Anti-islanding detection methods are how an inverter senses that the utility is gone, so it can stop feeding a section of grid that has been cut off. The risk is highest when the load in the cut-off section roughly matches the power the PV or battery system is feeding in at that moment. Active methods, such as Sandia Frequency Shift, apply a small, continuous disturbance to the inverter output. While the grid is present, the disturbance has no effect on it. In one vendor's version, the inverter adds a little reactive power, which acts as a phase shift. Positive feedback then pushes the frequency up or down until a frequency trip limit is reached, but only if the grid is absent. Passive methods leave the grid alone and only watch it. For example, they trip when the frequency changes by a set amount within a set time. IEEE 1547 and UL 1741 require islanding detection and test for it, but they do not say how detection must work, so vendor schemes vary and can interfere with each other. Ride-through functions mean low voltage can no longer be used to detect an island. Direct transfer trip is a communications-based fallback when inverter detection is not enough.
<!-- review notes
related_toc1 drafted · lead Anti-islanding
Detection methods are the mechanisms inverters use to carry out the anti-islanding function.
sec=4.3.5.8 h=0943b61c4b74sec=2.1 h=498d60cb2f86sec=5.4.5.1 h=90742956f36aUnintentional islands can form when the load in the disconnected section roughly matches the PV or storage feed-in power.
sec=4.3.5.8 h=0943b61c4b74sec=14.2.2.5 h=39500d616e75sec=2.1 h=498d60cb2f86verified by: review-workflowverified on: 2026-10-24
c3 drafted · lead IEEE 1547 proposed
IEEE 1547 sets the island detection requirements but does not specify the detection mechanism, so vendor schemes vary and are often proprietary.
sec=4.3.5.8 h=0943b61c4b74c4 drafted · lead UL 1741 proposed
UL 1741 listing includes an unintentional islanding test of the inverter.
sec=4.3.5.8 h=0943b61c4b74sec=5 h=ea5c57c87656c5 drafted · lead Sandia National Laboratories
Several common active methods are named after Sandia: Frequency Shift, Voltage Shift and Impedance Shift. A Sandia report also defines the method groups used in utility questionnaires.
sec=5 h=ea5c57c87656sec=5.4.5.1 h=90742956f36areview note: support check: partial - Passages show Sandia Frequency Shift and the Sandia report groups, but Sandia Voltage Shift and Impedance Shift appear only as named options in a questionnaire, not as common methods.
c6 drafted · lead Frequency trip
In the frequency-shift method, positive feedback pushes the frequency until it reaches the low or high frequency trip limit, and the inverter then disconnects.
sec=5 h=ea5c57c87656c7 drafted · lead Low-voltage ride-through
Ride-through means low voltage can no longer be used to detect an island, which may make an unintentional island more likely.
sec=4.3.5.8 h=0943b61c4b74c8 drafted · lead Direct transfer trip proposed
A communications-based alternative when inverter anti-islanding is missing or not sufficient. It is often expensive because it needs protection-grade communication channels.
sec=4.3.5.8 h=0943b61c4b74c9 drafted · lead Tesla Megapack 2 proposed
Uses active Sandia Frequency Shift anti-islanding and trips within 2 seconds of the island forming.
sec=5.4.5.1 h=90742956f36areview note: support check: partial - The passage says Megapack uses active Sandia Frequency Shift and trips within 2 s, but it doesn't name the Megapack 2 model specifically.
c10 drafted · lead Tesla Megapack 2 XL proposed
Uses active Sandia Frequency Shift anti-islanding.
sec=5.4.5.1 h=90742956f36areview note: support check: partial - The passage covers Megapack generally with active SFS, without naming the 2 XL model specifically.
c11 verified · fact Tesla Powerpack 2 proposed
Uses active Sandia Frequency Shift anti-islanding.
sec=h72 h=c4eb27777801verified by: review-workflowverified on: 2026-10-24review note: support check: partial - The passage gives active SFS for 'the inverter' without naming Powerpack 2.
c12 drafted · lead Sunny Boy Smart Energy US-50
Its active anti-islanding method is frequency shift.
tbl=57.r11 h=2954afd669b0c13 drafted · lead Sunny Central UP-US
Can be ordered with passive islanding detection based on rate of frequency change. This function is not UL-certified.
sec=14.2.2.5 h=39500d616e75review note: support check: partial - The passage supports optional passive detection based on rate of frequency change and no UL certification, but it doesn't name Sunny Central UP-US.
c14 drafted · lead CPS SCA100K-T-US-480 / SCA50K-T-US-208
Uses the Group 2A islanding detection method with a stepped perturbation. Other CPS three-phase models use Group 1 with a continuous perturbation.
sec=5 h=ea5c57c87656sec=11 h=b8f15559c62dc15 drafted · lead CPS SCH200K-T-US-480 / SCH250K-T-US-600
Uses the Group 2A islanding detection method with a stepped perturbation.
sec=5 h=ea5c57c87656sec=11 h=b8f15559c62d