Experiences and lessons learned from 30 years of dynamic collector testing, modelling and simulation

Dynamic testing and modeling (in contrast to Steady State line of action) of solar collectors is to prefer in most climates, except for the most extreme locations with clear skies every day. A very important part of dynamic testing and modeling is not only the thermal capacitance correction, but also the split of the solar radiation absorption modeling, into beam and diffuse and the modeling of the collectors’ incidence angle dependency for both beam and diffuse radiation.

These optical features are in most situations more important than the accuracy of the dynamic and thermal loss part of the model. This can be seen from the statistical analyze when evaluating test data. The t-ratios i.e. the parameter values divided by their standard deviations, are generally much higher (often 10 times higher) for the optical parameters than for the thermal loss ones.

There are also important details concerning solar radiation measurements for beam and diffuse including alignment of sensors and test object, that are often not considered, which will be discussed and lessons learned will be given. A misalignment of just a few degrees of the collector test stand or the solar sensors will immediately show up in a dynamic test evaluation, especially when analyzing the incidence angle modifier behavior and thermal capacitance of a collector.

To achieve good results in dynamic testing it is essential to understand the basic concepts of the method and to use this understanding when designing a test rig and collecting data during a test for later analyze. It is very desirable to use a continuous parameter feedback during the test, so that the test conditions can be changed hour by hour to derive more accurate results and shorten the testing time.

Such advice will be discussed in the paper. Some of these findings has not yet reached the EN12975 standard level, and suggestions for revisions and improvements will be presented that have general application also for non standardized testing, for example research and development testing.