State of the art of performance evaluation methods for concentrating solar collectors
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 low- temperature 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 presenting niche products and testing wise challenging systems under real test conditions a more sophisticated evaluation procedure such as the dynamic testing method is expected to be better suited.