deviation angle during a short period (such as half an hour) and
the feature of insignificant variation of the tracking deviation angle at the
same time point for consecutive days (such as 15 days), a day can be
divided into several time intervals of equal duration. During each time
interval, a tracking-deviation angle is obtained through deviation
correction inspection.
In order to facilitate reader understanding, the heliostat deviation
correction method applied at the Badaling Dahan solar tower power plant
is used for demonstration in the example that follows.
After the heliostat and deviation correction equipment in the Dahan
solar tower power plant are initiated, the measured azimuth deviation
angle and elevation deviation angle are input into the database while
recording the completion date and time of deviation correction for
interpolation calculations (refer to Fig. 4.22).
1. Manual tracking deviation correction. The operator shall input the
serial number of the heliostat that requires deviation correction