The key to security of supply: energy storage

Last winter, the media reported almost daily on the filling levels of German gas storage facilities. For the first time, the public became aware of the issue of storage facilities and their importance. Storage facilities are particularly important for the energy transition. In 2021 alone, 5.8 TWh of renewable energy was curtailed so as not to overload the grid. This corresponds to the annual electricity consumption of more than 1.5 million households.

Unlike electricity, hydrogen can be stored cost-effectively and, above all, for the long term. Storage facilities therefore play an important role in the future energy supply. For this issue on the subject of storage, we spoke to Boris Richter, Managing Director of STORAG ETZEL GmbH, the largest independent operator of cavern storage facilities in Germany.

NWN: We are currently storing large quantities of gas in underground caverns in Germany for the winter. In the future, we want to move away from natural gas or LNG and electrify as many processes as possible. Will we still need the cavern storage facilities to their current extent?

Boris Richter: The caverns have the task of storing energy, e.g. in the form of gas. It is precisely when large quantities of energy are drawn from the transmission grid, e.g. in winter, that the storage facilities provide additional support and cover peak demand by storing gas. The storage facilities have a buffer function. The import of energy, e.g. by sea via LNG tankers, also takes place intermittently, i.e. selectively over a short period of time. This means that cavern storage facilities are additionally required and must fulfill their function.

In future, the plan is to produce hydrogen from renewable electricity from the North Sea, which can then be stored in Etzel, for example. Why don't we store the renewable electricity directly in large batteries and feed the electricity into the grid later when we need it?

BR: In terms of efficiency, it makes perfect sense to store the electrons directly. However, the capacity of accumulators is currently far too small. A gas cavern with methane molecules can store one terawatt hour of energy. This can easily supply a small town with energy for a whole year. There are currently 51 gas caverns in operation in Etzel.

Hydrogen can also be stored above ground in mobile tanks. What is the advantage of underground storage?

BR: The volume of a cavern is much larger than an ordinary tank. On average, the caverns in Etzel are between 300,000 m³ and 600,000 m³ in size. The gas medium can be compressed with up to 200 bar and thus many millions of cubic meters of gas can be stored in a cavern. This would require many hundreds of tanks on the surface and therefore an enormous amount of space.

In future, you also want to store hydrogen in Etzel. Storag Etzel is already converting a cavern for this in the H2Cast project. Where do you currently stand with the project?

BR: We have just completed a positive leak test with hydrogen and will carry out further tests in the fall. Further construction work will be carried out above and below ground.

The majority of German hydrogen storage projects are located in Lower Saxony. Why are there so many storage facilities here in particular?

BR: Caverns are artificial cavities created by mining in salt formations. In addition to the technology, a salt deposit is therefore also required. These are usually salt domes or salt pillows. These salts were formed around 270 million years ago during the Permian period. A sea dried up in several stages and residual components of the sea, mostly salt, were deposited. The sea at that time was formed due to a basin structure, in the North German basin. This also provides us with a local reference. This is because around 70 percent of the salt deposits on land in Germany are located in northern Germany and largely in Lower Saxony. That is why there are many cavern storage facilities here in Lower Saxony, because there is a lot of salt under our feet.

What are the biggest challenges in the underground storage of hydrogen?

BR: We have to answer many technical questions, but also questions relating to licensing law. First and foremost, the safety and protection of the public, our employees and our plant are paramount. As we are a mining company, we are subject to mining law and our licensing authority is the LBEG in Clausthal-Zellerfeld. The mining authority is our supervisory authority and examines our applications very carefully.

Green hydrogen is to be imported to Germany for the first time via H2Global at the end of 2024. The first large-scale electrolysers will be connected to the grid in the coming years. Large quantities of hydrogen will soon be produced and landed in Lower Saxony. By when do we need functional hydrogen storage facilities?

BR: We assume that hydrogen storage facilities will be needed from 2027/2028 and that the market ramp-up for hydrogen will take place. However, this also means that the cavern storage facilities will also be connected to hydrogen pipelines. The infrastructure for this must be in place, otherwise storage facilities will not work. The pipelines are like lifelines in which the energy is transported.

In our future energy system based on renewable energies, we will need to store large quantities of hydrogen in order to guarantee security of supply. Assuming we convert all existing cavern storage facilities - would the current capacities even be sufficient for future storage requirements?

BR: If natural gas is to be completely replaced by hydrogen for industry and we assume that this will take decades, then the current storage capacity will not be sufficient. Because if you look at it in terms of energy, hydrogen has almost four times less energy than natural gas. This means that four times more storage volume is required to store the same amount of energy. It should also be borne in mind that, in addition to the hydrogen storage requirement, the storage cavity must also be provided, albeit at a decreasing rate for natural gas.

What order of magnitude are we talking about for future storage requirements?

BR: Current studies put the storage requirement for hydrogen in 2050 at 74 terawatt hours.

How long will it take to build up the corresponding capacities?

BR: In Etzel, we need around two to four years to convert existing caverns for hydrogen storage and a little longer to construct new hydrogen caverns in the salt dome at 24 newly planned locations. We already have the mining permits to build new caverns. In the coming years, we will be working with our partners in the H2CAST research project to prove that hydrogen can be stored in caverns without any problems. The project is funded by the state of Lower Saxony and the federal government.

Thank you very much, Mr. Richter.