ABSTRACT
The aim of this work is to develop an accurate bridge between short term collector testing and long term collector performance prediction. The method is well suited also for in situ testing of large collector arrays. At the Älvkarleby Laboratory the method is now used as a routine method to evaluate new materials and collector designs. The method has also been tested at the Swedish National testing institute and at ITW in Stuttgart with results showing that the method has a potential also for standardised collector testing.
A standard collector model (compatible with the ISO standard) can be used with the addition of correction terms for beam and diffuse incidence angle modifiers, thermal capacitance, wind speed and śky temperature. The most recent development is a routine that makes it possible to accurately identify the incidence angle dependence of the zero loss efficiency. This widens the application of the method to collectors with special incidence angle effects. A reflector model has also been developed that can handle collectors with external booster mirrors in front.
So far time steps down to 10 minutes has been tested with good results. Standard multiple regression routines available in most spread sheet programs like Lotus, Excel or Symphony can be used for the identification of the model parameters. The process from raw data to a set of parameter values takes a few minutes.
Standard collector test equipment can be used. There is no requirement for stationary conditions during measurements. Data with rapidly changing irradiation and inlet temperature can be used. (Data points at step changes in temperature may have to be sorted out). The basic model parameters can be used directly in simulation programmes as TRNSYS, WATSUN and MINSUN.
