The development and utilization of solar power has become one of the main strategies to address the energy deficit in the 21st century. Japan has set the promotion of solar power as the nation's new growth target for the next 10 years. This study investigated the inter-correlations between a city's penetration level of residential solar power systems (RSPS) and wide-range indexes that, in this article, are divided into three categories: (1) natural factors, (2) social factors and (3) economic factors. From over 200 Japanese cities, the study randomly selected 35 sample cities with population sizes of 50,000 to 150,000. First, through correlation testing, 22 factors closely related to the city's penetration level of RSPS were extracted. Second, through a principal component analysis, the 22 factors were grouped into 6 components to explain the penetration level of RSPS. The sample cities were further divided into groups by cluster analysis based on the six components for further assessment of the group with a high penetration level. The discussion and conclusions are expected to help companies and governments enhance RSPS development. JEL Classification: C8, Q4, R5