The energy system is transforming a sustainable society. The overall targets include meeting climate goals and at the same time reaching energy independence. This chapter introduces the electric power grid as an infrastructure and enabler for reliable and sustainable electricity supply, including flexible grid infrastructure. It presents recently developed and implemented real-time operation models of Energy Management System (EMS) for control of Battery Energy Storage System (BESS). These models are needed to manage uncertain electricity loads, to deliver peak shaving and frequency regulation services and improve BESS financial viability. The delivery of these services results in economic return for the resource owner and increased flexibility for the grid. Implementation of storage systems also expedites the adoption of local electricity generation while also solving the challenges that this adoption on scale poses.