Comparison of two different (quasi-) dynamic testing methods for the performance evaluation of a linear fresnel process heat collector

A small-scale Linear Fresnel Collector (LFC) for the generation of process heat has been tested by Fraunhofer ISE; its performance was evaluated by means of two different methods. The first is a quasi-dynamic testing method performed according to the testing standard ISO 9806: 2013, with modifications in the model to accurately describe LFCs. Due to the two-dimensional Incidence Angle Modifier (IAM) of an LFC, an iterative multi-linear regression (MLR) approach has been developed to be able to comprehensively evaluate the optical performance. The second method is a dynamic testing method based on a parameter identification incorporating a multi-node/plug-flow collector model without strict restraints on mass flow and inlet temperature stability. Both methods are briefly described in their conceptual design and their basic requirements, revealing their similarities and differences. Each method is then applied to real measurement data from an LFC, assessing practicability and identification accuracy. For both methods, the mean absolute difference between identified IAM values and results from ray tracing fell in a range of 0.013-0.017, leading to a similar accuracy in LFC performance evaluation. Differences in optical efficiency between the two methods are smaller, with an average absolute difference below 0.0098, even when using different measurement data and simulation models. Thus the dynamic method represents a good starting point for the further development of an alternative dynamic testing and evaluation method with more flexibility than the current testing standard. This will be significant when evaluating large-scale concentrating collectors and collectors with direct steam generation.