Borehole thermal energy storage systems: A comprehensive review using bibliometric and qualitative tools

Borehole thermal energy storage systems are emerging as a promising technology for storing intermittent renewable thermal energy sources. BTES systems utilize the underground as a thermal reservoir, where heat is stored during periods of excess energy production and retrieved when needed. This enables these systems to address the challenge of matching the supply of renewable energy with the demand for heating and cooling in buildings. This approach not only enhances the efficiency of renewable energy systems but also contributes to reducing greenhouse gas emissions and reliance on fossil fuels. This study introduces a novel approach to literature analysis in the BTES field by employing bibliometric and qualitative analysis tools, including SciMAT, VOSviewer, and NVivo, providing a systematic alternative to traditional manual review methods. The goal is to identify key publications, summarize their findings, and track the evolution of research directions over time, enhancing the understanding of the field. The paper is structured into six sections. The first section provides an overview of analytical and numerical models used to simulate the performance of BTES systems. The second section discusses the differences between traditional literature review methods and those employing bibliometric and qualitative analysis tools, highlighting their respective limitations and benefits. Additionally, it compares studies that have analyzed the BTES field using traditional review methods, explaining why a literature review with bibliometric and qualitative analysis tools is necessary and what advantages they offer. The third section outlines the research structure and employs bibliometric metrics to identify significant publications in the BTES field, while the fourth section uses SciMAT, VOSViewer, and NVivo to create scientific maps and networks of keywords, documents, publication sources, and active countries, revealing major research themes and influential publications. The fifth section organizes BTES publications into seven groups, reviewing selected studies within each to highlight recent developments, while the final section evaluates the dispersion of these studies to pinpoint well-researched areas as well as areas that require further exploration within the BTES field. The study highlights a growing interest in BTES research and identifies gaps in areas such as regulatory frameworks, market status, environmental impacts, and integration with smart energy systems. It also emphasizes the need to further investigate the thermal effects of groundwater, grout, ground thermal properties, and ground temperature imbalances on BTES system performance, underscoring the importance of continued research to address challenges and advance the development of BTES systems.