Photovoltaic (PV) systems are critical for renewable energy expansion, potentially surpassing hydropower as the number one renewable energy source globally by 2029. However, accurate PV performance modeling in high latitudes remains challenging due to unique climatic conditions and solar irradiance variability. This thesis addresses these challenges by assessing the accuracy of PV power prediction in the building energy simulation software IDA ICE and investigating the “inverse problem”, Global Tilted Irradiance (GTI) reverse transposition and separation. Two studies were conducted and are presented in this thesis: (1) a validation of IDA ICE simulations using data from two BAPV and one BIPV system, measured in Borås, Sweden, (latitude 57.7) and (2) an evaluation of GTI reverse transposition and separation models, based on data measured in Glava, Sweden, (latitude 59.5). Results show that PV simulation integrated in the IDA ICE whole building energy models is comparably accurate to that of stand-alone PV design tools, though further studies are needed to evaluate performance under shading conditions and for simulation of colored PV. Furthermore, two suitable GTI reverse transposition and separation models were identified for application at high latitudes. These were the proposed optimization model with ENGERER2 and HAY & DAVIES transposition and the established PEREZ-DRIESSE model.