In the quest for more efficient and sustainable energy solutions, researchers have been exploring various methods to optimize thermal energy storage (TES) systems, crucial components in concentrating solar power (CSP) plants. A recent study led by Antonio Soria-Verdugo from the Thermal and Fluids Engineering Department at University Carlos III of Madrid sheds new light on the performance of sensible heat TES systems, comparing granular materials and solid blocks during the discharge process.
The study, published in Applied Sciences, delves into the intricacies of TES systems, which are essential for storing excess heat generated during peak solar hours and releasing it when solar irradiation decreases. This capability is vital for maintaining stable and efficient power generation in CSP plants. “The efficient operation of TES systems may allow operation of the power block of the plant under uniform and stable conditions, inducing efficient conversion of thermal to mechanical power in the turbine during the power cycle, leading to an increase in the overall efficiency of the plant,” Soria-Verdugo explains.
The research focused on two primary types of TES systems: those using granular materials and those using solid blocks, specifically alumina. The granular material TES system was studied in two configurations: a fluidized bed and a confined bed. The fluidized bed, where the granular material is freely moving, showed a homogeneous temperature distribution but required a significant pressure drop to circulate the heat transfer fluid (HTF). In contrast, the confined bed, where the granular material is mechanically restricted, exhibited thermal segregation with a clear thermocline separating hot and cold zones. This configuration maintained a higher and more uniform HTF outlet temperature during the discharge process.
The alumina block TES system, on the other hand, demonstrated a much lower pressure drop, making it more energy-efficient in terms of HTF circulation. However, it showed a more diffuse temperature variation zone compared to the confined-bed system. “The pressure drop required to circulate the heat transfer fluid (HTF) through the TES system made of alumina blocks was measured to be two orders of magnitude lower than that used in the granular material TES system,” Soria-Verdugo notes.
One of the most compelling findings was the exergy efficiency of the confined-bed TES system, which remained above 90% throughout the discharge process. This high efficiency, combined with the system’s ability to supply HTF at a uniform high temperature, makes it a strong contender for commercial applications in CSP plants. The study’s results suggest that confined-bed TES systems could be the key to enhancing the overall efficiency and stability of CSP plants, potentially leading to more reliable and cost-effective renewable energy solutions.
This research not only advances our understanding of TES systems but also paves the way for future developments in the field. As the energy sector continues to seek more sustainable and efficient solutions, the insights gained from this study could influence the design and implementation of TES systems in CSP plants worldwide. By optimizing the discharge process and enhancing exergy efficiency, researchers and engineers can work towards creating more robust and efficient energy storage solutions, ultimately contributing to a greener and more stable energy future.
