On the choice of the parameter identification procedure in quasi-dynamic testing of low-temperature solar collectors

The ISO 9806:2017 standard is widely used to characterize the thermal performance of solar collectors. It permits two test methods: Steady State Testing (SST) and Quasi-Dynamic Testing (QDT). While SST requires high stability and clear sky conditions, which limit its application, QDT offers more flexibility in sky conditions. In contrast, the QDT method adds complexity due to the handling of transient phenomena during data processing. There are two approaches to parameter identification in QDT: multilinear regression (MLR) and dynamic parameter identification (DPI). MLR, the most common tool, faces challenges with certain collector types and its results depend on the data averaging time. DPI, while more complex, has the potential to overcome MLR’s shortcomings. Which of these two methods is most suitable for testing low-temperature solar collectors in a broad sense is an issue that has not yet been addressed. This work provides evidence that the DPI procedure is more convenient than the MLR procedure, especially for evacuated tube collectors with heat pipes. Specifically, it is shown that DPI produces more reliable test results and provides more accurate estimates of useful power, and it exhibits less variability with respect to data averaging time, demonstrating its improved robustness.