Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener Efficient time-resolved 3D solar potential modelling Christoph Waibel a,b, ⁎ , Ralph Evins b,c , Jan Carmeliet a,d a Chair of Building Physics, Department of Mechanical and Process Engineering, Swiss Federal Institute of Technology in Zurich (ETH Zurich), Stefano-Franscini-Platz 1, 8093 Zurich, Switzerland b Urban Energy Systems Laboratory, Swiss Federal Laboratories for Materials Science and Technology (Empa), Überlandstrasse 129, 8600 Dübendorf, Switzerland c Sustainable Cities and Energy Systems Group, Department of Civil Engineering, University of Victoria, 3800 Finnerty Rd, Victoria V8P 5C2, British Columbia, Canada d Laboratory for Multi-Scale Studies in Building Physics, Swiss Federal Laboratories for Materials Science and Technology (Empa), Überlandstrasse 129, 8600 Dübendorf, Switzerland ARTICLE INFO Keywords: Solar potential model Vegetation model Parametric study Interpolation ABSTRACT This study presents an efficient model for the calculation of 3-dimensional time-resolved solar potentials, based on the Perez solar model. The new model features a novel interpolation scheme for the generation of annual hourly time-series, diffuse and specular inter-reflection, a multi-layer approach to model the attenuation of solar radiation through vegetation, and snow-coverage. It is fully integrated in a 3D CAD environment to facilitate its application. Extensive validation case studies prove the high match of the new model to three other well-es- tablished programs: Radiance, Daysim and EnergyPlus. A thorough analysis of the effect of various model parameter settings highlights the importance of assessing site specific characteristics and modelling uncertainty caused by parameter selection. Our results show a significant reduction in computing times compared to Daysim and EnergyPlus, while generating less mismatches in geometric obstruction calculations when assuming Radiance as a reference. Furthermore, the considered case studies suggest that modelling the shading effect of vegetation is indispensable in solar potential analyses and should not be neglected. 1. Introduction 1.1. Motivation Integrating solar technologies into urban environments is an es- sential step for a transformation towards renewable and sustainable cities (International Energy Agency, 2016). While there exist a number of models for the evaluation of solar potentials on rooftops and façades, the necessary computing times impede frequent use of such tools during the design phase of buildings and districts. Particularly urban morphologies and building forms can have a major impact on the fea- sibility of solar technologies (Takebayashi et al., 2015; Chatzipoulka et al., 2016; Martins et al., 2016; Mohajeri et al., 2016; Lobaccaro et al., 2017). Hence it is imperative to make the evaluation of solar potentials an integral part of the conceptual design of cities. A faster simulation method may facilitate this, as it reduces the time cost of solar simula- tions and lowers the barriers to their application in intuitive design and computational optimisation (Attia et al., 2013). In particular sampling- based optimisation may require excessive use of the simulator, totalling hundreds or thousands of simulations (Evins, 2013). Another aspect is the importance of solar technologies in decen- tralised multi-energy systems, where the transmission, transformation and storage of different carriers is considered within the same frame- work to optimally meet energy demands (Allegrini et al., 2015). A re- cent study demonstrated the impact of urban and building form on such multi-energy systems (Waibel et al., 2016). In summary, (i) solar technologies in cities play a crucial role for a sustainable energy future, (ii) urban and building design significantly impacts solar potentials, and (iii) the faster a design proposal can be evaluated according to its solar potentials, the more efficiently can such simulations be applied during intuitive design and computational op- timisation. 1.2. Review on urban solar potential modelling Numerous solar models and programs have been published for various purposes, ranging from meteorological to micro scale. Robinson and Stone (2004) describes modelling techniques for obstructed surface irradiation in the urban context. Freitas et al. (2015) provides a review of a range of solar radiation methods suited to urban environments. The authors conclude by listing current limitations, including a lack of http://dx.doi.org/10.1016/j.solener.2017.10.054 Received 13 September 2017; Received in revised form 14 October 2017; Accepted 17 October 2017 ⁎ Corresponding author at: Chair of Building Physics, Department of Mechanical and Process Engineering, Swiss Federal Institute of Technology in Zurich (ETH Zurich), Stefano- Franscini-Platz 1, 8093 Zurich, Switzerland. E-mail addresses: chwaibel@student.ethz.ch (C. Waibel), revins@uvic.ca (R. Evins), cajan@ethz.ch (J. Carmeliet). Solar Energy 158 (2017) 960–976 Available online 05 November 2017 0038-092X/ © 2017 Elsevier Ltd. All rights reserved. T