(313i) Providing Ancillary Services through Optimal Operation of Pumped Thermal Energy Storage Systems.

Presently, long-duration energy storage systems can address long term variabilities in RE supply and energy arbitrage, but ancillary services offer an important and often necessary value stream. Studies on pumped hydro storage [2], solar thermal plants [3] and wind farms coupled with battery storage [4] have demonstrated that ancillary services can be profitable in addition to the regular operation of the plants. Most often, these services require off-design or part-load operation of energy storage systems.

One such class of energy storage systems is Pumped Thermal Energy Storage, where excess energy is stored in thermal reservoirs with the aid of heat pumps during charging and recovered with heat engines during discharging. With both energy arbitrage and ancillary services capabilities, they are becoming a highly appealing solution for greater integration of variable renewable energy sources into the electricity grid [5]. This study builds on a previous part-load design and optimization study of a PTES system by adding ancillary services capabilities to the operation of the PTES system [6]. In addition to capacity value and energy arbitrage, other grid services such as secondary frequency regulation, spinning reserve and voltage support are considered in this study. The extreme power variability of the PTES system and the decoupling of the powertrain with the storage equipment provides the flexibility required for these services.

The existing scheduling optimization problem is augmented to include the grid services mentioned. The optimization formulation presented here incorporates capacity value and spinning reserve as a lower bound for operating power and state-of-charge respectively, whereas secondary frequency regulation related service is a constraint on the nominal operating power. The objective function maximizes the operating profit, given an electricity price and frequency requirement profile. The current study shows that PTES systems, using the proposed dispatch methodology, can participate in both energy arbitrage markets and ancillary services markets effectively.

References

[1] P. Makolo, R. Zamora, and T.-T. Lie, “The role of inertia for grid flexibility under high penetration of variable renewables - A review of challenges and solutions,” Renewable and Sustainable Energy Reviews, vol. 147, p. 111223, Sep. 2021, doi: 10.1016/j.rser.2021.111223.

[2] X. Ma et al., “Optimizing pumped storage hydropower for multiple grid services,” Journal of Energy Storage, vol. 51, p. 104440, Jul. 2022, doi: 10.1016/j.est.2022.104440.

[3] M. Koubar, O. Lindberg, D. Lingfors, P. Huang, M. Berg, and J. Munkhammar, “Techno-economical assessment of battery storage combined with large-scale Photovoltaic power plants operating on energy and Ancillary Service Markets,” Applied Energy, vol. 382, p. 125200, Mar. 2025, doi: 10.1016/j.apenergy.2024.125200.

[4] M. Naemi, D. Davis, and M. J. Brear, “Optimisation and analysis of battery storage integrated into a wind power plant participating in a wholesale electricity market with energy and ancillary services,” Journal of Cleaner Production, vol. 373, p. 133909, Nov. 2022, doi: 10.1016/j.jclepro.2022.133909.

[5] S. Sharma and M. Mortazavi, “Pumped thermal energy storage: A review,” International Journal of Heat and Mass Transfer, vol. 213, p. 124286, Oct. 2023, doi: 10.1016/j.ijheatmasstransfer.2023.124286.

[6] A. Albay, Z. Zhu, and M. Mercangöz, “Optimization-based state-of-charge management strategies for supercritical CO2 Brayton cycle pumped thermal energy storage systems,” Journal of Energy Storage, vol. 111, p. 115387, Mar. 2025, doi: 10.1016/j.est.2025.115387.