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How utilities and state regulators can adopt a modern, risk-informed approach to mitigate unintentional islanding risks.

As the adoption of inverter distributed energy resources (DERs) like solar and energy storage systems accelerates, utility concerns regarding unintentional islands (UIs)—which occur when a segment of the electric grid remains energized by a DER for a period after being electrically isolated from the rest of the grid—have led to the development of several grid protection strategies to mitigate risks and maintain system safety and reliability.

One common yet heavily-disputed strategy, which has increasingly been required by utilities, is direct transfer trip (DTT). DTT is a protection system that uses a direct, point-to-point communications link between geographically separated equipment to quickly disconnect and stop DERs from generating after they have been electrically isolated from the main utility grid. However, DTT is significantly more expensive than other mitigation strategies and can threaten the financial viability of both individual DER projects and entire clean energy programs.

A forthcoming study by IREC evaluates the various utility justifications for requiring DTT, analyzes the risk of UI (leveraging new modeling and probability analysis), critiques existing utility screening practices, and outlines a suite of alternative grid protection strategies that can effectively address grid safety and reliability concerns for inverter DERs.