The purpose of this work is to present a comparison between two standardized test methods for the evaluation of the energy performance of Solar Domestic Hot Water (SDHW) systems. The approaches investigated concern the Dynamic method (DST) and the Input-Output method (CSTG). These methods have been officially established as ISO standards, thus they have found wide dissemination, and their results are supposed to be equivalent to one another. A description of the operation principle of each method and the corresponding test procedures is presented, focusing on the aspects related to the practical implementation of these methods on a laboratory level. A Solar Domestic Hot Water system is tested according to both methods. On the basis of the measurements, the characteristic parameters of the SDHW system are calculated for each method and the long-term performance under typical meteorological conditions is estimated. Consequently, a comparative evaluation and analysis of the observed deviations between the results of the two methods are performed. Besides the quantitative comparison, this work has attempted to evaluate the two methods on a qualitative basis as well, by focusing on their functionality, their requirements regarding the number of test days considered and the physical interpretation of the results. (C) 2009 Elsevier Ltd. All rights reserved.