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Project description

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Underground Sun Storage – storing energy from wind and solar power below ground

Harvesting, storing and supplying solar energy: an unprecedented pilot project run by RAG is currently testing this groundbreaking approach to energy production and storage.

Storage of hydrogen produced using solar energy is being trialled at a small depleted gas reservoir in Pilsbach, Upper Austria. Energy from renewable sources that can be retained thanks to storage offers the only straight replacement for conventional energy – and Austria’s gas storage facilities provide the necessary infrastructure. The project is being financed by Austria’s Climate and Energy Fund.

Project outline

In most cases, energy from renewable sources lacks flexibility. Neither wind nor solar power can be con­trolled to meet actual energy demand. But the electricity grid cannot store energy, so grid operators have to adjust generation precisely to demand. If it were possible to store large amounts of power and inject it back into the grid when needed, generation would no longer be tied to demand. That is why huge energy storage facilities are essential in a world that relies on renewables. In nature, carbon and hydrogen have evolved as primary sources of energy, and the main substances in which energy is stored. We have taken this process as a model and imitated it with power to gas technology. Using electrolysis, excess energy generated from renewables is transformed into hydrogen, which can be stored in the natural gas network. A range of tests are being conducted to investigate how the natural gas infrastructure tolerates hydrogen. These have already shown that the existing infrastructure seems to cope well with hydrogen content of up to 10%. 

Whether underground gas storage reservoirs can tolerate hydrogen is still unclear, and that is the main focus of this groundbreaking project. If the results are positive, the role of such facilities and their enormous storage capacity (more than 8 billion cu m in Austria, equivalent to 92,000 GWh) in the energy system of the future will change significantly, since they can be used to store and balance out supplies of renewable energy. Within this lead project, we are attempting to demon­strate the ability of underground storage facilities to tolerate hydrogen content of up to 10% in gas, so that they do not have to limit the potential of the network as a whole.

To achieve this aim, the project comprises laboratory experiments, simulations and a field trial conducted on an industrial scale at an existing storage reservoir with similar characteristics to Austria’s large storage facilities. The tests are being accompanied by a risk assessment, a life cycle assessment, and an analysis of the legal and economic framework conditions. Simulation tools developed in the project will be calibrated by collating the results from the laboratory tests, simula­tions and the field trial. The goal is to enable similar investigations for many other storage facilities, all over the world.

Finding a solution to the question of storing renewable energy is the key to maximising its contribution to the energy mix and achieving a substantial reduction in carbon dioxide emissions. In terms of the strategic development of energy systems for the future, the results of the pilot will be hugely significant for companies, political decision-makers and public authorities.

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