Electrically Heated High-Temperature Thermal Energy Storage with Dual Operating Modes: From Concept to Validation

Abstract

The expansion of renewable energy sources and sustainable infrastructures for the generation of electrical and thermal energies and fuels increasingly requires efforts to develop efficient technological solutions and holistically balanced systems to ensure a stable energy supply with high energy utilization. For investigating such systems, a research infrastructure was established within the nationally funded project Energy Lab 2.0 including essential components for generation, conversion and storage of different energy sources. One element includes a thermal energy storage (TES) system based on solid materials, which was supplemented by an electrically heated storage component. Hereby, the overall purpose is to efficiently generate and store high-temperature heat from electrical energy with high specific powers during the charging period and provide thermal energy during the discharging period. Today’s solutions focus on convective electrical heating elements, creating, however, two major challenges for large-scale systems: limited load gradients due to existing systemic inertias and limited operating temperatures of 700 °C in the MW scale. To overcome such restrictions, a novel electrically heated storage component with dual operating modes was developed. The central component of this solution is a ring-shaped honeycomb body based on an SiC ceramic with electrical heating registers on the inside and outside. This configuration allows, in storage operation, instantaneous direct heating of the honeycomb body via thermal radiation. At the end of systemic start-up procedures, an operational change toward a convective heating system takes place, whereby the high-temperature heat previously stored is transferred to downstream components. The simulation studies performed for such a component show, for both operating modes, high operating temperatures of over 800 °C with simultaneous high electrothermal efficiencies of up to 90%. Experimental investigations on a 100 kW scale at the DLR test facility HOTREG in Stuttgart confirmed the feasibility, performance and good agreement with simulation results for a selected honeycomb geometry with a mass of 181 kg. With its successful testing and good scalability, the developed component opens up high use case potentials in future Power-to-Heat-to-Power applications, particularly for Brayton process-based Carnot batteries and adiabatic compressed air energy storage systems.