Eckhard LUpfert, German Aerospace Center (DLR), Plataforma Solar de Almeria
Klaus Pottler, German Aerospace Center (DLR), Plataforma Solar de Almeria
Wolfgang Schiel, Schlaich Bergermann und Partner (SBP), Stuttgart

Solar thermal power plants are about to continue their market introduction with large solar fields for 50 MW plants and other. The successful construction of para­bolic trough collectors in large series requires an appropriate measurement and quality control program in order to achieve the designed optical and thermal per­formance. The collector quality can be increased significantly by correct alignment of the large reflector and receiver areas. A number of tools have been developed for efficient supervision of assembly jigs, and samples during fabrication. The meas­urement techniques have been applied initially for the purpose of prototype devel­opment. Their use can be extended to quality control in series fabrication, if evalua­tion is fast enough. The available tools include digital photogrammetry, reflector and receiver flux test methods, oil flow and temperature measurements. Their appli­cation in parabolic trough collector technology results in reduced cost for quality control in series manufacturing and increased collector performance.

Overview

The optical performance of solar concentrating collectors is very sensitive to inaccuracies of components and assembly. Because of a finite sun-shape and extant imprecisions of the collector system (e. g. steel structure, tracking, receiver alignment, mirror alignment, mirror shape and mirror specularity) the interception of light at the focal receiver is af­fected. To reach maximum performance through optimal component alignment a mix of measurement techniques should be used for quality control measures. This comprises incoming inspection, mounting of the module structures, assembly of the collectors and final inspection of the collector system. High precision 3D-coordinates of important mount­ing points may be derived from close range photogrammetry, slopes by water levels or electronic inclinometers, distances by vernier callipers, gauge bars or laser range finders and surveyor’s levels. Alignment errors can be derived from the evaluation of digital pho­tos. The optical collector quality can be analysed by measuring the flux density in the vicin­ity of the receiver. Thermal performance analysis is possible for any part of the collector field with a flexible installation of temperature sensors and ultrasonic flow meters without installation needs in the heat transfer loop.