# Modeling Photovoltaic Potential for Bus Shelters on a City-Scale: A Case Study in Lisbon
## 3 Results and Discussion
### Spatial Planning Scenarios  
The 612 solar bus shelters were further investigated according to social criteria (tourists and daily commuters). There are no data on the number of users at each stop, so proxies were used to describe this phenomenon. Proximity analysis was applied to select the bus shelters according to their estimated use. Generally, in the public transit industry, buffers at 400 m around bus stops and 800 m around rail stations are commonly used to identify the areas from which most transit users will access the system by foot [30].  
To characterize the tourist use, all the high insolation shelters that served sightseeing tours or that were within 800 m of monuments, museums and viewpoints were identified. For characterizing the commuter use, the bus shelters within 400 m of schools (basic, secondary and high), health care facilities (hospitals and medical centers), and metro and train stations were selected. The rationale was that tourists are more willing to walk longer distances than daily commuters. For each category, the georeferenced information available at the city hall was used.  
According to the proximity analysis of the 612 solar bus shelters, 551 are within the proxy distance, detailed above. From this, 374 are used by tourists and 510, by the city's commuters. Among these, 333 served both tourists and city commuters (Table 3) (Figure 11).  
Planning for solar innovative solutions requires knowledge about not only the local energy production capabilities but also the existence of local demand and where it occurs in the city. The goal is to match the city's geographical and technical potential with its social one. To support decision-makers regarding implementation strategies, several planning scenarios were produced based on the PV-based applications and the respective target audience. Based on (1) the bus shelter locations used by the tourists and the daily commuters and (2) the spatial distribution of bus shelters with typified PV applications, three planning scenarios were produced (Table 4). As anticipated, being higher in number, the bus shelters used by commuters would be suitable for more PV applications and more lighting power than those used by tourists. Nevertheless, half of the locations (308) served both uses and could offer small-scale info displays, ticket machines or refrigerated vending machines, and 21% (128) could be equipped with 10 W/m\({}^{2}\) LED lamps.  
The tourist use pattern follows the cultural attraction sites, being more concentrated on the riverside, while the daily use is dispersed throughout the city (Figure 12).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Users of Solar Bus Shelters**} \\ \cline{3-5}  & & **Tourists** & **Commuters** & **Tourists and Commuters** \\ \hline \multirow{4}{*}{PV applications} & L1 + L2: & & \\  & Remote small-scale sensors/small & 261 & 359 & 231 \\  & scale info display up to 20\({}^{7}\) & & & \\ \cline{2-5}  & L1 + L3: & & & \\  & Remote small-scale & 92 & 128 & 81 \\  & sensors/ticket machine & & & \\ \cline{2-5}  & L1 + L4: & & & \\  & Remote small-scale & 21 & 23 & 14 \\  & sensors/refrigerated vending machine & & & \\ \hline PV illumination & 10 W/m\({}^{2}\) LED lamps & 144 & 197 & 128 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Solar bus shelters scenarios based on the PV capability and the estimated use.  
Figure 11: Solar bus shelter locations according to tourist and commuter use (**a**), and close-up view of a neighborhood (**b**).  
The results indicate that 612 bus shelters have the potential to be improved. This constitutes an opportunity for providing a better experience to commuters and tourists while improving the quality of the public space. Furthermore, through renovation, Solar bus shelters can create value for businesses and public transport providers.