Compared with the storage technologies currently available for electricity, gas grids have enormous storage capacity. If electricity is converted into hydrogen, the existing infrastructure for natural gas, consisting of pipelines and gas storage facilities, can be used to buffer surplus energy from renewables.
Underground gas storage facilities have long since proved their worth in bulk energy storage. To date no investigations of how these facilities could store hydrogen – particularly where pore storage is involved – are available. In the flagship project on energy research “Underground SUN.STORAGE” an Austrian consortium headed by RAG (Rohöl-Aufsuchungs-Aktiengesellschaft) is for the first time investigating how to use underground gas storage space for long-term storage of energy from wind and sun by chemical means. The consortium includes Montanuniversität (University of Mining and Metallurgy) Leoben, the Interuniversity Department for Agrarbiotechnology (IFA-Tulln) within the University of Natural Resources and Life Sciences, Vienna (BOKU), the Energy Institute at the Johannes Kepler University (JKU) Linz, the electricity supplier Verbund and Axiom Angewandte Prozesstechnik GmbH.
The project is mainly concerned with how suitable underground gas storage facilities are for hydrogen. The aim is to demonstrate that hydrogen contents of up to 10 % are feasible. If this succeeds, the natural-gas storage facilities with their huge capacity (7 billion m3 in Austria, equivalent to 77,000 GWh) could play an important part in buffering energy from renewables in energy systems of the future. It must be shown that this type of storage is hydrogen-compatible even if the methanation route is chosen for the power-to-gas system, because a few percent of hydrogen residue remain in this case, too.
Power-to-Gas-Process, Source: RAG
In the power-to-gas process surplus electricity from PV and wind farms is used to dissociate water into oxygen and hydrogen by electrolysis. If desired, hydrogen obtained in this way can be then made to react with carbon dioxide to form methane or other hydrocarbons, liquid or gaseous. The only “waste product” from the process is oxygen (released when water is dissociated). The energy storage media hydrogen and methane can be used to generate heat and power, as fuel for vehicles or as raw materials for industrial processes.
The project involves a large number of laboratory experiments, simulations and model investigations, in order to predict how storage formations will behave when exposed to hydrogen or to typify microbial processes when hydrogen is fed into an underground gas storage facility. In addition, a full-scale field trial is being carried out in what was once a natural-gas field with characteristics similar to the major reservoirs tapped in Austria (Commune of Pilsach in Upper Austria). An assessment of risks, a life-cycle assessment and the analysis of the legal and economic setting are being carried out alongside the research work. The findings from the laboratory, simulations and the field test can be used to calibrate the simulation tools developed as part of the project – thus providing a basis for investigating many other types of storage structure all over the world.