The ongoing transition toward renewable energy sources brings with it a major challenge: strong fluctuations in electricity generation. Therefore, the need for efficient and flexible energy storage solutions becomes increasingly urgent. High-temperature thermal energy storage offers a promising solution to this issue.

Rather than relying on entirely new power plant concepts, retrofitting existing fossil-fired fluidized bed power plants with high-temperature thermal energy storage systems offers a particularly attractive pathway. This approach keeps existing infrastructure in productive use, cutting investment costs and avoiding the costly and resource-intensive disposal of still-valuable power plant assets. At the same time, it enables a transition toward flexible, CO₂-free operation.

The required modifications to existing fluidized bed power plants are identified and investigated using a pilot-scale thermal energy storage testing unit, which enables experimental charging and discharging cycles to demonstrate long-term operability. During charging, renewable electricity is used to heat air, transferring thermal energy to a bed of solid particles that serves as the storage medium. In discharge mode, the stored heat is released by passing cold air through the heated particles, generating hot air that is subsequently used to produce superheated steam in a water–steam cycle. To support the design and evaluation of this concept, numerical models are developed and rigorously validated against experimental data from the pilot unit. These models are applied to optimize plant modifications, and the overall concept is assessed in terms of electrical efficiency, economic viability, as well as environmental and social impacts.