# Photovoltaic Roundabouts for Enhancement of Self-Sufficiency and Resiliency
## 4 Conclusions  
The most important result of this study is the possibility of evaluating the level of self-consumption by considering different configurations associated with the combination of different crucial variables such as: annual irradiation, annual demand, photovoltaic technology and diameter of the roundabout. The most interesting output of this analysis is the \"critical diameter\" of the roundabout, with which 100% self-consumption can be achieved for each case studied. The self-consumption represents the starting point for energy self-sufficiency, specifically it is the theoretical upper value. Therefore, it can be said that the roundabout whose inscribed diameter coincides with the critical diameter could potentially achieve self-consumption. The quantitative results reported in this paper are based on the assumed efficiency of the two PV technologies used. Moreover, the annual analysis based on hourly simulations based on long-term meteorological data (global irradiance, ambient temperature, wind speed) is justified by the consideration that the PV system is connected to the grid. The bifacial PV modules that have just entered the market, which convert sunlight into DC electricity on both the front and back sides of the PV modules (and which can be used with either a fixed or tracking structure), can significantly increase annual production depending on the ratio between diffuse and global solar radiation. This means that roundabouts with smaller diameters can also be used to supply local loads. Moreover, the results reported in this paper refer to the typical values of irradiance and lighting demand in the Mediterranean region, whereas towards the north the annual PV production decreases and the demand increases. To extend the use of roundabouts to such locations, it is necessary to increase the area performance and energy density of PV systems. The bifacial modules are very effective in the Northern countries, where the diffuse component of the radiation is high, and the optimal tilt angle is larger than in the Southern countries. On the other hand, the presence of lighting poles (central pole or perimetral poles) can lead to shading patterns that negatively affect the electrical energy production of RAPS systems. Additionally, in this case, there is a technological solution based on the idea of Distributed Maximum Power Point Tracking (DMPPT) techniques. It allows each photovoltaic module in a system to operate at its Maximum Power Point. This is highly desirable from an efficiency point of view when operating conditions do not match. As for the larger roundabouts, the surplus from production could be used to provide charging stations for electric vehicles. Finally, it should be noted that the level of mismatch between the energy demand of the roundabout and the photovoltaic generation profile is very large, so a storage system is required to achieve a good degree of self-sufficiency. Only in this context, among others, the variability of weather conditions during the year is a crucial information. However, a further distinction should be made as the storage system can be considered as a grid-connected or stand-alone system. Since roundabout lighting plays an important role in safety, a grid-connected system can provide a high degree of reliability in powering roundabout lighting. The optimal technical and economic sizing of the storage system is beyond the scope of this paper, but is certainly one of the further developments of this research. Conceptualization, S.L., G.M.T. and N.D.; methodology, S.L., G.M.T. and N.D.; software, S.L. and N.D.; validation, G.M.T. ; formal analysis, N.D.; investigation, S.L. ; resources, S.L. and G.M.T. ; data curation, N.D.; writing--original draft preparation, N.D.; writing--review and editing, S.L., N.D. and G.M.T. ; visualization, N.D.; supervision, G.M.T. ; project administration, S.L. and G.M.T. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable.