The overall purpose of this thesis is to investigate the determinants of technological change in the renewable energy sector, with a special emphasis on the role of knowledge spillovers and convergence across countries. The thesis consists of a preface and five self-contained papers. In Paper I technological change is broken down into the three major development stages laid out by Joseph Schumpeter: invention, innovation and diffusion. Econometric models of each of these stages are specified in the empirical context of wind power. The models are estimated employing a panel dataset consisting of eight western European countries over the time period 1991-2008. The results display evidence of national and international knowledge spillovers in the invention (i.e., patenting) model. The results from the technology learning models indicate evidence of global learning-by-doing, and that the prices of input factors have been important determinants of wind power costs. In line with previous research, the diffusion model results show that investment costs have influenced the development of installed wind power capacity. Paper II investigates how wind power inventions in European countries have affected the technological development achievements in neighboring countries. Data on the number of patents granted at the European Patent Office (EPO) during the period 1978-2008 in the eight technologically leading wind power countries in Europe are employed in a patent production function framework. The presence of international knowledge spillovers is found to constitute a statistically significant determinant of a country’s patent production. Geographical distance is also taken into consideration, and the results suggest that knowledge spillovers are subject to spatial transaction costs: with longer distances the role of international spillovers becomes weaker. Paper III investigates the convergence of inventive capabilities in the EU. Data on total patents per capita in 13 EU countries over the period 1990-2011 are analyzed using both parametric and non-parametric techniques. Converging inventive abilities may be important for the future of the EU given that rapid technological change has resulted in major structural changes in the Member States’ economies during the last decades. The β-convergence and σ-convergence tests suggest convergence in inventive capabilities, and this finding gains some support when analyzing the intra-distributional dynamics of the invention capabilities. Paper IV specifically investigates whether the generation of renewable energy patents per capita has converged or diverged across 13 EU countries over the period 1990-2012. The results indicate the presence of conditional β- and σ-divergence in renewable energy invention abilities. This could be critical for assessing the future prospects of EU policy in the renewable energy field; divergence in terms of invention outcomes could imply a less rapid and yet more expensive goal fulfillment due to free-rider behavior and sub-optimal investment levels. Finally, Paper V tests for convergence/divergence based on countries’ public spending to renewable energy R&D. The empirical analysis focuses on the presence of conditional β-convergence across 13 EU countries over the period 1990-2012. The results suggest divergence in public R&D-based knowledge accumulation, and this is consistent with free-riding behavior on the part of some EU Member States. Energy import dependence and electricity deregulation also affect this divergence pattern. For instance, the higher the energy import dependence, the lower is the speed of divergence across the EU countries in terms of public R&D support. Overall, the diverging pathways in terms of both public R&D and private patenting efforts may raise concerns about an unfair burden-sharing in terms of renewable energy development efforts.