Urban areas are facing a growing deployment of solar technologies on the built exposed surfaces such as roofs and façades. This transformation often occurs without consideration of the needed architectural quality, which depends on the context sensitivity and on solar technologies visibility from public space. The definition of visibility is explored in this paper, and major assessment methods are described. Specifically, a Cumulative Viewshed Algorithm (CVS) is compared with a novel backward raytracing Illuminance Metric Approach (ILL). Results from a test-case in Geneva show how CVS better describes visibility from a remote perspective, while ILL is a promising and fast method for closer viewpoints, especially in urban canyon environments.