Solar Plant Modeling Impacts on Distribution Systems PV Case Study

With the vast increase of distributed energy resources (DER) on utility systems not only due to renewable portfolio standard requirements but also the potential to delay distribution upgrade expenditures, the distribution engineer is confronted with the very challenging task of fulfilling the scope of a system impact study to determine if there exists potential for the DER to create any adverse operational or voltage issues, both now and in the future as system changes occur. Fortunately, there are industry standards and guides that describe how to fulfill the technical study requirements with some step-by-step guidance. The complexity of the system impact study also depends heavily upon the type and size of DER, its operating modes. An all-encompassing study might cover a vast number of areas with just a few of these being voltage and stability analysis, harmonics, transients, distribution system protection, and DER relaying requirements. Predicting PV generation profiles for different seasons and hours of the day rests heavily on the plant design and layout. Ways to determine those load levels will be discussed. Distribution system and PV inverter modeling complexities will be presented, along with why they are important for impact studies. An actual field installation of a large PV plant will be used to evaluate some distribution system impact issues, with a focus on loading scenarios and voltages. Various operating modes of inverters will be discussed with focus on how they may help or hinder the operation of the system. These operating modes and their effects on voltage regulating device interactions will be presented to demonstrate how more commonly used regulator control settings without DER may cause voltage violations with DER.