In many places, the electricity sector is transitioning towards greater share of renewable energy technologies. In the initial phase of the transition, a primary concern for research and policy was to establish renewables as technically and economically viable options. Today, the situation is different: renewables are diffusing rapidly in many electricity grids, thereby generating major changes for existing technologies, organizations and infrastructures. In this new phase of the energy transition, we do not just witness an acceleration of earlier transition dynamics, but also qualitatively new phenomena. These include a complex interaction of multiple technologies, the decline of established business models and technologies, intensified economic and political struggles of key actors such as utility companies and industry associations, and major challenges for the overall functioning and performance of the electricity sector (for example, when integrating renewables). Drawing on a transition studies perspective, this paper compares the two phases and discusses implications for research and policymaking.