Cross-technology legitimacy feedback: The politics of policy-led innovation for complementarity in concentrating solar power

•Technological learning is insufficient for accelerating deployment of maturing technologies.•Dynamic diffusion of adjacent technologies can negatively affect technological legitimacy and policy support.•Increasing complementarity with dynamic technologies can increase technological legitimacy.•Cross-technology legitimacy feedback turned concentrating solar power into a storage rather than a generation technology. Solar photovoltaic and wind power generation is expanding fast globally, fuelled by technological progress and rapid cost reductions. Other renewable power technologies fare much worse: deployment stagnates despite substantial technological progress. Here, we explore why these technologies fall off political agendas although they are improving, proposing that negative cross-technology feedback from more dynamic, faster deployed technologies reduce the legitimacy of laggard technologies. This generates political pressure to cancel or adapt support schemes, which in turn may push the laggard technology to change and become more complementary to the dynamic technologies. We illustrate our propositions with a case study of concentrating solar power (CSP) policy and deployment in three countries. We show how negative legitimacy feedback from the dynamic diffusion of photovoltaics and wind power in the 2010s led to both policy termination and technological adaptation towards complementarity, changing CSP from a generation to a storage and balancing technology.