This study investigates the simulation capabilities of eight existing tools for building-integrated photovoltaic (BIPV) energy simulation. The research is based on one existing building project with three different types of BIPV installations. The study aims to assess the ability of these tools in modelling and importing building geometry, selecting weather data, setting system layout and array, evaluating solar resource, estimating energy losses, and assessing energy generation. The study concludes that the selection of weather and solar resource data significantly affects energy forecasting. PV simulation tools vary in their handling of solar resource input data; some operate as a "black box" with limited flexibility, accepting only specific data formats such as TMY or only GHI. Others are more versatile, accepting multiple years of data and different solar irradiance components. During this comparison study, simplifications were necessary to find common ground between the tools, leading to the exclusive use of TMY weather data for simulation and comparison with one year's measured yield. The study was conducted as part of the Technology Collaboration Programme of the International Energy Agency (IEA), which is an autonomous body within the framework of the Organization for Economic Cooperation and Development (OECD). The IEA Photovoltaic Power Systems Programme (PVPS) is one of the Technology Collaboration Programmes established within the International Energy Agency in 1993. The PVPS has 32 members, including 27 countries, the European Commission, and four associations. The programme aims to enhance international collaborative efforts to facilitate the role of photovoltaic solar energy as a cornerstone in the transition to sustainable energy systems.This study investigates the simulation capabilities of eight existing tools for building-integrated photovoltaic (BIPV) energy simulation. The research is based on one existing building project with three different types of BIPV installations. The study aims to assess the ability of these tools in modelling and importing building geometry, selecting weather data, setting system layout and array, evaluating solar resource, estimating energy losses, and assessing energy generation. The study concludes that the selection of weather and solar resource data significantly affects energy forecasting. PV simulation tools vary in their handling of solar resource input data; some operate as a "black box" with limited flexibility, accepting only specific data formats such as TMY or only GHI. Others are more versatile, accepting multiple years of data and different solar irradiance components. During this comparison study, simplifications were necessary to find common ground between the tools, leading to the exclusive use of TMY weather data for simulation and comparison with one year's measured yield. The study was conducted as part of the Technology Collaboration Programme of the International Energy Agency (IEA), which is an autonomous body within the framework of the Organization for Economic Cooperation and Development (OECD). The IEA Photovoltaic Power Systems Programme (PVPS) is one of the Technology Collaboration Programmes established within the International Energy Agency in 1993. The PVPS has 32 members, including 27 countries, the European Commission, and four associations. The programme aims to enhance international collaborative efforts to facilitate the role of photovoltaic solar energy as a cornerstone in the transition to sustainable energy systems.