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Underground Sun Conversion – Flexible Storage

USC Technology: Geological history on fast forward

Over 1,000 metres below ground, where natural gas formed millions of years ago, a unique, highly innovative method is recreating the process by which it originated.

Hydrogen and carbon dioxide are injected into suitable depleted natural gas reservoirs, where they are converted into methane (green gas) by a microbiological process. Converting the energy, densifying it and storing it all take place out of sight, in porous rock formations at depths of over 1,000 metres. 

Natural production of green gas

RAG holds an international patent for this process, which is called hydrogenotrophic methanogenesis. Both methanation and storage take place naturally. The project’s huge potential lies in the fact that it can provide the urgently needed flexibility which renewable energy currently lacks, heralding the creation of a sustainable carbon cycle.

The multidisciplinary, international follow-up project entitled Underground Sun Conversion – Flexible Storage (USC-FlexStore), is further developing the technology tested in the Underground Sun Conversion project and designing green gas storage and production services based on the research findings. Field tests were carried out at RAG’s hydrogen facility in Pilsbach, Upper Austria. This flagship project is being financed by Austria’s Climate and Energy Fund as part of its energy research programme.

Benefits at a glance 

  • Carbon neutral: Green Gas is carbon neutral when carbon dioxide that is already present, e.g. as a result of biomass combustion, is captured by the production process. This creates a sustainable carbon cycle.
  • Renewable energy becomes storable: Solar and wind power output fluctuates due to changing weather conditions, meaning that production cannot be adjusted to demand. The quandary of how to store renewable energy is solved by converting it into renewable natural gas.
  • Use of existing infrastructure: Infrastructure already in place can be used for the natural production process, as well as for underground storage in natural gas reservoirs, and environmentally friendly transportation to consumers.

“Archaea are the stars of the energy transition. We feed these microorganisms in our pore reservoirs with hydrogen and carbon dioxide – and they make them into natural, climateneutral green gas.”


Stephan Bauer

Head of Green Gas Technology

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