Exploring the Potential of Aquifer Thermal Energy Storage in the European Energy Transition

“`markdown
Challenges and Opportunities for Aquifer Thermal Energy Storage (ATES) in EU Energy Transition Efforts—An Overview

Aquifer Thermal Energy Storage (ATES) systems present a promising solution for sustainable energy storage by utilizing underground aquifers to store and retrieve thermal energy for heating and cooling. As the global energy sector grapples with increasing energy demands, climate change, and the depletion of fossil fuels, transitioning to renewable energy sources becomes crucial. ATES systems play a vital role in these efforts by reducing greenhouse gas (GHG) emissions and enhancing energy efficiency.

This review employs the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) methodology to systematically collect and analyze relevant literature, emphasizing trends, gaps, and advancements in ATES systems. It focuses on simulation methods, environmental impacts, and economic feasibility, highlighting tools such as MODFLOW, FEFLOW, and COMSOL Multiphysics for optimizing design and system performance. Europe stands out as the continent most conducive for ATES implementation, thanks to its diverse and abundant aquifer systems, strong policy frameworks supporting renewable energy, and advancements in subsurface energy technologies.

1. Introduction

The global energy sector faces unprecedented challenges due to rising energy demands driven by population growth and industrial expansion. Simultaneously, the depletion of fossil fuel resources and the environmental impacts of their use heighten the urgency for a shift towards renewable and sustainable energy sources. To achieve a more sustainable and environmentally friendly future, it is essential to adopt energy solutions that fulfill current demands while aligning with global climate goals. One promising approach is the implementation of ATES systems.

ATES is a renewable energy technology that utilizes aquifers as natural underground reservoirs for storing and retrieving thermal energy, enabling efficient heating and cooling throughout the year. The system operates by leveraging the porous and permeable properties of aquifers, allowing water to be stored within the pore spaces of the subsurface material. Typically, it consists of two well systems: one for warm water storage and the other for cold water storage. During summer, excess heat is captured from buildings, industrial processes, or solar collectors and transferred to water, which is then injected into the warm well. Conversely, during winter, cooled water is injected into the cold well for storage. When thermal energy is needed, water is pumped from the respective well and circulated through heat exchangers to provide heating or cooling, completing the cyclical storage process.

Reducing reliance on conventional heating and cooling systems through ATES contributes to significant energy savings and reductions in greenhouse gas emissions. Research on ATES began in the 1970s, with Switzerland pioneering an experimental system in 1974 using a sand-and-gravel aquifer. The United States followed suit in 1976 with a three-phase experimental project at Auburn University aimed at assessing the feasibility of aquifer thermal storage. In the 1990s, China joined these efforts with numerical simulations and field experiments focusing on ATES applications in urban environments.

Currently, ATES systems are widely implemented in countries like the Netherlands, Sweden, and Denmark, where they are integrated into urban infrastructure to sustainably meet heating and cooling demands. The Netherlands leads globally in ATES adoption, operating over 80% of all systems worldwide and significantly reducing energy consumption and GHG emissions, particularly in cities like Amsterdam. Sweden and Denmark have also embraced ATES technology, with significant implementations in cities like Stockholm and at facilities such as Bispebjerg Hospital in Copenhagen.

While ATES systems have gained traction, their adoption faces challenges. Key market barriers include regulatory constraints, limited public awareness, and a lack of standardization. Environmental risks, such as hydrogeological, thermal, chemical, and microbiological impacts, have been highlighted in various studies. Despite these obstacles, the scalability and adaptability of ATES systems across diverse climatic and geological conditions indicate a promising future.

2. Methodology

The PRISMA method is a widely recognized framework designed to ensure transparency, rigor, and reproducibility in systematic reviews and meta-analyses. Initially developed in health sciences, PRISMA has gained traction in various disciplines, including renewable energy and environmental science. It enhances transparency in study selection and reporting, making it suitable for systematic reviews involving extensive data collection.

The literature search for this systematic review was conducted using four databases: the International Geothermal Association (IGA) Database, ScienceDirect, MDPI, and ResearchGate. The search began with a comprehensive keyword search for “Aquifer Thermal Energy Storage” or “ATES,” ensuring that the identified keywords were present in either the title or abstract of the publications. Subsequently, inclusion and exclusion criteria were applied to refine the initial pool of records, focusing on studies with full-text availability, published in English, and specifically centered on ATES. This filtering process reduced the initial 2500 records to 127 articles.

3. Results

A review of the extensive literature on ATES systems is essential for understanding the current research direction, identifying progress, and pinpointing areas requiring further development. The analysis of publication years indicates significant growth in ATES research activity, particularly between 2020 and 2025. The geographic distribution of the reviewed publications reveals that the Netherlands and Germany are the leading contributors, with substantial academic and industrial focus on advancing ATES technologies.

3.1. Temporal Trends in Research

Research activity on ATES systems has surged in recent years, with the majority of publications produced between 2020 and 2025, peaking in 2024. This trend underscores ATES as a critical area of interest in line with the global push for sustainable energy solutions.

3.2. Geographic Distribution of Research

The geographic distribution based on the affiliations of first authors highlights notable disparities in research activity. The Netherlands and Germany lead with the highest number of articles published, while other contributors include China, Belgium, the United Kingdom, Japan, and Switzerland.

3.3. Theme-Oriented Literature Review

The literature has been categorized into key themes, including prior review papers, studies exploring the potential of ATES, assessments of environmental impacts, and research on simulations of ATES systems.

3.3.1. Prior Review Papers

Numerous studies have summarized various aspects of ATES systems, focusing on environmental impacts, system performance, modeling approaches, and regional development.

3.3.2. Potential for ATES

The evaluation of ATES potential remains a barrier to its broader application, particularly in emerging markets. However, recent studies have begun to describe the potential of ATES systems at both global and regional levels.

3.3.3. Economic Properties

Economic feasibility is a key consideration for introducing ATES systems. Several studies have analyzed factors such as cost-effectiveness, return on investment, and operational efficiency.

3.3.4. Environmental Impacts

Reducing greenhouse gas emissions in the building sector is critical for addressing climate change. ATES systems offer a promising solution by efficiently storing and utilizing thermal energy in underground aquifers.

3.3.5. Simulation

Simulations are vital for understanding the operation and optimizing the design of ATES systems. Various methods have been employed to model the thermal and hydraulic processes within aquifers.

4. ATES Implementation in Europe

The widespread implementation of ATES systems across Europe reflects their potential to reduce greenhouse gas emissions, enhance energy efficiency, and contribute to the decarbonization of the heating and cooling sectors.

5. Discussion

While ATES is one of the most cost-effective underground thermal energy storage options, its applicability is highly dependent on aquifer availability and regulatory restrictions. The integration of ATES and other renewable energy sources remains underexplored, indicating a research gap.

6. Conclusions

The shift towards renewable energy has spotlighted sustainable storage solutions, with ATES systems emerging as a key approach. This review highlights advancements in simulation tools, economic considerations, environmental impacts, and practical implementations, particularly in Europe. While ATES systems significantly contribute to reducing greenhouse gas emissions and improving energy efficiency, challenges like regulatory barriers, public awareness, and environmental concerns still exist. Future research should focus on documenting successful ATES implementations, providing insights into their operation and benefits.
“`