Optimization-based state-of-charge management strategies for supercritical CO2 Brayton cycle pumped thermal energy storage systems
Alp Albay, Zhennan Zhu, Mehmet Mercangöz
Abstract
We present a study concerning the state-of-charge (SoC) management strategies for pumped thermal electrical energy storage (PTES) systems. The particular system under study is a recuperative Brayton Cycle PTES with supercritical CO 2 as the working fluid and uses molten salt and water as hot and cold side thermal storage reservoirs. The charging and discharging cycles, including the turbomachinery, heat exchangers, and two-tank thermal storage units are modelled using Aspen HYSYS, considering variable speed operating characteristics of the turbomachines. An in-cycle SoC management strategy is proposed to maintain equal charging and discharging capacities between the hot and cold side thermal storage reservoirs, whereas a cycle-to-cycle SoC management strategy is used to constrain the PTES operating envelope for charge/discharge power and duration given operational objectives. The model is used in several case-studies to demonstrate the SoC management strategies. The case study results showed that, given an electricity price profile, the algorithm can determine feasible charge/discharge profiles while maximizing the operational profit. Additionally, if the PTES system is integrated with a wind farm, it enables the wind farm to provide dispatchable power. The round-trip efficiencies of the system is within the range of 35–60 % and in certain scenarios with increased part-load operation, such as the wind farm integration scenario, the average efficiency is observed to be 46.5 %. The SoC of both tanks displayed a negligible deviation of 0.24 % after five days of operation, including operation under part load conditions. The findings provide a new avenue for revenue stacking via flexible operations and can help accelerate the adoption of PTES systems. • Analysis of part-load performance of a recuperative SCBC PTES system • A SoC management strategy for the PTES system to be used in operation scheduling • Demonstrate the ability of the proposed algorithm by optimizing operational profit • Highlights potential of PTES systems to provide dispatchable renewable power