Photovoltaic (PV) system yield prediction models are an important topic in the field of PV solar energy. An accurate prediction model could not only be used for optimising the PV system design, but is also expected to realise the yield potential of innovative PV technologies. In the next generation of PV technologies, one of the most promising concepts is the tandem solar cells. In recent years, these cells have impressed the solar industry by their rapid growth of the maximum power conversion efficiency (PCE). Since tandem solar cells are still at the lab phase, their yield potential under realistic conditions are an interesting field of study as well. However, the existing yield prediction models are not yet available for these tandem cells. In order to fill this gap, a prediction model developed in the Photovoltaic Materials and Devices (PVMD) group of TU Delft, called the PVMD Toolbox, has been adapted to be compatible with the tandem solar cells. In this thesis project, the version 3 of the Toolbox was developed. First the PVMD Toolbox was improved. Except monofacial c-Si cells and bifacial c-Si cell, it is now also available for tandem cells. One of the most promising tandem concepts, the perovskite/c-Si tandem, was taken as a reference tandem configuration integrated in the Toolbox. The Toolbox was also modified to take the influence of solar spectra into consideration and analyses cell performances individually. Secondly, the accuracy of the Toolbox was validated. A new figure of merit called 'relative total deviation' is put forward in this report, which calculates the ratio between the sum of deviations that each simulation introduces, and the total measured energy yield. When the electrical parameters were taken from the own measurements, the relative total deviation of simulation results was only 8.6%. Finally, the Toolbox was applied to two case studies. In the first study, it was found that the annual energy yield (AEY) of perovskite tandems can be increased up to 0.4% by optimising perovskite thickness for a certain location. The second case study compared the AEY of the tandem module and conventional c-Si module. Perovskite tandem module showed a high AEY, around 36% higher than that of the c-Si module. However, perovskite tandem had a lower specific yield as they are more sensitive to the spectral variation