# Numerical Validation of the Radiative Model for the Solar Cadaster Developed for Greater Geneva
## 1 Introduction  
The massive use of renewable energies and, more particularly, solar energy is necessary in order to meet the objectives of the Paris Agreements and the Swiss federal law on the reduction of greenhouse gas emissions (CO\({}_{2}\) law) [1]. As buildings are some of the main contributors to climate change, one of the main challenges is, therefore, turning buildings from energy consumers into energy producers. This cannot be done without the development of tools dedicated to the evaluation of solar potential.  
This massive deployment involves the evaluation of solar potential on a large scale. In addition, the urban environment has many specific features that are to be taken into consideration when evaluating this potential. This can be achieved with solar cadasters.  
However, these tools are usually limited to the evaluation of the solar potential on rooftops [2, 3, 4, 5]. This limitation can be an obstacle to the development of the use of solar energy because the potential of vertical surfaces in an urban environment can prove to be predominant [6, 7, 8, 9].  
Thus, there is a need for large-scale tools that are able to take vertical facades into account, in addition to roofs. From a physical point of view, the effects of surroundingsurfaces (the ground or surrounding buildings) on the vertical radiative balance are not well known and may appear to be non-negligible. From the point of view of solar production potential, the issues of the variability linked to shading effects are added. Tools that are able to consider these issues are being developed and need validation.  
A solar cadaster tool is being developed at the scale of Greater Geneva, which is a trans-border agglomeration around the city of Geneva between France and Switzerland, and it totals an area of 2000 km\({}^{2}\). A first solar cadaster was developed for the Canton of Geneva only (280 km\({}^{2}\)), as presented by [PERSON] et al. (2010). The goal now is to update and extend this solar cadaster for the whole of the Greater Geneva area in the framework of INTERREG G2 Solar. Its aim is to intensify solar energy production in the agglomeration by mobilizing a large panel of stakeholders from public institutions, municipalities, energy providers, the private sector, and universities. The difficulty lies in the fact that the solar cadaster must cover a large area (2000 km\({}^{2}\) for Greater Geneva) while providing accurate information at a small spatial resolution and with a reasonable computation time.  
The main objective of this study is to validate a solar cadaster tool by using a comparison with the results from other numerical tools. To this purpose, the results from the solar cadaster are compared with those of two widely used tools: DIVA-for-Rhino and ENVI-met. The latter, thanks to its holistic model, makes it possible to deepen the assessment of the buildings' photovoltaic potential by evaluating their surface temperatures.  
The validation of the solar cadaster involves three different tools based on different models and methods and with a varied field of applications. Thus, these tools are presented first, prior to introducing the methodology used. The results in terms of predicted shortwave irradiance on both the roofs and the facades are then detailed and discussed.