This paper studies the knowledge spillovers generated by renewable energy technologies, unraveling the technological fields that benefit from knowledge developed in storage, solar, wind, marine, hydropower, geothermal, waste and biomass energy technologies. Using citation data of patents in renewable technologies at 17 European countries over the 1978-2006 period, the analysis examines the relative importance of knowledge flows within the same specific technological field (intra-technology spillovers), to other technologies in the field of power-generation (inter technology spillovers), and to technologies unrelated to power-generation (external-technology spillovers). The results show significant differences across various renewable technologies. While wind technologies mainly find applications within their own technological field, a large share of innovations in solar energy and storage technologies find applications outside the field of power generation, suggesting that solar technologies are more general and, therefore, may have a higher value for society. Finally, the knowledge from waste and biomass technologies is mainly exploited by fossil-fuel power-generating technologies. The paper discusses the implications of these results for the design of R&D policies for renewable energy innovation.