Energy Storage
How a pipeline network for the transport of hydrogen can be used for energy storage.
Introduction
The energy transition poses many challenges, especially when it comes to storing and transporting renewable energy. Hydrogen as an energy carrier is coming more and more into focus. One interesting and increasingly discussed method is the storage of hydrogen in pipelines.
Basics of Hydrogen Storage
Hydrogen is a versatile energy carrier that can be produced in an environmentally friendly way through electrolysis - a process in which water is split into hydrogen and oxygen using electricity. Pressure tanks are ideal for storing this medium. This is due to the high energy density per unit mass (gravimetric energy density). This means that a significant amount of energy can be stored in a relatively small amount of matter.
Since tanks are often limited in size, the storage capacity is largely determined by the pressure under which the hydrogen is held in the tank. For example, Type 4 pressurized tanks are used in the automotive industry today, which guarantee an operating pressure of up to 700 bar.
A particular challenge posed by this storage option lies in the material properties of the tank and the properties of hydrogen itself. Hydrogen is the smallest known molecule and therefore has a high diffusion rate. This means that if the tank is improperly designed, the hydrogen will escape and the tank will be unsealed. In addition, in some materials (e.g. steel), hydrogen causes the material to expand, which reduces the life of the material if it is incorrectly designed. This is particularly the case when the storage is subjected to dynamic loads. Hydrogen embrittlement of materials is therefore a technical hurdle that requires special attention to ensure the long-term stability of the system.
Interim Summary
Hydrogen storage in pressure tanks offers an ideal possibility for energy storage. The most important parameters are the volume and the pressure difference. Special attention has to be paid to the diffusion as well as the hydrogen decomposition.
Pipeline Network for the Storage of Hydrogen
By limiting the tank volume, many hydrogen storage applications attempt to increase the pressure in the system and make the tank more resilient. However, increasing the operating pressure not only increases the storage capacity, but also the security concerns.
When using the pipeline network, however, the framework conditions are shifted due to the much larger volume potential. Distances of several thousand kilometers are considered realistic. For example, Robert Habeck, Germany's Federal Minister for Economic Affairs and Climate Change, announced the construction of a 10,000-kilometer hydrogen network in Germany by the end of the decade. Due to this enormous volume potential, the storage capacity, in contrast to conventional tanks, depends significantly on the length and diameter of the pipe. The pressure difference is still not negligible, but takes second place.
In addition, compared to tanks or electrical storage, the pipeline network offers greater flexibility to compensate for fluctuations in energy production and demand. By being able to store and withdraw hydrogen at different times, surpluses from renewable energy sources can be used effectively and a continuous supply can be ensured. This is essential for the stability of the energy network.
Unique Feature of the fiberior Pipeline System
As mentioned above, the biggest problems when designing a hydrogen tank or pipe are hydrogen vaporization, diffusion and pressure resistance. We have been able to solve these problems by selecting the right material and applying the appropriate know-how to the design of the pipe. On the one hand, we can minimize hydrogen diffusion by using polyamide materials, and on the other hand, we can exceed the operating pressure of alternative piping systems by using reinforcement fibers. At the same time, the materials we materials are not subject to hydrogen embrittlement, which has a positive effect on their service life.
The Future of Hydrogen as an Energy Storage System
In order to be able to better understand the potential of hydrogen pipelines as future energy storage, the following examples are used and compared with alternative storage options:
- Germany's largest offshore wind farm, Hohe See, produces up to 12.5 GWh per day. Flexible storage is particularly important when generating energy with the help of such plants, since production depends on the weather and does not follow the energy demand. In order to cover this capacity, a medium diameter (DN450) supply line was chosen between Berlin and Leipzig (170 km). The desired pressure increase is 250 bar. The chosen route is based on a study of the European Hydrogen Backbone, which is to be established to secure the hydrogen supply until 2040. Comparing this type of storage with Tesla Megapack battery storage, which can provide the required flexibility is a significant additional effort, as these must be built additionally for the pure storage. To achieve the required capacity, 3,277 packs are needed. This corresponds to additional costs of €5.2 billion, an area of 50,000 m² and 21 tons of raw materials per pack.
- At the end of 2022, the German Bundestag's Department of Economics, Transportation, Food and Agriculture presented a scenario in which Germany's electricity needs would have to be covered by energy storage for half a day on an average winter day. To put this into numbers, the daily consumption of a city like Hamburg can be used to calculate the number of inhabitants (7.7 GWh). Assuming the same parameters as before (pipe diameter 450 mm, pressure 250 bar), the required length is about 100 km. This corresponds to a planned supply line from Hamburg to Bremen. The same storage capacity can also be provided by a pumped storage plant. For example, the largest German pumped storage plant, Goldisthal (8.2 GWh), has a similar capacity. Over a period of 6 years, an area of 550,000 m² was converted with an investment of 623 million €. Here, too, the costs must be declared as additional investment.
Conclusion
Pipeline storage of hydrogen offers a promising way to meet the challenges of energy storage and maximize the use of renewable energy. Despite the technical and economic challenges that need to be overcome, this method has the potential to play a key role in the energy transition. With continued research and development, hydrogen storage in pipes can become a viable and sustainable energy solution for the future.