A new phase of energy transition makes auxiliary technologies such as energy storage and other flexibility options more important. Economic policy that aims to steer this transition needs to grasp the complex system dynamics underlying energy and society. This conceptual article gives an overview of energy technology innovation theories that exemplify the growing importance of flexibility for electricity usage. First, the article presents different conceptualizations of technology innovation and diffusion. Second, how energy systems are embedded in physical infrastructures and social power relations is shown with a brief history of electricity in contemporary industrialized societies. Third, energy innovation is discussed in context of challenges of the upcoming energy transition. Fourth, energy technology innovations are further contextualized in light of insights from political economy and energy social sciences. Finally, the discussed approaches are synthesized to amend the holistic technology innovation system approach for studying energy technology innovations such as energy storage.