From Grey to Green: A Three-Decade Longitudinal Study of Environmental Assessment as a Metric of National Energy Transitions

This research examines the structural evolution of environmental assessment in Spain over a 35-year period (1991–2025), serving as a longitudinal case study for the transition of mid-sized developed economies from industrial-age infrastructure to a decarbonized energy model. The study introduces a novel approach by utilizing Environmental Assessment records to evaluate national strategic directions and quantify developmental intent via administrative proxies. The analysis utilizes a comparative quantitative study of Strategic Environmental Assessments and Environmental Impact Assessments of national and supranational projects. Administrative trends were contextualized within major socio-economic and geopolitical events, including global financial crises, public health emergencies, and energy security developments, to identify potential external influences. The data reveals a paradigm shift. While the period 1991–2010 was dominated by grey infrastructure (transport and civil engineering), the post-2018 era shows an unprecedented increase in renewable energy dossiers. Between 2021 and 2025, energy projects dominated the regulatory workload, accounting for 73.86% of total processed dossiers, and reaching a single-year peak of 84.56% in 2022. National and international legal, economic, and social events, such as European Green Deal mandates and the NextGenerationEU recovery funds, have an apparent alignment with a country’s development strategy. We highlight the challenges and risks of such an exponential change in the energy model. For mid-sized developed economies, these findings suggest that Environmental Assessment data is an essential tool for navigating the complexities of rapid decarbonization and identifying systemic gaps in strategic planning.