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Project description

“Underground Sun Conversion – Flexible Storage”: sustainable storage for the renewable energy system of the future

From December 2020, the “Underground Sun Conversion – Flexible Storage” (USC-FlexStore) project will investigate seasonal storage of large quantities of renewable energy to be made available year round.

This innovative international project is carried out with Swiss partners under the leadership of Energie 360°. It aims at developing a seasonal, high-volume transformation and storage solution for erratic renewable generation. Energy will be stored safely in gaseous form in underground facilities at depths of over 1,000 metres.

The aim of the project is to take RAG Austria AG’s patented “Underground Sun Conversion” (USC) technology (which involves methanation of CO2 and green H2) to the next level, and to design services based on it. Field tests are planned at RAG’s research facility in Pilsbach (Upper Austria).

In collaboration with Swiss energy supplier Energie 360° and research partners (WIVA P&G, BOKU Vienna, Empa, University of Bern, OST) working on this multi-disciplinary, transnational project, know-how and specific capabilities will be bundled. The research will focus on devising solutions to one of the biggest challenges facing the energy system of tomorrow: how to expand fluctuating generation of renewables such as wind and solar power while at the same time maintaining high levels of security of supply, especially in winter, when the possibility of generating power is low and demand is high?

Investigations will centre on the technological, commercial, energy-sector and legal requirements for a cross-sector approach that can reduce the current need for substantial imports and use of fossil energy in winter, when demand is stronger.

The goal is to enhance the interseasonal capacity of the USC-FlexStore storage system with a view to developing a commercial service. Compared with batteries or complementary storage services at pumped storage power plants, “USC-FlexStore’s” main advantages are its greater flexibility and much higher capacity. And this is what makes interseasonal energy storage possible in the first place.

In summer, ERA-NET recommended that the international “USC-FlexStore” research project receive funding. Subsequently, a transnational consortium agreement could be concluded between the partners as well as regional funding agreements with the respective state funding agencies - in Switzerland the Federal Office of Energy - BFE, and in Austria the Research Promotion Agency - FFG on behalf of the “Bundesministerium für Klimaschutz” (BMK) and the “Klima- und Energiefonds”. The project was launched in December 2020 and is scheduled to last for two and a half years.

Project information

This project is based on the “Underground Sun Conversion” (USC) technology developed by RAG Austria AG in collaboration with the University of Natural Resources and Applied Life Sciences, Vienna (BOKU), and represents the next step in implementing this new, innovative and unique storage technology.

“Underground Sun Conversion” involves injecting CO2 and H2 into a porous underground gas storage facility (a depleted gas reservoir), where microbial methanation has been found to occur, meaning the biological conversion of CO2 and H2 to methane, the main component of natural gas. This storage technology enables seasonal storage of large volumes of energy in the form of renewable gas. This will not only enhance the stability of European energy networks and energy supply, but is also essential for ensuring that the continent's energy mix includes a higher proportion of (gaseous) renewables.

The project will provide a first estimation of the potential for geological storage of energy in Switzerland using the "USC FlexStore" approach. This process serves as a blueprint for future expansion to other regions around the world, and in turn as a model for the internationalisation of the concept.

In line with European initiatives intended to promote sector coupling and the integration of electricity and gas grids, with a view to making the energy system more stable and flexible, the “USC-FlexStore” project is designed to contribute to achieving the overarching goals of the Strategic Energy Technology Plan and the ETIP SNET (European Technology and Innovation Platform – Smart Networks for the Energy Transition).


ERA-Net RegSys

This project is funded under the Joint Programming Initiative "ERA-Net Smart Energy Systems" under the priority "Integrated Regional Energy Systems" with support from the European Union's Horizon 2020 research and innovation program under grant agreement No. 775970. The Austrian participation in the ERA-Net Smart Energy Systems is funded by the “Bundesministerium für Klimaschutz” (BMK) and the "Klima und Energiefonds" while the Switzerland based contribution receives funds of the Swiss Federal Office of Energy.


Stephan Bauer

Head of Green Gas Technology

T +43 50 724-5377
M +43 664 811 9483

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