Design and management of hybrid electrical energy storage systems for regulation services

Regulation services (RS) play an important role in maintaining the stability of electric grids by correcting for short-term mismatches between electricity generation and demand. RS providers dynamically supply electricity to the grid or consume electricity from it, in response to regulation signals, in return for economic compensation. This capability is commonly realized through large-scale electrical energy storage (EES) systems based on batteries. However, the highly transient nature of the regulation signals implies that the batteries used for RS are subject to frequent charge and discharge cycles, leading to shortened battery life and thereby impacting the profitability of RS. In this work, we explore the use of hybrid EES (HEES) systems, which combine batteries and supercapacitors, to improve the profitability of RS. HEES systems have the potential to reduce the cost of providing RS by utilizing supercapacitors to respond to the high-frequency components of the regulation signal, prolonging battery life. However, realizing this potential presents several challenges. First, the benefits of HEES systems are profoundly impacted by the allocation of capacity to batteries and supercapacitors. This is because the reduction in battery replacement cost due to the use of supercapacitors must be traded off against the increased upfront cost for supercapacitors. Second, HEES systems introduce the problem of how to manage the power flows to the batteries and supercapacitors so as to realize maximum benefits. To address these challenges, we present a framework for the design and management of a HEES system, so as to maximize profit from the perspective of an RS provider. At design time, we propose a capacity optimization framework that determines the best allocation of capacity to batteries and supercapacitors. During system operation, the proposed management scheme selects how the different storage devices are orchestrated considering their characteristics, as well as the incoming regulation signal. Our experiments suggest that, with the proposed capacity optimization and management framework, the use of HEES systems can improve the profit of RS providers by 79%-196%.