A comparison of three test methods for determining the thermal performance of parabolic trough solar collectors

•Three outdoor test methods for parabolic trough solar collectors were compared.•Four typical tests were conducted at transient working conditions for the regression.•The regressed parameters of mathematical models in the test methods were analyzed.•The comparative analysis on thermal performance predictions was carried out. Based on the theoretical background and experimental results, a study on the extensive comparison of three outdoor test methods for determining the thermal performance of parabolic trough solar collectors is presented. These test methods are the steady-state method in the ASHRAE 93 standard, the quasi-dynamic method in the EN 12975-2 standard and a new dynamic method developed by Xu et al. They are discussed in detail and are explained in view of the on-site parabolic trough solar collectors in the real service. In addition, the experimental data acquired from four typical test cases at the transient working conditions is applied to obtain the parameters of three mathematical models in the test methods and predict the collector outlet temperature, and collector output power. Furthermore, the comparative analysis on the projections of the essential thermal performance indicators shows the advantages and disadvantages of these three test models according to both the practical operation and weather conditions, which proves that the dynamic model may be the potential core of a quick, reliable on-site thermal performance test method at some future time.