Page 28 - Design of Solar Thermal Power Plants

1.2 BRIEF INTRODUCTION TO SOLAR THERMAL POWER GENERATION 21

FIGURE 1.10 Structural diagram of parabolic trough solar collector.

As shown in Fig. 1.10, a parabolic trough solar power collector consists
of a parabolic trough concentrator that tracks the movement of the sun and
a receiver tube mounted at the focal point of the paraboloid. The parabolic
trough concentrator uses a single-axis tracking concentrator, namely a
concentrator with a mirror element revolving in a one-dimensional manner
by surrounding a single axis to track the movement of the sun. The surface
of the parabolic mirror is the trajectory formed by a line moving along
a certain parabolic curve while parallel to the fixed line. Thus with a
parabolic trough concentrator that tracks the movement of the sun, DNI is
constantly concentrated on the surface of the receiver tube and creates a
focal line so that the heat transfer liquid inside the receiver tube can be
heated. High-temperature and high-pressure steam is then generated
directly or through an oilewater heat exchange system in order to partic-
ipate the thermal cycle power generation system and drive the steam
turbine to function and generate power or provide the requested steam
for industrial processes. The heat transfer liquid of the system transfers
thermal energy and is normally water/steam, synthetic oil, or molten salt.
The parabolic trough concentrator is a key component that receives and
reflects solar radiation and consists of the base, bracket, mirror, power
machine, transmission system, and control system. A typical parabolic
trough concentrator is made up of multiple units connected in series
along the axis and equipped with a power, transmission, and control
system. Normally for a parabolic trough concentrator with small radia-
tion areas, hydraulic or mechanical transmission can be applied; for one
with large radiation areas, only hydraulic transmission can be applied.
A bracket is connected to the mirror through fixtures to support and
ensure the stability of the parabolic mirror surface; its structure can be
categorized as torque tube, torque box, and space truss types; the mate-
rials are normally metals, such as steel or aluminum products, and the
processing pattern is mainly welding and punching.
Structures of the mirror can be categorized as single-layer or compos-
ite. The single-layer structure is an ultraclear glass hot-bending parabolic
trough surface that is coated with silver, whereas the composite structure