Underground Sun Conversion - Start

Project description

Unique research project
Underground conversion and storage of wind and solar energy

For years, RAG has been dealing with the decarbonisation and transformation of energy systems. At the same time, with the increasing expansion of energy from renewable sources, the demand for large-volume and seasonal storage will increase, compensating for the seasonal fluctuations in energy harvest (summer sun) and energy demand (winter) and providing the usual level of security of supply. It is a service that cannot be provided by pump storage plants or batteries. Gas storage can provide the solution.

RAG Austria AG is Austria’s largest gas storage company – making it the country’s biggest energy storage provider – and one of Europe’s leading gas storage facility operators.

Project description

First, hydrogen is produced from solar or wind power and water, in an above-ground facility, and then injected with carbon dioxide into an existing (porous) natural gas reservoir. At a depth of over 1,000 metres, in a relatively short time naturally occurring microorganisms convert these substances into renewable gas which can be stored in the same reservoir, withdrawn as needed at any time, and transported to consumers via the existing pipeline network.

The aim of the research project is to use existing gas (pore) reservoirs as natural bio-reactors. The methanation process and storage take place naturally in underground pore reservoirs. This represents a huge source by potentially providing the urgently needed flexibility which renewable energy sources currently lack. Initial laboratory tests conducted as part of the forerunner project, Underground Sun Storage – which is also supported by the Austrian Climate and Energy Fund – show that hydrogen and carbon dioxide injected into the reservoir are converted into methane by microbiological processes. This enables the creation of a sustainable carbon cycle.

Laboratory tests, simulations and a scientific field test at an existing RAG reservoir will be carried out in collaboration with a group of project partners. A further objective is to test whether the outcomes can also be achieved at many other reservoirs all over the world. The striven results are therefore of outstanding importance for a successful energy transition.

RAG Austria AG has therefore been making considerable efforts in research and development for years to evolve storage solutions for structuring the supply of renewable energy as required. We see ourselves as a partner of renewable energies. An already widely discussed solution for the storage problem is the „power-to-gas“ technology. The surplus electricity from solar and wind energy splits water into oxygen and hydrogen. Electricity (electrons) is then converted into hydrogen (storable molecules). Thus hydrogen becomes an energy carrier. In our unique „Underground Sun Storage“ flagship project, we have been working with partners to test the storage of hydrogen in depleted natural gas reservoirs as part of an in-situ field trial. In the framework of this project, we were able to gain many positive insights that motivated us to continue. A key finding led to the current project „Underground Sun Conversion“, which will be presented in more detail in this brochure. Hydrogen and carbon dioxide can be converted into methane = renewable natural gas in suitable natural gas reservoirs through a microbiological process. This energy conversion as well as the increase in energy density and energy storage take place invisibly in the porous rock at depths of more than 1,000 metres. Under the leadership of RAG Austria AG, the Underground Sun Conversion project is being carried out by an Austrian consortium and supported as part of the energy research program of the Austrian Climate and Energy Fund as a flagship project. The research project should be completed by 2021.

“The energy carrier gas can be transported in large quantities safely and invisibly in existing underground infrastructure and environmentally friendly stored in natural gas reservoirs. Due to its good geological preconditions for storage, Austria can make a significant contribution to Europe‘s security of supply.“

Geological history in fast motion: Producing natural and renewable gas

This unique method recreates the process by which natural gas originates, but shortens it by millions of years – like geological history in fast motion. The time advantage is primarily due to two factors. On the one hand, organic substance must first be built up in natural formation (in principle, solar energy should also be stored). These organic substances die off, are decomposed and converted to (methane) natural gas. This process is shortened in Underground Sun Conversion technology by going straight into the process with the starting materials of the last conversion step.

Secondly, the use of fossil natural gas requires a sedimentation process that produces porous storage structures with a corresponding clayey covering layer. This process takes a long time and only then can gas be stored in the geological structures. At that time, much methane was immediately returned to the carbon cycle, as is still the case in wetlands today. By using already existing suitable reservoirs, no sedimentation process has to be awaited, and the risk of developing suitable stratigraphy is eliminated. In total, geological time periods can be skipped by using existing geological structures - hence „Geological history in fast motion“.

This environmentally friendly process has three major advantages:

  • Carbon neutral
    Renewable natural gas is carbon neutral if CO2 that is already present – for example, from burning biomass – is utilised and absorbed 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 problem of storing 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.


Stephan Bauer

Head of Green Gas Technology

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

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