Models of the heat dynamics of solar collectors for performance testing

The need for fast and accurate performance testing of solar collectors is increasing. This paper describes a new technique for performance testing which is based on non-linear continuous time models of the heat dynamics of the collector. It is shown that all important performance parameters can be accurately estimated with measurements from a single day.

The estimated parameters are compared with results from standardized test methods (Fischer et al., 2004). Modelling the dynamics of the collector is carried out using stochastic differential equations, which is a well proven efficient method to obtain accurate estimates of parameters in physical models.

The applied method is described by Kristensen et al. (2004) and implemented in the software CTSM1. Examples of successful applications of the method includes modelling the of the heat dynamics of integrated photo-voltaic modules (Friling et al., 2009) and modelling of the heat dynamics of buildings (Madsen and Holst, 1995).

Measurements obtained at a test site in Denmark during the spring 2010 are used for the modelling. The tested collector is a single glazed large area flat plate collector with selective absorber and Teflon anti convection layer. The test rig is described in Fan et al. (2009). The modelling technique provides uncertainty estimates such as confidence intervals for the parameters, and furthermore enables statistical validation of the results.

Such tests can also facilitate procedures for selecting the best model to use, which is a very non-trivial task.