The aim of this Master Thesis work is to optimize the Quasi-Dynamic Test (QDT) method used to evaluate the thermal performance of solar collectors. Three main areas of improvement are identified; increasing the angular resolution in the evaluation process, using a dynamic inlet temperature variation, both to increase the accuracy and the latter in combination with night time measurements to shorten the required test period. These options are tested, on one side with simulated data from TRNSYS, and on the other through experiments on a flat plate collector and a heat pipe evacuated tube collector. The results from analytical testing on simulated collector data show that an increased angular resolution, a dynamic inlet temperature change and night measurements are valid options for improving the QDT method. Experimental trials conducted on one type of flat-plate collector show that increasing the angular resolution in the evaluation is useful for detecting measurement errors caused by external factors and confirm the theoretical findings of using a dynamic inlet temperature variation coupled with night time measurements.