Page 48 - Design of Solar Thermal Power Plants

1.2 BRIEF INTRODUCTION TO SOLAR THERMAL POWER GENERATION 41

FIGURE 1.27 Concentrator mirror surface errors. (A) Canting position error. (B) Mirror
slope error.

error and slope error, in which the incidence point position of solar
radiation is inconsistent with the expected position and is subject to
position error; this position error is mainly caused by installation,
namely support structure location error. Fig. 1.27A indicates an
incident solar direct radiation position error caused by altitude
angle error due to inappropriate installation of the support
structure of the reflective surface.
A surface slope at the incidence point inconsistent with the
theoretical value is subject to slope error, namely the normal error on
the reflective surface, which is related to the mirror manufacturing
process, field assembly, temperature, gravity deformation, wind
force, and other error factors (refer to Fig. 1.27B).
20. Efficiency of concentration field. This is the ratio of solar radiation
energy (kWh) reflected or transmitted by the concentration field
into the aperture of the receiver to the total direct normal solar
radiation energy (kWh) on the mirror surface of the concentration
field within unit time. According to Eqs. (1.1) and (1.2), due to the
position variation of the sun for the parabolic trough concentrator
and heliostat, the efficiency of the concentration field changes
according to different solar angles, whereas the efficiency of the
dish concentrator does not change with the solar angle.
21. Annual efficiency of the concentration field. This is the ratio of the
solar radiation energy (kWh) reflected or transmitted by the
concentration field into the aperture of the receiver within a year to
the total incident solar direct normal radiation energy (kWh) on the
mirror surface of the concentration field.