Abstract. Ray-Tracing software tools have been widely used in the optical design of solar concentrating collectors. In spite of the ability of these tools to assess the geometrical and material aspects impacting the optical performance of concentrators, their use in combination with experimental measurements in the framework of collector testing procedures as not been implemented, to the date, in none of the current solar collector testing standards. In the latest revision of ISO9806 an effort was made to include linear focusing concentrating collectors but some practical and theoretical difficulties emerged. A Ray-Tracing analysis could provide important contributions to overcome these issues, complementing the experimental results obtained through thermal testing and allowing the achievement of more thorough testing outputs with lower experimental requirements. In order to evaluate different available software tools a comparison study was conducted. Taking as representative technologies for line-focus concentrators the Parabolic Trough Collector and the Linear Fresnel Reflector Collector, two exemplary cases with predefined conditions -geometry, sun model and material properties -were simulated with different software tools. This work was carried out within IEA/SHC Task 49 "Solar Heat Integration in Industrial Processes".

The most important standard for collector testing in Europe is the EN 12975:2006 which is applied in all the major laboratories and is the reference for the Solar Keymark certification. Besides the steady-state method, the EN 12975 allows the application of the quasidynamic method performed outdoors in natural conditions with variable radiation and ambient temperature. The available number of days for each test was investigated by analyzing meteorological data series acquired in the Solar Energy Laboratory (LES) in Lisbon since 2008 showing the advantage of the quasi-dynamic test. Both the steady-state and the quasi-dynamic methods were applied to five collectors of different types (two flat plate collectors, one evacuated tube collector with a back reflector and direct flow circulation, one evacuated tube collector with heat pipes, and a CPC collector). The results were compared and a good agreement between the steadystate and the quasi-dynamic test results was observed. Issues concerning the incidence angle modifiers and the effective thermal capacity of the collectors were analyzed in detail, which resulted in the identification of model and test limitations. Suggestions are given to improve the test methodology and the data analysis of quasi-dynamic test.

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Abstract. For the development and establishment of concentrating solar thermal collectors a reliable and comparable performance testing and evaluation is of great importance. To ensure a consistent performance testing in the area of lowtemperature collectors a widely accepted and commonly used international testing standard (ISO 9806:2013) is already available. In contrast to this, the standard ISO 9806:2013 has not completely penetrated the testing sector of concentrating collectors yet. On that account a detailed literature review has been performed on published testing procedures and evaluation methodologies as well as existing testing standards. The review summarizes characteristics of the different steady-state, quasi-dynamic and fully dynamic testing methods and presents current advancements, assets and drawbacks as well as limitations of the evaluation procedures. Little research is published in the area of (quasi-) dynamic testing of large solar collectors and fields. As a complementary a survey has been conducted focusing on currently implemented evaluation procedures in this particular field. Among the ten participants of the survey were project partners of relevant industry and research institutions within the European project STAGE-STE (Work package 11 -Linear focusing STE technologies). The survey addressed general aspects of the systems under test, as well as required process conditions and detailed characteristics of the evaluation procedures. In congruence with the literature review, the survey shows a similar tendency: the quasi-dynamic testing method according ISO 9806:2013 presents the most common and advanced evaluation procedure mainly used in the context of tracking concentrating collectors for the performance assessment of parabolic trough collectors operating with thermal oil or pressurized water. These common solar systems can be evaluated with minor adaptions to the testing standard. Evaluation procedures focused on in-situ measurements in solar fields or collectors are scarce and complex as well as an evaluation of linear Fresnel collectors or other systems operating with non-common heat transfer media like molten salt and direct steam. As those are still SolarPACES 2015

Tonatiuh is an open source, freeware, Monte Carlo ray tracer suitable for CST applications, and is currently under further development to to increase and improve its functionalities. Work has recently been performed to implement the following functionalities: a flux distribution calculation utility; materials with incidence angle dependent optical properties; and the ability to import 3D geometries from CAD files. This paper provides a detailed account of these new functionalities, and the tests performed to establish their correct implementation in the new software version, Tonatiuh v 2.2.3.

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