Source: Energy & Management Powernews, October 24, 2022
For the demand-driven provision of H2, gas storage facilities are important. Especially German underground storage facilities could turn into the H2 storage focus in Europe, finds Storengy.
In view of the upcoming winter months, all eyes in this country are currently on the levels of German natural gas storage facilities. There are about 50 underground natural gas storage facilities in Germany according to the latest available publication of the Mining Office of Lower Saxony. When they are 100% full, they hold around 24 billion m3 of gas, which is roughly equivalent to 27% of Germany's annual consumption. Even though they hold an increasingly uneconomical fossil fuel - especially against the backdrop of the current energy crisis - natural gas storage facilities are anything but a discontinued model. Quite the opposite, finds Catherine Gras, CEO of Storengy Germany and Storengy UK, two companies of the French "ENGIE Energy Solutions International" group (Engie).
The storage service provider, headquartered in Berlin, has six storage sites in Germany. The company states its usable gas volume for the year at 1.6 billion m3. Storengy is currently examining the new construction of one to two salt caverns at its Harsefeld site (Lower Saxony) not far from Hamburg - 30 to 100 million m3 of hydrogen could be stored there in the future. The plans are currently still on paper as part of a feasibility study. Detailed statements on it, one can make only after conclusion of the study in presumably two months, explains the manager.
Only so much: "The work so far shows however already the necessity of a co-ordinated structure of the future hydrogen infrastructure", so grass with view of the natural gas networks and - storages. The CEO roughly expects pure hydrogen to be stored in Harsefeld from the beginning of the next decade.
Even in an energy system that is to be based largely or entirely on renewable energies, the storage of hydrogen generated by surplus green electricity is the "safest and most economical solution," the CEO asserts. Above all, in a 100% renewable energy power and heat system, controllable residual power plants will be needed, Gras says, referring to gas-fired power plants. Today mainly operated with natural gas, in the future increasingly with hydrogen and biomethane, these could step in flexibly to bridge dark slack periods.
Cavern storage versus pore storage
The manager attests to good geological conditions for underground storage in northwestern Europe and therein in particular Germany. Basically, a distinction is made between two types of underground storage: on the one hand, artificially created cavities in salt domes created by flushing out the salt, so-called cavern storage. On the other hand, naturally occurring, porous rock, such as water-bearing aquifers or former gas and oil reservoirs in permeable rock formations, so-called pore reservoirs.
The Storengy manager sees the salt domes in the ground of the North German lowlands in particular as predestined for underground storage. "According to the current state of research, we assume that cavern storage facilities are better suited for hydrogen storage due to their geology." Gras is getting support from the Berlin-based Initiative Energien Speichern e.V. (Ines).
According to Ines, the petrochemical properties of the salt guarantee a natural seal for the rock salt caverns and make an additional lining unnecessary. At depths of 800 to 1,500 meters, maximum pressures of up to about 200 bar are possible. The consequences: Not only can large quantities of gas be stored in caverns, the gas can also be injected and withdrawn quickly. Short-term, high demand fluctuations can thus be flexibly compensated.
In a one hundred percent electricity and heat system from renewable energies, however, the other type of underground storage facility, the pore storage facility, will also be needed, notes Catherine Gras. This involves injecting gas under high pressure into underground storage rock. However, these reservoirs are slower in the process of injection and withdrawal compared to caverns. For background information: In pore storage facilities, large volumes of gas are stored in widely distributed pores at lower pressure. Therefore, injection and withdrawal can only be slower. Above all, the seasonal fluctuations in gas demand can be balanced out with the help of pore storage systems, especially since these usually have much larger capacities.
Avoiding potential embrittlement
As a result of the envisaged cyclical injection and withdrawal of hydrogen underground, Storengy sees particular challenges for the materials used. Especially in the selection of steels, elastomers and cements, potential embrittlement due to penetration of the small hydrogen molecules must be prevented, he said. Particularly in the case of pore storage systems, the Storengy boss fears interactions of the hydrogen with certain rock layers or microorganisms.
She refers to the still ongoing research project "RINGS" (Research on the Injection of New Gases in Storages). In this, Storengy is working with French partners - the University of Pau and gas storage operator Terega - to investigate the behavior of hydrogen when mixed with natural gas underground. Using rock samples, microorganisms, storage water and variable compositions of gas, they are reproducing reservoir conditions to study the behavior of the reservoir's porosity at different hydrogen concentrations to determine the highest possible concentration.
Green hydrogen preferred
When it comes to the color, i.e. the way the hydrogen is produced, the Engie subsidiary is clearly going green. One source for the regeneratively produced hydrogen is to be the "HyNetherland (HyNL)" project in Eemshaven, a seaport in the northeast of the Netherlands, not far from the German border. There, parent company Engie is building a gigawatt-scale green hydrogen value chain. By 2025, the French utility plans to build a 100 MW electrolyzer fed by offshore and onshore wind power. In 2030, its capacity is to be increased to 850 MW, after which a further expansion up to 1,850 MW is targeted.
In addition to being used in the chemical industry, the green hydrogen is also to be fed into the planned hydrogen backbone network, which will be based on Gasunie's converted gas network. As Storengy CEO Gras assures, the green hydrogen produced in Eemshaven will also be exported to Germany. But "the import of green hydrogen by sea via the ports of northern Germany will also require storage capacities to bring delivery and consumption into line," she predicts.
For a rapid ramp-up of the hydrogen economy, Gras still sees a number of building blocks on the part of policymakers. On the one hand, a reliable market environment is needed for investors, suppliers and potential customers. On the other, efficient approval procedures would have to ensure that there are no unnecessary delays in the development process. Gras: "If we succeed in this, we will be a big and important step closer to helping hydrogen achieve a breakthrough."
Author: Davina Spohn
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