An algorithm for estimating solar energy potential of facades in an urban context is proposed in this paper. The potential is presented in terms of the ratio of direct solar energy accumulated on facades when shadowing effects of nearby buildings are considered and to an ideal scenario when these shadowing effects are ignored. In achieving this, the algorithm utilizes a 1.5D Digital Surface Model (DSM) aligned with lines of latitude. On this basis, it is able to assess daily and year round potential during times when the sun is at solar noon. The algorithm is designed to be easily converted into a computer program. Also, the time and computer memory required for the assessment is independent of the complexity of a given relief. To illustrate the algorithm, three case studies considering hypothetical DSM’s of equal façade surface areas, located in Auckland (New Zealand), are presented and compared with each other.