FERC distributed energy resource technical report

A technical report by U.S. electricity regulatory staff assesses the potential reliability issues and likely benefits to the bulk power system resulting from an increased penetration of distributed energy resources. According to the report, increasing penetration of distributed energy resources may bring several associated reliability benefits to the bulk power system -- or could cause reliability concerns, if the resources are not properly accounted for.

Distributed energy resources, or DERs, have no single definition -- but they are generally conceived of as small, geographically dispersed electric resources, installed and operated on the distribution system at voltage levels below the typical bulk power system levels of 100kV. Historically, the term focused on generation like rooftop solar panels or on-site combined heat and power plants, but its meaning has broadened to include energy efficiency, microgrids, and even new technologies like energy storage. Distributed energy resources can be cost-effective alternatives to traditional utility infrastructure and business models.

Distributed energy resources installations have increased significantly in some regions of the United States in recent years thanks to factors including technology advances and state energy policies. In 2016, when distributed energy resources of all types accounted for about two percent of the nation's installed generation capacity, distributed solar photovoltaic (PV) installations alone represented over 12 percent of new capacity additions.  At the same time, regulators and industry participants are working to integrate these resources into the grid from engineering, reliability, and system planning perspectives.

In February 2018, staff of the Federal Energy Regulatory Commission published a report, "Distributed Energy Resources: Technical Considerations for the Bulk Power System." This report filed in Docket No. AD18-10-000 considers how the increasing penetration and integration of distributed energy resources in specific regions may affect bulk power system reliability. It summarizes technical assessments performed by Commission staff using industry power system models and commercially available power system simulation software "to identify the potential reliability issues and likely benefits to the bulk power system" from increasing distributed energy resource penetration. The study notes that its modeling of distributed energy resource capacity was "based on current trends for technology types, operational capabilities, and deployment distributions."

According to the report, greater penetration of distributed energy resources could have associated reliability benefits for the bulk power system. For example, by providing power close to the customer distributed resources can serve to reduce grid losses and reduce system peak load, or can serve as non-transmission alternatives that displace the need for more expensive wires upgrades.

At the same time, the report warns that "increasing DER capacity, if not properly accounted for, could cause reliability concerns for the bulk power system." It calls for improving and refining the data that is available for distributed energy resources for incorporation into planning and operating models, noting, "Collecting and using the most current and accurate data is key to getting a complete picture of how DERs affect the bulk power system."

The report identified key bulk power system reliability topics to explore in light of the growing adoption of distributed energy resources in the U.S., including:

• The impact of the current common industry modeling practice of netting DERs with load, which may mask the effects of DER operation;
• DER capabilities for voltage and frequency ride through during contingencies;
• The potential for improved voltages due to the unloading of the bulk power system associated with the location of DERs at or near customer loads;
• Potential effects upon system -wide transmission line flows and generation dispatch due to changing load patterns;
• The sensitivity of voltage or power needs to different types of DER applications (i.e., providing energy, capacity, or ancillary services);
• The need to develop planning processes that capture more detailed models of DERs and allow for modeling of the interface between the transmission and distribution systems to enable information exchange and more accurate calculations of the DER impact on the bulk power system; and
• The advantages and disadvantages of allowing DERs to participate directly in the organized wholesale electric markets.

The report also calls for continued examination of other issues, such as "sensitivities with higher DER penetration levels, changes in siting patterns, and potential impacts to the system’s response to events, disruptions and outages, including frequency events." It concludes, "Efforts such as these could help track and assess the impact of changing conditions on the bulk power system to identify emerging trends and address potential future reliability challenges."