Community renewable energy initiatives are increasingly recognized as important actors to trigger citizen investments in renewable energy facilities. Little is known, however, about the factors that determine the size of financial investments made by community renewable energy members. To address this gap, this paper presents a multivariate econometric analysis of the economic, social, environmental and institutional determinants of the size of investments in community renewable energy. It relies on a large-scale survey of 4061 members of two renewable energy cooperatives located in Flanders, in the northern part of Belgium. Results show that the return on investment is the most important determinant for members of large communities of interest, while environmental, social and other non-economic drivers tend to dominate financial motives for members of smaller communities of place. The presence of other cooperative members in close social networks plays a particularly important role in the latter kind of communities, highlighting the strength of social interactions as a driver for investments. These results can help policy-makers to design more adapted policy measures for fostering financial investments at the community level, and project developers to tailor segmented communication strategies about the goals and benefits of projects.