Modelling the overall efficiency of parabolic trough collectors

In the present study, optical and thermal modelling is applied with the aim to contribute to the identification of the proper form of the overall performance equation of Parabolic Trough Collectors (PTC). Numerical experiments are performed for a range of operational parameter values that refer to medium temperatures. The computational data are used for assessing the capability of existing and new forms of the characteristic equation to better correlate the overall efficiency. Parameters under consideration include the end-loss factor, the Incidence-Angle Modifier (IAM) and the thermal losses. Results indicate that IAM models affect the correlation of the optical performance. Regarding thermal losses, a new model is proposed. It involves a term representing the radiation flux to the ambient, as dictated by the corresponding transport mechanism. Since thermal losses comprise a small amount of the incident flux to the receiver, the corresponding terms slightly affects the correlation of the overall performance, which is shown to be affected more by IAM modelling. The comparison between IAM models indicates that a correlation based on a second-order polynomial function of the incidence angle, even though leading to comparable correlation coefficients values, produces one order of magnitude lower standard deviation of the sample.