In the energy transition, the promotion of renewable sources entails the development of storage technologies to manage the mismatch between energy production and demand. In this scenario, the use of CAES (Compressed Air Energy Storage) technology enables the efficient and cost-effective storage of large amounts of energy. However, this technology is developed in salt domes who have an inherent risk associated of underground exploration phase. To address this, we propose to develop an infrastructure (iCAES) in abandoned underground mines, where the exploration phase is completed and well known. For its implementation, this paper defines a structure hierarchization method gathers the technical and socio-economic criteria. It involves a multi-criteria problem, and the correct selection of the location must be based on specific mathematical algorithms. For this case the Analytic Hierarchy Process (AHP) from multi-criteria decision making (MCDM) methods allows quantified by means of a scientific and mathematical scale and the assignment of weights, so that it is possible to evaluate different alternatives. This is possible thanks to the application of the AHP model in absolute terms. The information gathering has been based on the specific case study of coal basins in the north of Spain, in the region of León. Considering the proposed methodology, the most suitable alternative locations to implement iCAES in the region of León were identified.

The increasing integration of renewable energy sources (RES) in Spain is leading to substantial amounts of surplus electricity, presenting a strategic opportunity for green hydrogen production as a key enabler of energy storage and decarbonisation. This study quantifies this untapped potential for 2024. Based on the difference between installed renewable capacity and actual generation, an economically viable surplus of 18,419 GWh was identified within an optimal 10-h operating window. The hydrogen production potential was modelled for three electrolysis technologies—Alkaline (AEL), Proton Exchange Membrane (PEM) and Anion Exchange Membrane (AEM)—using total energy consumption values of 57.40, 65.55 and 59.95 MWh/t H₂, respectively, including auxiliary systems. The estimated annual hydrogen production ranges from 280,999 t (PEM) to 320,897 t (AEL), with AEM yielding an intermediate value of 307,247 t. The analysis reveals a strong regional concentration, with more than 63% of the potential located in Castile and León, Andalusia, Castile-La Mancha and Extremadura. While this range represents an upper technical limit, it highlights the significant opportunity to valorise surplus renewable energy, contingent on targeted investment and a supportive regulatory framework.

Sustainability in the extractive and mining industry has become a key global concern, necessitating alignment with the United Nations Sustainable Development Goals (SDGs). This research introduces an innovative, scientific index-based assessment methodology designed to quantify the contribution of companies in these sectors to the SDGs. The methodology leverages a metric index scoring system to evaluate and enhance their sustainability performance.

In the context of sustainable development, revitalising the coal sector is a key challenge. This article examines how five innovative technologies can transform abandoned or in-use coal mines into sustainable energy centres. From solar thermal to compressed air energy storage, these solutions offer a path to a more sustainable future while addressing the decline in coal production. This approach not only promotes energy efficiency but also contributes to the mitigation of environmental impacts, thus consolidating the transition to a more responsible energy model. Thus, in this document, the reader can find the explanation of why we have opted for these technologies and not other existing ones. In addition, the economic, environmental and technical feasibility of the different technologies is analysed. Finally, real cases of the successful application of these technologies will be presented once they have gone beyond the project idea phase, and the reasons why we are calling for their transposition to the coal industry in the search for its revitalisation will be explained.

The integration of renewable energy with circular economy strategies offers effective pathways to reduce greenhouse gas emissions while enhancing local energy independence. This study analyses three real-world projects implemented in Spain that exemplify this synergy. LIFE Smart Agromobility converts pig manure into biomethane to power farm vehicles, using anaerobic digestion and microalgae-based upgrading systems. Smart Met Value refines biogas from a wastewater treatment plant in Guadalajara to produce high-purity biomethane for the municipal fleet, demonstrating the viability of energy recovery from sewage sludge. The UNDERGY project addresses green hydrogen storage by repurposing a depleted natural gas reservoir, showing geochemical and geomechanical feasibility for seasonal underground hydrogen storage. Each project utilises regionally available resources to produce clean fuels—biomethane or hydrogen—while mitigating methane and CO₂ emissions. Results show significant energy recovery potential: biomethane production can replace a substantial portion of fossil fuel use in rural and urban settings, while hydrogen storage provides a scalable solution for surplus renewable energy. These applied cases demonstrate not only the technical feasibility but also the socio-economic benefits of integrating waste valorisation and energy transition technologies. Together, they represent replicable models for sustainable development and energy resilience across Europe and beyond.

This study examines the association between the formal (de jure) adoption of renewable energy source (RES) support instruments and observed RES deployment outcomes across 36 European countries. We assess whether broader legislative adoption—measured by a transparent breadth/coverage index (SIC/OIL) based on binary coding and equal sector weights—correlates with higher RES shares. The empirical design comprises three complementary steps: (i) hierarchical clustering (Ward’s method; Euclidean distance on standardised indicators) to classify countries by legislative adoption profiles; (ii) parallel clustering of countries by RES utilisation profiles using 10 z-score-standardised outcome indicators (total and sectoral RES shares and per capita RES use by source); and (iii) an integrated comparison of both typologies, followed by a cross-sectional regression test of the OIL–RES association. Legislative and utilisation clusters do not systematically coincide, and the baseline regression shows a weak, statistically insignificant association with very low explanatory power (R² = ≈ 0.015), supporting heterogeneity (H1) rather than a universal positive average relationship (H₂). Interpretation is conservative because SIC/OIL captures policy-mix coverage (not budgets, enforcement, or design stringency) and because some low/zero policy entries may reflect limited source coverage. Overall, the findings suggest that observed RES performance is primarily shaped by country-specific structural conditions (resource endowments, economic capacity, and sustained long-term investment), implying that context-sensitive instruments and stronger implementation capacities should complement formal policy adoption.