VHT-STORAGE (Very High-Temperature Borehole Thermal Energy Storage) is developing and demonstrating a new approach to seasonal thermal energy storage, combining concentrated solar thermal energy with very high-temperature borehole thermal energy storage (VHT-BTES). The project aims to store solar heat underground at temperatures of 110-140°C, transferring renewable heat generated during periods of high solar production to the winter heating season.
A field laboratory in Uppsala, Sweden, will combine high-temperature boreholes with solar collectors from Absolicon. Alongside the physical demonstration, the project will develop a digital twin for modelling, monitoring and optimizing the integrated energy system.
The project brings together MG Sustainable Engineering AB, Absolicon Solar Collector AB, Crown Tech ApS, Uppsala University and the Technical University of Denmark (DTU), combining expertise in solar thermal technology, underground energy storage, geoscience, energy-system modelling and digitalization.
Project overview
| Project period | April 2026 – March 2029 |
|---|---|
| Project status | Ongoing |
| Funding | This is a Eurostars project with funding from Vinnova for the Swedish participation. |
| Project coordinator | MG Sustainable Engineering |
| Absolicon’s role | Solar thermal technology provider and lead of system design and component specification. Absolicon contributes to the solar collector field, system integration, installation and commercialization activities. |
Background and challenge
Solar thermal energy production and heat demand do not always occur at the same time. In northern European climates, solar production is highest during the warmer part of the year, while demand for heating peaks during winter. Seasonal thermal energy storage provides a way to bridge this gap by storing heat over several months.
Conventional borehole thermal energy storage systems typically operate at considerably lower temperatures. VHT-STORAGE aims to advance the technology by storing heat at 110-140°C, allowing high-grade solar heat to be stored underground and later supplied to heating systems.
Operating borehole storage at these temperatures introduces new technical challenges relating to thermal losses, materials, geological conditions, long-term subsurface behavior and the integration of the different system components.
The project therefore combines physical demonstration with advanced modelling and monitoring. A digital twin will be developed to simulate the complete system, helping optimize its design and operation and reducing technical risks when the concept is scaled to new locations.
The project also investigates the potential for in-situ thermal soil remediation, where the elevated underground temperatures could be used to treat contaminated soil while the site simultaneously functions as an energy-storage asset.
Absolicon’s contribution
Absolicon provides the solar thermal technology required to charge the underground storage with high-temperature renewable heat.
Absolicon leads Work Package 2, System Design & Component Specification, which translates the VHT-STORAGE concept into a detailed engineering design. The work includes system requirements, integrated design of the solar field and storage system, component selection and interface coordination between the project partners.
Absolicon’s contribution includes:
- Defining system requirements and operational parameters together with the consortium.
- Leading the detailed engineering design of the integrated solar field, borehole storage, heat exchangers and control system.
- Selecting and procuring relevant components.
- Coordinating design reviews and interfaces between the different subsystems.
- Installing and integrating the solar collector field and associated pipework.
- Supporting commissioning and testing of the complete demonstrator.
- Contributing to the commercialization and future scale-up of the technology.
The project gives Absolicon the opportunity to validate concentrated solar thermal technology in a new application: very high-temperature seasonal underground storage, where solar heat generated during summer can be made available for district heating during winter.
Expected results and impact
The main expected result is a validated VHT-STORAGE system combining concentrated solar thermal energy, very high-temperature borehole storage and intelligent energy management. During the project, the technology is planned to advance from TRL 4 to TRL 6.
A key result will also be a digital twin platform using physical models and data from the demonstration installation to simulate system behavior, optimize operation and support the design of future installations.
The project is expected to contribute to:
- Very high-temperature seasonal heat storage at 110–140°C.
- Storage of solar heat from summer to winter, increasing the potential contribution of solar thermal energy to year-round heat supply.
- Reduced emissions and auxiliary energy use through increased use of directly stored renewable heat.
- A validated digital twin for monitoring, optimization and future system design.
- Improved site assessment and modelling methods for high-temperature underground storage.
- Development of thermal soil-remediation methods as an additional application of the technology.
- Improved scalability and investment confidence through real-world demonstration and measured performance data.
- Further commercial development of seasonal solar thermal storage for district heating and other large-scale heat applications.
The technology developed within VHT-STORAGE will also form a foundation for further research. The subsequent Sun For the Winter (SFW) project builds on the VHT-STORAGE field laboratory and will add intelligent control using a calibrated digital twin and AI-based Energy Management System to further optimize charging and discharging of the borehole storage.
Funding
VHT-STORAGE is an Eurostars project coordinated by MG Sustainable Engineering AB with funding from Vinnova for the Swedish participation.
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