This Article analyses the evolution of the public security defence to justify restrictions on free movement within the EU in the context of the energy sector. Taking the seminal 1984 Campus Oil case as the point of departure for its analysis, the Article focuses on the interplay between public security and energy security and shows two key changes in the case law of the Court of Justice of the European Union. First, it demonstrates how the scope of the public security defence in the energy sector has gradually narrowed. Second, it shows how the public security defence has developed to take into account evolving social, technological, and legal contexts in the EU energy sector. Culminating in cases like Hidroelectrica in 2020 and OPAL in 2021, analysis of the relevant case law suggests that, despite the societal dependence on energy and the ongoing geopolitical turmoil in Europe, the Court of Justice interprets exceptions from free movement in an increasingly strict manner, highlighting the primacy of internal market approaches to energy security.

This article explores the meaning of solidarity in European Union (EU) law in the context of the energy sector and the ongoing energy crisis. Energy provides a powerful and topical sectoral example of the fundamental role and diverse functions of solidarity in EU law. In its OPAL ruling in 2021, the Court of Justice of the EU established that energy solidarity constitutes a legally binding principle of EU energy law that should inform EU institutions and the Member States in their energy decisions. This article adds to legal scholarship on solidarity in three ways. First, it further develops the understanding of the ambiguous solidarity concept in EU law through the lens of the energy sector. Secondly, it contributes to the emerging body of energy law scholarship that seeks to advance the discipline of energy law by focusing on its doctrine rather than on its substantive developments. Finally, it provides a timely and novel analysis of the EU's recent emergency responses to address the acute energy crisis from the point of view of solidarity.