This chapter presents a bibliometric study identifying clusters (cities) that are ‘champions’ in acceleration of invention in solar photovoltaics (PV), using patent analysis. The number of inventions has increased rapidly in the past decades, particularly since 2003. In this process, leading clusters change, in part, over time. Some have held their position since 2000 – Tokyo, Osaka, Seoul and Taipei in East Asia, and San Jose in the US – whereas most high-performing clusters in the US have somewhat lost their position, for example Los Angeles. Over time, there is an increased spread of inventive performance in PV technology across the world. To improve understanding of these patterns, a regression model has been estimated. Using data from 110 clusters, it appears that agglomeration factors and relational factors are equally influential, and they also tend to reinforce each other. Leadership tends to follow from a delicate balance between the size of the cluster and size/diversity of its networks.