The recent boom in distributed generation together with decreases in the cost of technology has resulted in photovoltaic energy becoming the most widely used means of producing electricity in buildings. Analysing this technology requires models that use the data available in the manufacturers' catalogues to study energetic and economic impact of the different commercial solutions available. Furthermore, if the model is to be integrated into a complex simultaneous simulation algorithm for different solutions, it should have a low computational cost. The electricity output of photovoltaic modules is characterized by the I-V response according to the ambient temperature. A review of the literature leads to the conclusion that existing models are difficult to parameterize using the data available in the technical product datasheets. This study presents an explicit, simplified model to determine the characteristic I-V curve of photovoltaic modules by means of a direct link with the data available in the catalogues of manufacturers. The model's validity and quality of results it provides have been tested on a sample of 259 modules of different brands, sizes and technologies, as well as under varying operating conditions. The explicit model proposed is highly accurate, easy to reproduce, and can be adapted to the parameters found in most manufacturers' catalogues.