One of the greatest challenges facing human civilization is the provision of secure, affordable energy without causing catastrophic climate change and environmental damage. Innovation in renewable energy technologies, which encompasses not only additional technology development but also widespread technology adoption, is widely considered by actors in the public and private sector alike to be one of the key areas where improvement is needed given the ability of renewable energy technologies to generate low-carbon and domestic energy. This panel is concerned with understanding the factors and policies that have contributed to cost reductions and an increase in technological options (diversification) in renewable energy technologies. The first paper by Laura Diaz Anadon and Christoph Wuestemeyer puts a new lens on understanding the drivers of energy innovation by focusing on the cross-sector technology spillovers. They examine the impacts of cross-sector spillovers on the cost of solar photovoltaic panels over time and identify the enablers of the spillovers. The second paper by Tian Tang focuses on assessing the impacts of R&D in wind turbine manufacturing, wind farm operating experience, and interaction between turbine manufacturers and project developers on wind farm productivity improvement in the US, measured by capacity factor. The third paper by Jung Eun Kim and Tian Tang evaluates the impact of different designs of renewable portfolio standards by U.S. states on the types of energy technologies ultimately adopted in the market. Technology diversification may be an important aspect of policies aimed at promoting innovation when there is uncertainty about the technology options that may be more appropriate and cost effective in the future. All three papers in this panel discuss what factors and policies drive innovation in renewable energy technologies, including R&D, spillovers, interaction between developers and users, and technology choices. By shedding light on the contribution of different mechanisms to promote innovation, this panel can help inform policy-makers about holistic and cost-effective ways to meet the energy challenge.