It is well known that the electrical characterisation of a module under standard test conditions (STC) is not sufficient to explain differences in the final energy output. To be able to predict the energy of a module one needs more input information, which can be either determined through indoor and/or outdoor tests. With still no standard energy rating (ER) measurement procedure available, different methods were here compared to each other with the aim of identifying the one which leads to the best energy predictions, with the highest repeatability and in the shortest time. The most straightforward method was then used to predict the energy of the 14 different module types measured within the last module performance inter-comparison run by ISAAC. The energy rating prediction tool used therefore is the Matrix Method developed by ISAAC. The accuracy of the final energy prediction is presented and discussed.