# Modeling Photovoltaic Potential for Bus Shelters on a City-Scale: A Case Study in Lisbon
## 1 Introduction
### State of the Art  
Not all locations in the city are suitable for solar panels. Thus, decision-makers and planners must decide where to promote PV-based urban solutions using realistic scenarios based on local potential [10]. There is already a significant amount of literature addressing the solar potential of building rooftops and facades [11]. However, the estimation of the PV potential of non-conventional urban surfaces is a novel field of investigation. The authors in [12; 13] analyzed the solar potential of streets for intelligent urban furniture and services that require powering. The proposed methodology could measure the solar energy exposure of a flat surface at any height above the street level within the unoccupied volume of an urban environment. The method was used by [14] to evaluate the viability of installing solar street lights. The results obtained for a Lisbon neighborhood showed that 50% of the existing street lights could be powered by solar panels.  
The authors in [15] performed a feasibility analysis, using solar irradiation maps, to identify suitable areas in Turin, Italy, for the installation of PV modules on top of public transport shelters. The tested prototype, designed to offer a Wi-Fi connection, two USB chargers and an air pollution control system, could be implemented in 43% of the available locations, according to a minimum cover of the electrical load.  
The authors in [16] suggested a GIS-based model for locating PV charging stations in Beijing, China. Several evaluation criteria for the location of PV charging stations were tested: natural (including solar radiation), economic, technical and social factors. The results show that social factors and future expandable potential are more significant when planning the PV layout.  
In this work, we take one step forward by addressing the solar potential of common urban structures in the public space, considering other criteria rather than solely the solar potential. Using bus shelters as a case study, a framework is proposed to match the best solar production sites with the  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**City, Country** & **PV-Based Solutions** & **Reference** \\ \hline Vancouver, Canada & Lighting & [4] \\ Tucson, USA & Lighting & [5] \\ Seattle, USA & Lighting & [5] \\ London, England & Lighting and informative displays & [6] \\ Paris, France & Informative displays & [7] \\ San Francisco, USA & Lighting and informative displays & [8] \\ Singapore, China & Mobile charge & [9] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Cities with pilot solar-powered bus shelters.  
local energy demand. This is done by (1) evaluating the solar potential of all bus shelters within a city, according to geographical and technical criteria, and then (2) selecting the best locations for implementation according to social criteria (e.g., tourist and commuter use) as a proxy for local energy demand. This framework can be applied to any PV-based urban solution in the public space, from street lighting to charging stations for mobile devices or e-bikes, or to informative multimedia stands.  
The remainder of the article is organized as follows. In the next section, Section 2, the study area, the materials and the methodology for assessing a city's potential for PV-based urban applications are presented. Section 3 outlines how the methodology was tested in Lisbon, Portugal, and the results are discussed; the city's potential for solar bus shelters is evaluated according to geographical, technical and social criteria and presented in a set of alternative planning scenarios. In the final part of the article, Section 4, conclusions are drawn based on the achievements and limitations of the proposed approach, and directions for future research are pointed out.