(Il)Legitimation of renewable energy projects – Legitimacy gaps in socio-technical transitions and actor responses

• We conceptualize (il)legitimation dynamics as actor responses to institutional complexity and legitimacy gaps. • We compare six onshore wind energy projects regarding the occurring legitimation and illegitimation dynamics. • We show how emerging legitimacy gaps open up transformative action spaces that enable project work and institutional work. • We find that (il)legitimation depends not only on regulative aspects but also on normative and cultural-cognitive dimensions. Legitimation is of central importance for the establishment of socio-technical configurations as sustainable alternatives in sustainability transitions. It is commonly conceptualized as alignment with institutionalized context structures. However, as transitions involve ongoing changes to these structures, institutions may become misaligned, highlighting ambiguities around both legitimacy and illegitimacy. These ambiguities often translate into conflicts over specific socio-technical configurations. We argue that, due to this institutional complexity, legitimation in transitions not only involves actors adapting configurations to existing institutions, but also actively and strategically shaping institutions themselves. Furthermore, we argue that these legitimation strategies are accompanied by processes of illegitimation, which equally contribute to institutional change through a dynamic interplay. To capture this interplay of (il)legitimation, we conceptualize legitimacy gaps as starting points where disagreements over (il)legitimacy in transitions become visible and are negotiated by heterogeneous actors. We propose a framework for analyzing how legitimacy gaps concerning concrete configurations emerge across different institutional dimensions (regulatory, normative, and cultural-cognitive), and how actors identify and respond to them. Empirically, we examine socio-technical configurations surrounding renewable technologies in energy transitions and present a comparative case study of six wind energy projects in Germany. By outlining the interplay between opposing (il)legitimation dynamics, the paper highlights how concrete projects function as active sites of institutional change in sustainability transitions. It shows how conflicts around renewable energy projects shape broader transition dynamics and offers an approach to analyzing contested implementation processes in changing institutional contexts.