Underground Sun Storage

By RAG Austria AG (Austria)

Harvesting, storing and supplying solar energy: an unprecedented pilot project run by RAG Austria AG has tested this groundbreaking approach to energy production and storage.

It demonstrated the storability of wind and solar energy in existing natural gas reservoirs on large scale by transforming it into hydrogen using electrolysis.

Technical aspects

• In 2013, RAG Austria AG started to investigate the tolerance of hydrogen in underground gas storage facilities in a depleted underground natural gas reservoir.
• The goal of the project was to demonstrate that specific gas storage reservoirs can tolerate hydrogen content of up to 10 %. This goal was successfully achieved.
• This means that naturally formed gas storage reservoirs with similar characteristics are not a limiting factor within the gas system as a whole, and with their vast storage capacity, their role in the energy system of the future could change significantly, since they can be used to store and balance supplies of renewable energy.
• The project comprised laboratory experiments, simulations and a field trial conducted on an industrial scale at an existing reservoir with similar characteristics to Austria’s large developed storage facilities.
• The tests were accompanied by a risk assessment, a life cycle assessment, and an analysis of the legal and economic environment. Simulation tools developed in the course of the project were calibrated by comparing the results of the laboratory tests, simulations and the field trial. They will make it possible to investigate many other structures around the world in the same way.

Contribution to energy transition

With this project it was possible for the first time to gain actual interdisciplinary insight into the storage of hydrogen in a subsurface gas storage with the inclusion of an actual field test.

This project allows the storage of solar energy during the summer to be injected back into the grid during winter when demand increases. Therefore, it offers a solution to the challenge of storing intermittent renewable energy.

The role of such facilities and their enormous storage capacity in the energy system of the future has changed significantly, since they can be used to store and balance out seasonal supplies of renewable energy. The results enable similar investigations for many other storage facilities, all over the world.

Outlook

In the next step, a project for storing 100% hydrogen is in preparation.