Underground Sun Conversion - Start

Experimental facility

Schematic representation of experimental facility

01. Electrolysis

This is where hydrogen is generated from electric current. After cleaning the well water through a reverse osmosis system, the water is decomposed into hydrogen and oxygen by direct current. The hydrogen is dried and mixed with CO2 and natural gas forwarded to the compressor. The oxygen is released as a by-product to the atmosphere.

02. CO2 - Tank

For microbiological methanation in the reservoir, CO2 is added to the process. CO2 is supplied in liquid form and stored in a buffer tank on site and can be added as needed. The CO2 comes from a biogenic source.

03. Compressor station

To bring the gas mixture methane / hydrogen / CO2 to the required pressure in order to to be able to bring it into the reservoir, a compressor is needed. Here is a so-called piston compressor machine used. A maximum accumulator pressure of 60 bar is planned.


04. Injection well

The injection and withdrawal in batch operation take place via a well, which is equipped with appropriate safety features. In later cycle operation, this well is only used for storage.

05. Gas reservoir

Millions of years ago, natural gas reservoirs were created in the pores of the sandstone, which are sealed by more than 100 m thick clay layers. Here, large quantities of energy can be stored sustainably, safely and invisibly.
In the Underground Sun Conversion project, the microbiological generation of renewable natural gas will be restarted, a process that took place exactly here millions of years ago.

06. Withdrawal well

The removal of renewable natural gas takes place from the cycle operation via its own well, which is also equipped with appropriate safety features.

07. Drying unit

In a subsurface reservoir gas is absorbing moisture. Therefore, before the gas is discharged into the downstream systems and the pipeline network, a drying is required.

08. Gas conditioning

The gas taken from the reservoir may still contain residual unreacted hydrogen and carbon dioxide. In the course of the project, a membrane separation process is therefore being tested in order to reduce these gas components to a specification-compliant level.

09. Electricity grid connection

The Underground Sun Conversion Project is about storing renewable electricity by converting it into a storable energy source. The renewable electricity is supplied via the power grid and transformed via a transformer to the required voltage levels.

10. Control unit / EMSR

At this point all information comes together, measurement data is processed and forwarded for evaluation. The system operates autonomously during normal operation and is monitored by the headquarters in Gampern. In the event of any fault messages, the on-call service reacts.




Max. pressure

107 bar




 1,027 m

Working gas volume        

1.7 mn cu m

Reservoir volume              

6.2 mn cu m



Installed power                        

500 kW

100 cu m H2/h


Stephan Bauer

Head of Green Gas Technology

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

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