(567f) Design of a Pumped Thermal Energy Storage (PTES) System Capable of Delivering High-Grade Heat

Pumped thermal energy storage (PTES), which stores electrical power as heat, is a promising approach for long-duration energy storage. PTES systems can enhance the reliability, stability, and effectiveness of renewables-rich power systems. While charging, a PTES system runs as a heat pump with surplus electricity, which: (i) supplies heat to a hot store, creating a high-temperature reservoir, and (ii) producing a cooling effect in a cold store, forming a low-temperature reservoir. When electricity is needed, the PTES system can be reversed and function as a heat engine. This technology can address not only the inherent intermittency of renewable sources, which most long-term energy storage technologies can address, but also address the need for decarbonizing heat. Heat demand comprised 48.7% of the global energy demand in 2020 but renewables accounted for just 12% of this heat demand [1][2]. This highlights the need for research into expanding decarbonized heat supply. In this work, we propose an augmented PTES system, capable of delivering both electricity and heat while maintaining consistent operation in both modes. This is accomplished through careful management of the state-of-charge of the storage media and addition of balancing heat exchangers. The basis of the PTES system lies in a supercritical CO₂ Brayton cycle which has been investigated thoroughly in recent studies [3].

The system is shown in Figure 1a. The overall process was built on previous work by the authors is explained in greater detail in [4] and [5]. The methodology of the process design involves implementing state-of-charge management into each cycle’s design. The goal of this is to maintain equal SoC at both the hot and cold storage tanks. This is done through an algorithm outlined in Figure 2. When the system is designed according to this flowchart, the rate of change in both tanks are always equal. However, this only holds for electrical charge and discharge. When the system is used to supply heat from the hot reservoir, this balance is broken. Thus, there is a need for maintaining this balance externally. This is done in through a balancing heat exchanger that uses excess hot storage media to heat up unused cold storage. The augmented process is shown in Figure 1b, for a side-by-side comparison with the base case. This process can then be used to provide heat to a coupled industrial process, provide district heating or the heat can be sold. Heat integration increases the overall efficiency of the storage plant by 35% while also providing renewable-based heat supply.

References

[1] REN21, “Renewables 2023 Global Status Report,” REN21, Paris, 2023.

[2] IEA, “Renewable heat – Renewables 2022 – Analysis,” IEA, 2022. https://www.iea.org/reports/renewables-2022/renewable-heat.

[3] Marchionni, G. Bianchi, S. A. Tassou, Review of supercritical carbon dioxide (sco2) technologies for high-grade waste heat to power conversion, SN Applied Sciences 2 (03 2020). doi:10.1007/s42452-020-2116-6.

[4] Zhu, A. Albay, M. Mercangoz, “Pumped Thermal Electricity Storage: Modelling of a Reversible Recuperative sCO2 Pumped Brayton Cycle for Variable Power Operation”, presented at the AlChE Annual Meeting, Orlando. FL, November 2023

[5] A. Albay, Z. Zhu, and M. Mercangöz, “State-Of-Charge (SOC) Management of PTES Coupled Industrial Cogeneration Systems,” in Turbo Expo 2024, ASME, Jun. 2024.