As mentioned in Part 1 of this blog, one cannot define the impact of distributed energy resources (DERs) without some form of assessment or study that can qualitatively or quantitatively provide a technical basis for that determination. Increasing levels of DERs will have a notable impact on BPS planning, operations, and performance during normal and abnormal system conditions. In many areas, transmission planning and operating entities are beginning to experience these effects at low DER levels. In contrast, some areas already have substantial penetrations of DERs and have been managing the system in the face of these impacts on a daily basis. It is critical to understand the impacts of increasing levels of DER under different conditions, and to develop appropriate solutions to the issues identified. The second half of this blog post presented here gives a very brief highlight to the various ways in which DERs may impact BPS performance; each should be considered individually yet all should be considered holistically as well.
Addressing DER Impacts to the Bulk Power System
The BPS must meet a set of performance requirements defined in various NERC Reliability Standards, which guide how the system is designed and operated within limits. To determine potential reliability risks, identify impacts to the BPS from aggregate amounts of DERs, and determine appropriate corrective actions (e.g., operating limits, transmission reinforcement, new BPS equipment, and reserve requirements), models need to accurately represent the expected future conditions. This requires accurate modeling of existing and expected DER penetrations into the planning horizon, similar to how demand levels are projected into the future and how new or retired BPS equipment is accounted for in future planning base cases. Without reasonable representations of DERs, understanding these impacts is infeasible.
Innovative solutions are being developed to address many of the impending issues associated with high penetrations of DERs and their impact to the traditional BPS and distribution systems in the planning and operations horizons. The table below illustrates examples of potential issues and possible solutions that may be considered. The solutions are wide-ranging and will fundamentally change how the BPS is planned, operated, and designed in the future. This will require all stakeholders working together to address any technical or regulatory roadblocks. This table generally focuses on impacts that will be observed in the near-term and mid-term horizons. Long-term issues and solutions will require a rethinking of many aspects of bulk power system planning, operations, and design in the future, including the investigation of grid-forming inverters.
What Needs to Be Done
Rather than rely on the impacts to determine when DERs should be represented in studies, we need the reverse: industry should be appropriately modeling aggregate levels of DERs to inform planning assessments of potential BPS impacts. Transmission planners should determine appropriate DER modeling practices and adapt those practices as DER levels increase. It is not reasonable to develop a bright line or uniform criteria for when impacts define when DERs should be modeled or considered in studies. Planners must execute planning assessments with a reasonable level of accuracy to ensure reliable operation of the BPS into the future.
Senior Manager, BPS Security and Grid Transformation, NERC