What socio-technical regimes foster solar energy champions? Analysing uneven photovoltaic diffusion at a subnational level in Switzerland

Transitioning to cleaner modes of electricity production requires a major uptake of renewable technologies, including solar photovoltaic (PV). However, the uptake has been spatially uneven within countries and requires more exploration. We analyse the spatial pattern of solar PV growth in Switzerland (76′587 PV projects) by quantifying the features of socio-technical regimes at a subnational level. We combine the multi-level perspective (MLP) framework with the literature on solar PV adoption to select 36 quantitative indicators at the level of 2′212 municipalities. Using principal component analysis and cluster analysis, each municipality's socio- technical regime is quantitatively assessed and municipalities with similar regime features are clustered together. We find nine clusters of municipalities with different socio-technical regimes and different rates of solar PV uptake. Specifically, solar PV uptake is greater in clusters with more prevalent techno-scientific knowledge and market dimensions of the MLP, in particular agricultural activities, higher education institutions, and innovation activities. Within each cluster, we identify extreme outliers (i.e. municipalities where solar PV is growing much faster) and further analyse them through a comprehensive Internet search. Our results suggest that, given the same national policy, different local actors, such as local authorities, energy companies, and devoted citizens, can accelerate PV uptake using various strategies based on local specificities. Building on these findings, we suggest that knowledge of regime configurations may provide additional tools to create context- specific strategies and more decentralized transformative policies to foster solar PV uptake