This article presents the development of a numerical model coupling the thermal and biological behaviors of a microalgae biofaçade. Heat fluxes and illumination are modulated by actual weather data, and the system response is evaluated in terms of biomass and pigment production. First, the effect of the different model refinements are screened. Then, the model is applied to an illustrative case: the city of Marseille over the year 2023. The results illustrate the model's capabilities, such as assessing the building/biofaçade thermal synergy or the summer/winter operational differences. The numerical behavior of the model is also analyzed: local and global sensitivity analyses assess the impact of uncertain parameters. The parameter inducing the highest amount of uncertainty is the microalgae photoconversion efficiency, highlighting the need to ascertain its value before designing a system. Despite this uncertainty, even under conservative assumptions, the predictions of the model are 10 % accurate.