Investments in renewable energy (RE) technologies are regarded with increasing interest as an effective means to stimulate growth and accelerate the recovery from the recent financial crisis. Yet, despite their appeal, and the numerous policies implemented to promote these technologies, the diffusion of RE projects remains somehow below expectations. This limited penetration is also due to a lack of appropriate financing and to a certain reluctance to invest in these technologies. In order to shed light on this phenomenon, in this paper we examine the decision making process underlying investments in RE technologies. We propose and test a conceptual model that examines the structural and behavioural factors affecting the investors decisions as well as the relationship between RE investments and portfolio performance. Applying econometric techniques on primary data collected from a sample of European investors, we study how the investors' a-priori beliefs, their preferences over policy instruments and their attitude toward technological risk affect the likelihood of investing in RE projects. We also demonstrate that portfolio performance increases with an increase of the RE share in the portfolio. Implications for scholars, investors, technology managers and policy makers are derived and discussed. (C) 2010 Elsevier Ltd. All rights reserved.