Page 31 - Design of Solar Thermal Power Plants

24 1. INTRODUCTION

vacuum state. A getter accomplishes the target of absorbing residual
gases by mainly by relying on physical and chemical absorption.
6. Selective absorption film. According to its working mechanism, it
can be categorized as optical interference, intrinsic absorption,
metal ceramic, or multilayered gradient film. As a general
requirement, for temperatures below 400 C, its absorptivity shall be

not less than 95%, and its reflectivity shall be less than 14%. The most
widely applied selective absorption film is composite material
absorption film, including multilayered gradient metal ceramic film
and double-layered absorption film. The multilayered gradient metal
ceramic film has a metal substrate, and the absorption layer is made of
metal and dielectric gradient film, whereas double-layered absorption
film creates two absorption layers and one or two dielectric
antireflection layer(s) on the high-reflectance metal substrate to
achieve low reflectance without reducing the absorption rate.
2
As shown in Fig. 1.12, in 2017, a 9000-m parabolic trough solar col-
lector was completed at the Beijing Badaling CSP experimental base. The
2
collector was arranged horizontally along the 3000-m northesouth axis
2
and 6000-m westeeast axis with a tracking length of 300 m. The bracket
was mounted by applying a torque tube structure and selecting an
independently developed sandwich-structure glass mirror, the technical
parameters of which are shown in Table 1.3.
As shown in Fig. 1.13, the collector is of torque tube-type, the support
arm is made from rectangular steel pipe by welding, and the parabolic
mirror is made by gluing together the hot-bending glass paraboloid and
the ultrathin glass mirror. A parabolic trough solar power collector con-
tains 24 pieces of vacuum receiver tubes; the metal absorber pipe inside

FIGURE 1.12 Beijing parabolic trough solar power collector. Provided by the Institute of
Electrical Engineering, Chinese Academy of Sciences, 2017.