Photogrammetry: A Powerful Tool for Geometric Analysis of Solar Concentrators and Their Components

Abstract

Digital close range photogrammetry has proven to be a precise and efficient measurement technique for the assessment of shape accuracies of solar concentrators and their components. The combination of high quality mega-pixel digital still cameras, appropriate software and calibrated reference scales in general is sufficient to provide coordinate measurements with precisions of 1:50,000 or better. The extreme flexibility of photogrammetry to provide high accuracy 3-D coordinate measurements over almost any scale makes it particularly appropriate for the measurement of solar concentrator systems. It can also provide information for the analysis of curved shapes and surfaces, which can be very difficult to achieve with conventional measurement instruments. The paper gives an overview of quality indicators for photogrammetric networks, which have to be considered during the data evaluation to augment the measurement precision. A selection of measurements done on whole solar concentrators and their components are presented. The potential of photogrammetry is demonstrated by presenting measured effects arising from thermal expansion and gravitational forces on selected components. The measured surface data can be used to calculate slope errors and undertake raytrace studies to compute intercept factors and assess concentrator qualities.Keywords: Photogrammetry, Quality Control, Concentrator Analysis, Parabolic Trough Collector, Ray-Tracing INTRODUCTIONThe 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. tracking, receiver alignment, mirror alignment, mirror shape and mirror specularity) the interception of light at the focal receiver is reduced. High precision photogrammetry is an appropriate tool to measure 3D-coordinates of concentrator support points and mirror surfaces, especially for the analysis of large concentrators [1,2,3]. In contrast to measurement tools for monitoring solar flux in the focal region [4,5], the photogrammetric method directly delivers coordinates of selected test points and thus allows performance assessments of the concentrator to be made. Whereas other surface evaluation methods are limited to special shapes, e. g. to point focusing devices [6] (such as the (V)SHOT-method [7,8] or the SCCANmethod [9]), or to linear parabolic concentrators (indoor [10,11] or outdoor laser ray trace [12]), photogrammetry is a universal method for testing almost any type of concentrator or structure.

A new approach towards image based virtual 3D city modeling by using close range photogrammetry

“…Shortis and Beyer (2001) explained about sensor technology for close range photogrammetry and machine vision. Pottler et al, (2005) studied about photogrammetry as a powerful tool for geometric analysis of solar concentrators and their components. Hosseininaveh et al, (2013) discussed about the comparison of dense matching algorithms for scaled surface reconstruction using stereo camera rigs.…”

Shape Measurement of Solar Collectiors by Null Screens

“…Both methods for testing optical system are useful mainly for surfaces of revolution. Previous works (Shortis & Johnston, 1996;Pottler & Lüpfert, 2005) have described the application of photogrammetry to the characterization of solar collectors. Briefly, close-range photogrammetry involves the use of a network of multiple photographs of a target objet (a solar collector component in this case) taken from a range of viewing positions, to obtain high-accuracy, 3D coordinate data of the object being measured.…”

Automated high resolution measurement of heliostat slope errors

“…For the measure of local shape deviation of solar concentrators photogrammetry can be used [4]. However, as the measured surface has to be equipped with a large number of target points which are used as individual surface measurement points, the measurement is a time consuming task which is not appropriate for the measurement of large numbers of mirrors.…”