Gas storage for a secure energy supply

The natural gas storage facility in Jemgum.

Current situation and review

The next winter is just around the corner and the new heating period has already begun. After the experiences of last winter, the question arises once again as to how stable the German gas supply is at the moment and whether our gas storage reserves are really sufficient to get us through the cold season.

The starting position for the coming winter is much better than last year, when we found ourselves in a difficult supply situation after Russia cut off its gas supplies. The Federal Network Agency now considers the risk of a tight gas supply in a normal cold winter to be low, as not only have the feed-in options from LNG plants been expanded, but the lack of Russian supplies has also been compensated for by gas from Norway, the Netherlands and Belgium.

The fact that gas storage levels are currently above 99% is also significant. A regulation introduced last year under the new Gas Storage Act requires storage facilities to be 95 % full by November 1. According to the German government, this amount corresponds to the consumption of two to three average cold winter months. This requirement has therefore already been met on time!

Nevertheless, the all-clear cannot be given for a gas shortage, as a very cold winter would cause gas consumption to rise sharply. In addition, Germany would also have to supply some neighboring countries in the event of a gas shortage. Further damage to pipelines in the North and Baltic Seas cannot be completely ruled out either.

In order to take account of the remaining risks, the Federal Network Agency recommends using gas sparingly in the coming period.

The current storage levels can be called up at any time in the Federal Network Agency's situation report. There are also various forecasting models that calculate new storage scenarios for the coming winter using the observed values from recent years, in particular from 2022. With individual parameter settings such as "import inflows", "weather conditions" and "changes in consumption", certain developments can be simulated and the potential risks for the upcoming gas supply can be forecast in adjusted future scenarios. Such a model can be found, for example, on the DVGW website.the possible risks for the upcoming gas supply can be forecast in adjusted future scenarios. Such a model can be found, for example, on the DVGW website.

Tasks and capacities of gas storage facilities

As the filling levels of gas storage facilities have recently become more important and are no longer taken for granted, an overview of the basic tasks and functions of gas storage facilities is provided here.

Germany has few gas reserves of its own and has to secure its supply primarily through imports. German gas storage facilities play an important role in ensuring security of supply and price stability. They balance out fluctuations in daily and seasonal gas consumption and act as a buffer system to ensure reliable security. In winter, up to 60 % of consumption in Germany is covered by German gas storage facilities.

An overview of the current daily capacities, including the geographical location of German gas storage facilities, can be found on the INES storage map. Current filling level data on gas storage in Europe is provided by the European Gas Storage Association GIE on the AGSI+ website.

Across Germany, there are a total of around 40 storage sites with 47 gas storage facilities, including 31 cavern and 16 pore storage facilities with a total volume of around 23.3 billion m3 of working gas. This corresponds to just over a quarter of German gas consumption, which amounted to 847,470 GWh in 2022 according to the Federal Network Agency.

Gas traders or gas suppliers can rent space in gas storage facilities from the operating companies to temporarily store purchased gas. This gas is transported to the gas storage facility via long-distance pipelines.

Location and advantages of gas storage types

An underground storage facility stores gas in natural or artificial cavities beneath the earth's surface at depths of a few hundred to two thousand meters.

Storage options in the geological underground.

Schematic comparison of cavern and pore storage facilities.

There are two types of underground natural gas storage facilities in Germany: pore storage facilities and cavern storage facilities. The two types of storage not only differ geologically, but also have different advantages.

While suitable salt formations for caverns are mostly located in northern Germany, the geological conditions for creating pore storage facilities are available in almost all regions of Germany.

However, economic aspects can also influence the location of the storage facilities. For example, the locations are usually close to consumption centers or at important interconnection and border crossing points of the German transmission system.

Cavern storage facilities are cavities that are given a cylindrical shape by the targeted brining of salt domes. The caverns can reach heights of 500 m and volumes of up to 800,000 m3.

Up to 1 million m³ of gas can be withdrawn from the Jemgum cavern storage facility in a single hour.

The cavities in the salt make it possible to inject or withdraw the entire storage volume within a very short time, as they are directly connected to the above-ground storage reservoirs via a deep borehole. Example: Up to 1 million m³ of gas can be withdrawn from the Jemgum cavern storage facility in a single hour. Cavern storage facilities are therefore particularly suitable for balancing short-term, high fluctuations in demand.

Pore storage facilities are located in natural water-bearing aquifers or former gas and oil reservoirs whose underground storage rock usually consists of limestone or sandstone. The reservoirs are provided with gas-impermeable cover formations. The storage volume is very large, but the gas must first flow through the porous rock to the borehole and can only be injected and withdrawn slowly. For this reason, pore storage facilities are mainly used to compensate for seasonal fluctuations.

With a capacity of 3.9 billion m3 of natural gas, the pore storage facility in Rehden is the largest natural gas storage facility in Western Europe.

Example: With a working gas capacity of almost 4 billion m3 on an underground area of around 8 m2 , the Rehden gas storage facility is one of the largest pore storage facilities in Western Europe and has around one fifth of Germany's total storage capacity.

The future of hydrogen storage

Gas storage facilities will also play an important role in the energy system of the future: Surplus green electricity from volatile wind and solar energy can be converted into green hydrogen in a power-to-gas (PtG) plant and then fed into gas storage facilities.

On behalf of INES, the BVEG and the DVGW, a consortium of consultants led by the Gastechnologisches Institut gGmbH (DBI-GTI) has drawn up the study "Storing hydrogen - that much is certain". The study examined the technical possibilities of adapting current gas storage facilities to the use of hydrogen. The study is available for download here.

Conversion would probably be feasible for the majority of existing gas storage facilities, but new storage facilities would also have to be built. Both the conversion and the construction of new hydrogen storage facilities require long periods of around seven to ten years. When converting a gas storage facility to hydrogen, only around 20 % of the energy storage capacity can remain for technical reasons.

The HyCAVmobil research project in Rüdersdorf: EWE is currently testing the interplay between the injection and withdrawal of hydrogen from the underground cavern.

According to estimates, a total hydrogen storage capacity of 32 TWh can be provided from the current natural gas storage facilities in Germany. According to the BMWK's long-term scenarios, however, an additional capacity of up to 41 TWh is required. As the scenarios already envisage hydrogen storage capacities of 15 TWh in 2035, half of the existing potential would have to be reallocated within the next 12 years. Although the geological potential for this exists, there is a lack of a market framework for the commercial implementation of projects, among other things.

In addition, there are currently around 23 hydrogen storage projects, most of which are at an early stage without a final investment decision and have significantly smaller volumes than those required for commercial gas storage.

In total, investments of up to €12.8 billion will be required to develop the hydrogen storage facilities needed for the energy transition. Developing these storage facilities will be a major challenge for the storage industry and will require constructive cooperation with politicians and the relevant authorities.