Cryo

Why hydrogen?

Germany is an energy importing country and will probably have to obtain a considerable proportion of the energy it needs from abroad in the future. The established import routes mainly use energy sources in which the energy is chemically bound. These energy sources are either already in liquid form or are specifically liquefied in order to enable economically and energetically efficient use along the entire value chain. Current research and development is focusing in particular on hydrogen, especially liquefied hydrogen (LH2 for liquid hydrogen). This energy carrier does not contain any carbon-containing compounds and therefore cannot cause any climate-damaging CO₂ emissions. This property makes it a promising candidate for a sustainable energy future.

How cryo-TEG works

In order to be able to use hydrogen in primary energy converters such as combustion engines or fuel cells, it must first be heated and vaporized. Current systems use the waste heat from the cooling water for this purpose. In future, this function could be performed by a cryo-thermoelectric generator (cryo-TEG).

How a cryo-TEG works - Image source: DLR

Such a thermoelectric generator offers the great advantage that, in addition to providing heat, it also generates electrical energy. For this purpose, thermoelectric modules convert the waste heat extracted from the cooling water into electricity. The heating ensures a continuous supply of gaseous hydrogen to a fuel cell or hydrogen engine. In addition, the cryo-TEG relieves the coolant circuit, which offers considerable advantages, especially for drives with fuel cells. The electrical energy fed in increases the efficiency of the hydrogen application and reduces both hydrogen consumption and operating costs.

Project goals

The aim of the project is to investigate cryo-TEG technology in collaboration with Daimler Truck AG. The development of heat transfer structures and the selection of high-performance thermoelectric modules are particularly challenging, especially considering the extremely low temperatures of down to -253 °C.

Commercial vehicle with integration of a cryo-TEG on the LH2 tank Image source: DLR

The system is designed using validated simulation models and based on previously characterized thermoelectric modules. After a successful virtual concept phase, a generic functional model is built and then measured on a specially developed cryogenic test bench. This functional model is designed both in terms of measurement technology and construction in such a way that the results can be transferred to various hydrogen applications. As part of the collaboration with Daimler Truck AG, the focus is on the application in commercial vehicles. To this end, a 1-D model of the LH2 system and the cost-benefit-optimized cryo-TEG is being developed. This model is used to estimate and evaluate the potential of the cryo-TEG based on real driving data. Specifically, this means that the electrical energy provided by the TEG and the hydrogen saved are quantified. From this, it is ultimately possible to derive the potential for increasing efficiency and reducing costs that can be achieved by using the cryogenic TEG.

Our project partners