Page 171 - Design of Solar Thermal Power Plants

156 3. GENERAL DESIGN OF A SOLAR THERMAL POWER PLANT

collector all day long. In case that the single axis platform is used for
testing, or a linear concentrating collector uses its original tracking/
driving device, the range of near-vertical incidence must be determined.
The testing standard has also provided the method to obtain this angular
range, within which the decrease of thermal performance does not exceed
2%. The testing standard has strict requirements on the variation of
measurement parameters. These parameters include heat-transfer fluid
inlet temperature of collector, temperature increase of heat-transfer fluid
after passing through the collector, product of heat-transfer fluid flow rate
and specific heat capacity, ambient air temperature and solar DNI.
During the period from 1974 to 1980, a few of tracking solar collector
testing research institutions were established in America. Although they
were designed and completed before ASTM testing standard being
published, basic principle of ASHRAE 93-77 reserved in ASTM standards
served as the design foundation for these test platforms; in addition,
many test platform designers also participated in the solar energy sub-
committee of ASTM. It was important these research institutions
focused on the design of linear concentrating tracking parabolic trough
collectors. It had reflected that when these works were performed, linear
concentrating parabolic trough solar collectors had already been close to
commercialization and manufactured by some American companies. It
was also noticeable that each of these research institutions had biaxial
rotation test platforms; by controlling the tracking direction, they could
achieve the vertical incidence of solar radiation on aperture of receiver of
collector. Thus thermal performance testing for collectors could be per-
formed in most times of the day.
In 2010, with the support from the NREL published the performance
testing instruction for large-scale parabolic trough solar systems, and
offered basic principles of two test methods, namely short-term steady
state test and multiday continuous test method. The instruction aimed at
creating the official PTC52 concentrating solar power generation perfor-
mance testing standard of the American Society of Mechanical Engineers;
according to the plan, the standard included other parabolic trough
concentrating solar power generation technologies. However, it normally
costs years of time to complete the preparation and approval works
related to an official performance testing standard.
As a matter of fact, before carrying out this research, the laboratory had
already carried out loop test on SEGS parabolic trough collectors (refer to
Fig. 3.23). Furthermore, for technologies related to the performance of
parabolic trough collectors, the laboratory had carried out a series of
research works, and published the respective research reports (e.g., out-
door measurement of optical performance of the vacuum-tube-type
parabolic trough evacuated tube, pipeline modeling of parabolic trough
thermal collection system, rapid analysis on parabolic trough collector