Page 43 - Design of Solar Thermal Power Plants

36 1. INTRODUCTION

FIGURE 1.22 Influence of receiver tower shadow on concentration field. Provided by the
Institute of Electrical Engineering, Chinese Academy of Sciences, 2013.
mean distance between heliostats in the concentration field and
tower increases as well. Thus the heliostat’s optical efficiency
decreases, as does the annual efficiency of the entire
concentration field. Thus blocking-free design does not equate
to optimized design.
Considering the causes of shading and blocking losses, heliostats
should not be mounted too closely to each other. Based on this
point, it is possible to properly reduce mutual blocking by
restraining the distance between neighboring heliostats.
To realize comprehensive utilization of land, plants can be grown
at the bottom of the heliostat. In this case, it is necessary to analyze
the influence of the heliostat on the solar irradiation receiving of
the ground surface. As shown in Fig. 1.23, this is the mean
shading rate of the ground surface in the heliostat concentration
field of the Beijing Badaling solar tower power plant from 8:
00e16:00 on March 21. The shadow at the outer margin of the
figure indicates no shading.
d. Atmospheric attenuation loss. When solar radiation is reflected
from the heliostat to the receiver, the energy loss of solar
irradiation caused by attenuation during atmospheric
propagation is referred to as attenuation loss. The degree of
attenuation is normally relevant to the height of the sun (which