Page 167 - Design of Solar Thermal Power Plants

152 3. GENERAL DESIGN OF A SOLAR THERMAL POWER PLANT

Collector tube center
2.01m
0.04m
1.00m
Glass 1 1.33m
Copper
tube Copper 2 Glass cover Copper 3 Glass 2
Copper 1 absorber tube Vacuum annulus

Cartridge heater

Exterior
disc-type
heater absorber absorber absorber absorber tube 4
Interior
tube 1 tube 2 tube 3 1.00m
disc-type
heater 1 1.67m
2.00m
FIGURE 3.21 Positions of temperature measuring points on the test platform of heat loss
coefficient of NREL evacuated tube [22].

temperature measuring point and sampling frequency, as well as the
temperature and color of the interior wall.
Fig. 3.21 has indicated positions of temperature measuring points on
the evacuated tube test platform of the National Renewable Energy
Laboratory (NREL), which is part of the Department of Energy (DOE)[22];
the heater material is copper.
Standards currently suitable for testing the thermal performance of
parabolic trough solar collectors include the American standard ANSI/
ASHRAE 93 “Methods of Testing to Determine the Thermal Performance
of Solar Collectors” [23] and European standard EN 12975-2 “Thermal
Solar Systems and ComponentsdSolar Collectors: Part 2: Test Methods”
[24]. Although these two standards have already been compared by certain
literature, they have focused on low-temperature thermal utilization of
solar energy of flat-plate-type and vacuum-tube-type solar collectors.
Working temperatures of these two types of solar collectors are normally
less than 80 C; nevertheless, working temperature of the parabolic trough

solar collector falls in a range of 100e400 C.

3.3.2 Current Status of Measurement Methods for Parabolic
Trough Collector Thermal Performance
3.3.2.1 Current Overseas Research Status of Thermal
Performance of Parabolic Trough Collectors
Ever since 1970s, commercial products of concentrating solar collectors
began to be developed, which made the DOE in the United States and