Evaluating the role of electricity storage by considering short-term operation in long-term planning

Short-term operating requirements and constraints in power systems are becoming increasingly important with the greater flexibility needed due to the integration of variable renewables. However, large problem sizes and computational barriers have limited the extent to which they are included in long-term planning models. Our objective is to understand the role of electricity storage in future renewable-based systems by including an accurate representation of short-term operation with high temporal detail within a long-term planning framework. Specifically, we discuss the development of a long-term investment model including a continuous relaxation of the technology-clustered formulation of the short-term unit commitment problem, including detailed operating reserve sizing and supply. This model is solved for a full year, and is applied to a test system with system load and renewable generation characteristics from the Belgian power system in a greenfield setting, i.e., assuming no pre-existing capacities, to analyze the role of storage at different renewable penetration levels. Both pumped-hydro storage and battery energy storage is considered, and their role in providing energy services and frequency control is investigated. We derive broadly applicable conclusions on the benefits and role of electricity storage to motivate why it may be built and operated. Results show that, in general, the integration of storage resources decreases total system cost, partially replaces flexible power plants, facilitates the integration of renewable energy sources, and allows inflexible technologies to perform better.