AbstractStudy regionThis study is conducted across groundwater bodies within mainland Spain, as defined under the European Water Framework Directive.Study focusWe conduct a preliminary, national-scale assessment of groundwater-body suitability for Aquifer Thermal Energy Storage (ATES) in Spain from a water-energy nexus perspective. The methodology is based on two complementary indicators derived from long-term piezometric records: (i) a Drought Stress Response Index (DSRI), reflecting aquifer reliability, resilience, and vulnerability over decadal time scales, and (ii) groundwater-level variability and long-term trends as proxies for hydraulic stability. Together, these indicators support a first-order screening of groundwater bodies from less suitable to more suitable conditions for ATES operation.New hydrological insight of the regionThe analysis of drought-response indicators reveals clear spatial patterns in aquifer vulnerability, resilience, and reliability across Spain, with only weak correlations with mean groundwater levels. Groundwater-level amplitude and trend analyses indicate that unstable conditions are concentrated in southern and eastern Spain, whereas northern regions generally exhibit more stable regimes. Building on these indicators, the results reveal pronounced spatial contrasts in ATES suitability, with generally more favorable conditions in northern regions and lower suitability in large parts of southeastern Spain, while extensive areas with intermediate suitability are also identified. Based on this national-scale screening, the study provides a preliminary assessment of ATES suitability for the main Spanish urban areas, offering an initial indication of where groundwater conditions are more or less favorable for ATES deployment.

Recent studies confirm the potential efficiency of geothermal resources for maintaining comfortable building temperatures through cooling and heating solutions. In addition, a variety of initiatives have been promoted to effectively reduce both environmental concerns and energy crisis by the integration of renewables. Under this framework, this paper describes and assesses hybrid geothermal and photovoltaic (PV) installations to provide sustainable solutions. Hybrid geothermal–PV systems are evaluated as a strategic opportunity to increase the presence of geothermal energy within the hybrid heating, ventilation, and air-conditioning (HVAC) market. While upfront capital costs associated with geothermal technology can suppose some barriers, the synergistic coupling with PV installations can provide a compelling solution and reliable energy supply, in terms of both economic feasibility and the energy (electricity) consumption. With this aim, a detailed economic and energy analysis is then conducted to evaluate such hybrid solutions connected to the grid, including potential energy storage system. HVAC demand optimized battery energy storage system (ESS) and PV installation connected to the grid are considered as hybrid renewable solution in a Mediterranean location case study based on the tertiary and industry sectors. It is carried out by the authors from real energy demand data collected for 3 years. Simulation results demonstrate that the proposed hybrid system reduces electricity consumption by 25% compared to a conventional air-to-air HVAC configuration, while geothermal operation achieves 34% lower heating demand and 26% lower cooling demand. These improvements highlight the hybrid system potential for enhanced energy efficiency and load-shifting capability in tertiary and industry sectors.

Water scarcity is an increasingly critical global issue, driven by population growth, industrial development, and the effects of climate change. Desalination has become a weighty strategy to ensure freshwater supply, particularly in arid and water-stressed regions. However, deploying desalination plants presents challenges such as high energy demands, environmental impact, and the need for sustainable site selection. This study proposes an integrated spatial analysis method that combines geographic data with multi-criteria decision-making to identify suitable locations for desalination facilities. The approach evaluates factors such as land availability, climatic conditions, energy costs, environmental risks, brine discharge, and eutrophication potential. A decision-analysis technique was used to balance competing objectives and produce suitability maps. The proposed method also incorporates strategies to minimize environmental impacts, including technologies that eliminate liquid waste and use renewable energy sources. A case study was conducted across the European continent. The analysis identified 3,309 suitable sites for desalination plants, located in both coastal and inland areas, covering approximately 10% of the continent's land surface. These results demonstrate the feasibility of implementing advanced desalination systems beyond traditional coastal zones. The resulting framework offers a scalable and adaptable model for sustainable water resource management in diverse environmental and geographic contexts.

The growth of the urban population intensifies climate change due to the increase in activities that emit greenhouse gases, such as heating. However, proper urban planning and effective environmental policies can mitigate these impacts and foster a sustainable future. This study proposes an optimized spatial tool to implement renewable coupled heating systems in urban areas, combining geothermal heat pump technology with electricity generation through photovoltaic panels. The tool performs an exhaustive geospatial analysis that considers technical, economic, and socio-environmental criteria, offering multiple alternatives prioritized through multi-criteria evaluation methods. This facilitates the design of various scenarios according to the investment in renewable coupled systems for heating in buildings, in line with Sustainable Development Goals (SDG) 7, 11, and 13. The tool is evaluated in the city of Madrid, specifically in the neighborhood of Ciudad Lineal, generating a total of 2733 alternatives. Four scenarios are designed based on the annual subsidies provided by the Spanish Institute for Energy Diversification and Saving (IDAE) for heating and cooling using renewable energy sources. The first scenario, which includes 599 alternatives, manages to avoid emissions of 5 MtCO₂/year and primary energy savings of 278.9 GWh/year.