LH2-Flatlight- Holistic concept development of flat liquid hydrogen tanks

Fiber-reinforced plastics (FRP) are the preferred choice for hydrogen tanks due to their excellent strength-to-weight ratio. However, today's tanks for gaseous, compressed hydrogen are spherical or cylindrical and therefore severely constrained in their geometry. They cannot be used flexibly enough for future vehicle architectures.

The LH2-Flatlight project aims to develop flat and lightweight thermoplastic tanks for the storage of liquid hydrogen. With a flat tank it is possible, for example, to store the hydrogen in the underbody of the vehicle without losing storage space. For this purpose, different design concepts (Figure 1) are analyzed and evaluated in order to finally develop the most suitable tank concept in detail. In a first step, the concepts are roughly structured on the basis of given framework conditions and design specifications. These are then structurally analyzed using FEM (Finite Element Method) and suitable manufacturing concepts are developed. The structural analysis (see Figure 2) is used to assess the strength of the tank and to identify potential weak points in the design. Particularly critical areas are the ribs, which prevent the tank from buckling, and the dome cap. These will be specifically analyzed as the project progresses.

The storage of hydrogen under cryogenic conditions places high demands on the materials used. In particular, the large temperature fluctuations from about -250°C during filling to +70°C during operation subject the materials to considerable stress. These extreme conditions can favor the formation of microcracks which can lead to leaks and thus to failure of the tank at high load changes. The characterization of the material behavior at low temperatures therefore plays a central role in the project. The aim is to optimize the design to avoid thermomechanical failure.

Specialized measuring methods are used to investigate the material properties including methods already available at the institute, such as X-ray microscopy, and new technologies acquired as part of the project, such as a permeation measuring cell. These methods allow the targeted analysis of microcrack formation and hydrogen permeation resistance of materials.

The LH2-FlatLight project is funded by the State of Rhineland-Palatinate through the Ministry of Science and Health (funding reference 724-0027#2023/0003-1501 15404).