Fine characterisation of the solar resource variability in intricate urban environments by means of higher-order modal decomposition

Helped by the renewable and abundant nature of sun radiation, the production of solar energy on the urban scale forms a core strategy towards more sustainable territories. The morphological variety of three-dimensional structures and radiative diversity of encountered materials yet cause unwanted variations in the solar radiative flux density received by a specific urban region across a wide range of spatiotemporal scales.

The present work uses higher-order modal decomposition to uncover dominant morphological and radiative features on the variability of urban irradiance. The study is conducted on a set of mid-high latitude districts defined as heterogeneous aggregates of cuboid buildings, with differing typological indicators and surface materials. For each geometry, the annual shortwave radiative flux density on all building faces is obtained with a backwards Monte-Carlo method under clear sky conditions. The latter is then arranged as an N-way tensor on the basis of its a priori known space-time characteristics. A Tucker approach is adopted to decompose each tensor field along its dominant patterns of variation via Higher-Order Singular Value Decomposition (HOSVD).

Results prove the benefits of higher-order modal decomposition for providing a rapid and detailed analysis of the solar resource variability in intricate built areas. Dominant modes of variation along individual ways (e.g. space, day of the year, time of the day) are extracted and ranked by order of influence, helping the identification of any variability-prone intra-urban region throughout the year. Information about daily and annual periods of high irradiance variability is obtained, and related changes in its spatial distribution are educed. Variations in the diffuse radiation component and shadows casted by the blocking of direct sun beams from adjacent obstacles are further portrayed. Disruption of light propagation by prominent geometries and highly-specular materials is especially depicted.

Article

PDF : download