Whether steel, concrete or glass production: industrial production consumes more than 20 percent of the total energy requirement in Germany. To date, 90 percent of fossil sources have been used for this purpose. With the aim of making better use of renewable energies in these processes, researchers at the Karlsruhe Institute of Technology (KIT) are working on a globally unique high-temperature heat storage device using liquid metal technology.
The extremely conductive liquid metals could be heated to over 700 degrees Celsius using green electricity and flexibly store industrial heat. From April 22 to 26, 2024, the researchers will present a replica of their energy storage device at the KIT stand at Energy Solutions (Hall 13, Stand C76) at the Hannover Messe.
High-temperature thermal storage is currently being developed around the world to provide companies with resource-intensive production with heat independent of fluctuations in energy from renewable sources. For these storage systems, electricity is first converted into heat and stored. The heat is then used as needed, for example when electricity is more expensive and manufacturing processes need to continue. For many companies, the principle applies: the higher the stored temperature, the better – because this reduces the amount of additional energy that would be needed to reach the desired production temperature.
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In pilot plants, for example, liquid salts are used that can store temperatures of around 550 degrees Celsius. To achieve even higher temperatures, gases have so far been used: heated with electricity to around 700 degrees Celsius, they transport their heat to a storage material such as steel, volcanic stone or slag. “However, the hot gas does not transfer heat particularly efficiently to the storage material,” says Dr. Klarissa Niedermeier from the KIT Institute for Thermal Energy Technology and Safety.
Greentech x Hannover Messse: KIT is developing energy storage that can conduct heat 100 times better than liquid metal. Photo KIT
Liquid metals transport heat excellently
With her team, she is working on a novel solution for the high temperature range: a heat storage device in which lead-bismuth is used. “The thermal conductivity of this liquid metal mixture is up to 100 times higher than that of other heat transfer media used for storage,” says Niedermeier.
The high-temperature heat storage device is tested in a circuit: in a steel tank, the heated lead-bismuth seeps between ceramic beads that are approximately two millimeters small, to which it releases the heat. If the heat is needed again, the then “cold” liquid metal is passed through the beads again and heats up on them.
In simulations at KIT’s KALLA liquid metal laboratory, Niedermeier and her team have shown that the use of liquid metal can make charging and discharging the storage more efficient, especially if a very compact bed is used.
Efficient solution to store excess green electricity production
“When the liquid metal is heated with electricity from renewable sources, companies have an efficient solution to mitigate the fluctuations in the electricity supply from renewable sources and to store the clean energy easily, cheaply, quickly and at temperatures as close as possible to those of industrial processes,” says the researcher.
The process has huge potential for defossilizing the industry. Currently, 400 terawatt hours of heat per year are generated by industrial processes in Germany, 90 percent of which comes from fossil energy sources.
According to Niedermeier, the fact that liquid metals have hardly been considered for use in heat storage is mainly due to logistical reasons: there are only a few circuits worldwide to test such storage methods. The KALLA laboratory at KIT has a large cycle with lead-bismuth, which is used, among other things, for new projects in the field of renewable energies.
Presentation of the high-temperature heat storage at the Hannover Messe 2024
At the Hanover Trade Fair, the team is showing a replica of its heat storage device, which is about half the size of the actual experimental storage device at KIT.
This is designed for 100 kilowatt hours of heat and has so far been tested on a laboratory scale at temperatures of up to 400 degrees Celsius: “This is the first liquid metal heat storage of this type in the world with such a capacity. Our aim is to show that the principle works and has great potential,” says Klarissa Niedermeier. (ih)