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Subproject 5

Horizontal and high-temperature borehole storage (BTES)

Novelty of the solution of the subproject 

SP5 introduces a novel BTES approach by utilizing horizontal directional drilling (HDD) to establish a 3D-array of shallow horizontal boreholes. This method overcomes spatial restrictions in densely populated areas where vertical boreholes are unfeasible and it avoids legal and technical complications arising from the interaction of vertical systems with groundwater.

The core innovation in SP5's technology is the application of HDD to create horizontal boreholes of significant lengths, exceeding 1000 meters. SP5 aims to optimize heat transfer of BTES systems, thereby enhancing overall performance. The energy density of BTES is amplified through increased soil temperature (up to 50°C) and improved thermal stratification. Furthermore, SP5 seeks to integrate the horizontal BTES system with renewable energy sources, such as PVT systems and waste heat recovery. The goal is to formulate strategies that maximize synergistic benefits by exploiting the complementary nature of these technologies.

A unique aspect of SP5 is the development of simulation-based toolboxes for both planning and operation of BTES systems. These toolboxes, unlike conventional static calculation tools typically used in the field, provide a comprehensive understanding of the system's dynamics, facilitating precise predictions and informed decision-making.

Objectives of the subproject 


  • Advance the understanding of horizontal BTES and the effect of the borehole arrangement on the thermal stratification of soil-based TES.

  • Improve the understanding of the dynamic interaction of the individual boreholes in a  horizontal BTES system connected to a thermal grid.


  • Achieve specific investment costs for BTES below 200 CHF/m3 for systems beyond 10’000 m3 (m3 water equivalent). 

  • Enhance the economic profitability of integrated systems (particularly in combination with
    PVT/HP and waste heat recovery) by boosting the degree of self-sufficiency to 100% at grid

  • Decrease planning and operation expenditures by 20% through the use of the simulationbased toolboxes developed in SP5.


  • Enable seamless integration of 100% renewable energy sources into thermal grids through
    the optimized utilization of horizontal and high-temperature BTES.


  • Demonstrate the techno-economic feasibility of large-scale horizontal and high-temperature BTES systems exceeding 10'000 m3 (m3 water equivalent). 

  • Demonstrate the seamless interoperability between the long-term BTES system and  distributed short-term TES, ensuring efficient and reliable operation of the thermal grid.

Research partners

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