Solar radiation in the urban fabric

Three-dimensional urban geometry makes incident solar radiation vary across many spatial and temporal scales at once. Describing that variability compactly is a hard and useful problem.

In an open field, the solar resource is close to a single time series. In a city it is a four-dimensional field: every façade and every roof sees a different sky, shaded by different neighbours at different hours, and the whole pattern turns with the seasons.

This work characterises that variability and looks for compact ways to represent it. Principal component analysis, proper orthogonal decomposition and higher-order (multilinear) decompositions are used to separate the spatial and temporal structures of the urban radiation field, so that a small number of modes can stand in for an expensive full simulation. Alongside this, simulation tools for façade irradiation have been compared against each other and validated, because a model that nobody has checked is not a model anyone should plan with.