Energy Storage Modeling for Distribution Planning

Storage is being proposed to solve many issues on the electric power grid, especially those issues related to renewable generation such as wind and solar generation. Some North American state and provincial regulators are requiring large amounts of storage to be installed to support anticipated needs of the power grid. Much of that new storage is expected to be connected to distribution feeders. Distribution planners lack tools and methods to assess storage impact on distribution system capacity, reliability, and power quality. Planners are accustomed to static power flow calculations, but accurate analysis of storage requires sequential-time simulation. This paper describes modeling storage for various types of simulations on distribution systems for different time frames typically involved. The basic impact on capacity and voltage regulation can generally be evaluated in simulations with 15-min to 1-h intervals. Evaluations of smoothing of renewable generation variations may require simulations with time step sizes of 1 min or less. Evaluations of such things as frequency control of microgrids and performance during transient disturbances will require dynamics analysis in intervals ranging from seconds down to microseconds. This paper is a summary of recent Electric Power Research Institute research in modeling energy storage for planning studies.