A flux mapping system able to measure the flux distribution of dish/Stirling systems in planes perpendicular to the optical axis was built and operated at the Plataforma Solar de Almeri´a (PSA). It uses the indirect measuring method with a water-cooled Lambertian target placed in the beam path and a CCD-camera mounted on the concentrator taking images of the brightness distribution of the focal spot. The calibration is made by calculating the total power coming from the dish and relating it to the integrated gray value over the whole measurement area. The system was successfully operated in a DISTAL II stretched membrane dish and in the new EURODISH in order to characterize their beams and improve the flux distribution on their receivers.

The knowledge of the absorber surface temperature distribution is essential for efficient operation and further development of solar thermal high temperature receivers. However, the concentrated solar radiation makes it difficult to determine the temperature on irradiated surfaces. Contact thermometry is not appropriate and pyrometric measurements are distorted by the reflected solar radiation. The measurement in solar-blind spectral ranges offers a possible solution by eliminating the reflected solar radiation from the measurement signal. The paper shows that besides the incoming solar radiation and the absorber emittance, the bi-directional reflection properties and the temperature of the object are determining for the required selectivity of the spectral filter. Atmospheric absorption affects the solar blind pyrometric measurements in absorption bands of CO2 and water vapor. The deviation of temperature measurement due to atmospheric absorption is quantified and the possibilities and limitations of accounting for the atmospheric absorption with models based on radiation transfer calculations are discussed.

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.

With 620 MWel in operation [1] and more than 2.000 MWel under construction, concentrated solar power (CSP) experiences a renaissance mainly in Spain and the USA, but also in many other countries in the earth’s sunbelt. Due to their large capacity (50 MWel and more) and thus large investment, CSP projects are characterised by an extensive project development process. In several stages of this process, mathematical models of the system predicting its energy yield are required, among others to: • assess single CSP projects (e.g., feasibility or due diligence studies), • compare different CSP concepts (e.g., technology, site), • optimise a project (e.g., solar field size, storage capacity), • investigate the influence of component characteristics (e.g., receiver characteristics), • optimise the operation strategy (e.g., on-line surveillance) or to • assess system performance during commissioning. The models used for these different tasks differ in complexity and accuracy, e.g. the accuracy of a model used for project assessment during commissioning has to be higher than a model used for a pre-feasibility study. At the moment, numerous modelling approaches exist and every project developer uses his own system model and assessment methodology. This confusing situation hinders the acceptance of CSP technology by potential investors. This paper presents a methodology for structuring systems into sub-systems. This is the first step towards a standardized modelling approach for CSP systems. It is not the intention of the authors to present a final model and assessment methodology but to start a broader discussion on this important topic. In fact, it aims at initiating an international working group, devoted to the definition of guidelines for modelling, simulation and assessment of CSP systems, covering all CSP technologies such as solar towers, parabolic troughs, linear Fresnel collectors and solar dishes.

Analysis of geometry and optical properties of solar parabolic trough collectors uses a number of specific techniques that have demonstrated to be useful tools in prototype evaluation. These are based on photogrammetry, flux mapping, ray-tracing, and advanced thermal testing. They can be used to assure the collector quality during construction and for acceptance tests of the solar field. The methods have been applied on EuroTrough collectors, cross-checked and compared. This paper summarizes results in collector shape measurement, flux-measurement, ray-tracing, and thermal performance analysis for parabolic troughs. It is shown that the measurement methods and the parameter analysis give consistent results. The interpretation of the results and their annual evaluation give hints on identified relevant improvement potentials for the following generation of solar power plant collectors.