Energy storage systems are essential to secure a reliable electricity and heat supply in an energy system with high shares of fluctuating renewable energy sources. Thermal energy storage systems offer the possibility to store energy in the form of heat relatively simply and at low cost. In concentrating solar power systems, for instance, molten salt‐based thermal storage systems already enable a 24/7 electricity generation. The use of liquid metals as heat transfer fluids in thermal energy storage systems enables high heat transfer rates and a large operating temperature range (100°C to >700°C, depending on the liquid metal). Hence, different heat storage solutions have been proposed in the literature, which are summarized in this perspective. Based on these, future technical advances are suggested such as reducing the liquid metal share in the heat storage, using waste material as storage medium or using liquid metal as heat transfer fluids not only in sensible, but in latent or thermochemical energy storage systems. The use of waste material in a packed bed configuration with 5% porosity, for example, can bring down the storage material costs to 2%–3% of the costs of a liquid metal‐only storage system. Furthermore, future application fields beyond concentrating solar power are proposed: supply of industrial process heat, waste heat integration and power‐to‐heat‐to‐power processes.

Thermal energy storage systems for high temperatures >600 °C are currently mainly based on solid storage materials that are thermally charged and discharged by a gaseous heat transfer fluid. Usually, these systems benefit from low storage material costs but suffer from moderate heat transfer rates from the gas to the storage medium. Therefore, at the Karlsruhe Liquid Metal Laboratory, liquid metals are investigated as alternative heat transfer fluids for such heat storage systems, making use of the broad temperature range, in which the metals are in a liquid state, and their efficient heat transport capabilities. In this work, the design and construction of a high-temperature test rig using liquid lead is presented. The goal of the experiments is to demonstrate the operability of a pump, valves and measurement equipment at 700 °C in a challenging corrosive environment. Based on material pre-tests in stagnant lead at 700 °C, which are also shown in this study, aluminizing and pre-oxidation of the pipes and components are applied for enhanced corrosion protection.

Liquid metal packed‐bed thermal energy storage (TES) can improve industrial waste heat recovery due to its wide operating temperature range and high thermal conductivity. However, reducing costs, especially for storage media, is essential for broader adoption. Until now, no experimental analysis of low‐cost material in contact with liquid metal at high temperatures has been investigated in detail. Therefore, this study focuses on natural and waste materials as packed bed materials for high‐temperature TES systems using lead as the HTF. Two steel slags (from an electric arc furnace and a basic oxygen furnace) and four natural materials (basalt, red brick, iron pellets, magnetite) were selected as promising candidates due to suitable thermal properties and low material costs. They were exposed to static lead at 750°C for 1008 h to assess their compatibility with the HTF. After exposure, all samples showed degradation or phase transformation. Steel slag performed best with only minor lead attack on the Mg‐Fe oxide phases. Diopside in basalt was concluded to be stable in lead, but nepheline, also present, appeared to have reacted with Pb. In brick, the main component, quartz, was found to be stable in lead, but impurities and trace elements in the sample reacted with lead. Magnetite and iron pellets had the most severe degradation, forming deep cracks due to phase transformation at high temperatures.

Conventional routes for the production of formaldehyde rely on the use of methanol and air, with the presence of catalysts such as silver or mixed‐metal oxides. These processes are highly energy intensive and therefore raise concerns in terms of cost‐effectiveness and environmental impact. In that respect, sodium or sodium compounds are more favorable as catalysts for the direct dehydrogenation of methanol to water‐free formaldehyde. A method is presented for the coproduction of hydrogen and anhydrous formaldehyde – both valuable products – on the laboratory scale, with a particular focus on the design and testing of a sodium vapor catalyst dosing unit that enables the process to be performed continuously.