Does solar work in a power outage? Why grid-tied panels shut down

A house with solar panels on the roof goes dark in an outage along with the rest of the street, and the homeowner reasonably asks what they paid for. The answer is not a defect and it is not a conspiracy by the utility. It is a written requirement, it is in a document with a number, and the inverter is doing precisely what it was certified to do.

This page covers why, what changes it, and the one narrow exception. Every requirement quoted below comes from a published standard or a government or industry document that quotes it, and every product statement comes from a manufacturer datasheet. We have not tested any of these products.

The requirement, quoted

The governing document is IEEE 1547-2018, the Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces. Its Clause 8.1 covers unintentional islanding. The Massachusetts Technical Standards Review Group, which publishes the required IEEE 1547-2018 settings for New England utilities, quotes the operative sentence directly:

Per IEEE 1547-2018 as amended by IEEE 1547a-2020, Clause 8.1.1: "For an unintentional island in which the DER energizes a portion of the Area EPS through the PCC, the DER shall detect the island, cease to energize the Area EPS, and trip within 2 s of the formation of an island."

The same document adds that no other requirement in it "shall be construed as an amendment, alteration or rescindment of this requirement". Source: Default IEEE 1547-2018 Setting Requirements, Massachusetts Technical Standards Review Group, dated Dec. 13, 2022, read August 19, 2026.

Unpacked into plain terms: DER is your solar system, the area EPS is the utility grid, and the PCC is where your house meets it. An unintentional island is a piece of the grid that has been cut off from the utility but is still being energised by something, and the standard says your inverter must notice and stop within two seconds.

The reason is a person, not an economics argument. A utility crew works on a line they have de-energised and grounded. A rooftop array pushing power back onto that line, through a distribution transformer that steps the voltage back up, makes the line lethal without warning. The rule exists so that a de-energised line stays de-energised.

Where UL 1741 fits

The equipment side is UL 1741, titled Inverters, Converters, Controllers and Interconnection System Equipment for Use With Distributed Energy Resources, Edition 3, published September 28, 2021, most recently revised August 14, 2026. Its scope states that "For interactive equipment, these requirements are intended to supplement and be used in conjunction with the Standard for Interconnecting Distributed Resources With Electric Power Systems, IEEE 1547, and the Standard for Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems, IEEE 1547.1." Source: UL 1741 product page, UL Standards & Engagement, read August 19, 2026.

So IEEE 1547 sets the behaviour, IEEE 1547.1 sets the test procedures, and UL 1741 is the listing your equipment carries to show it was evaluated against them. The Massachusetts document treats the specific supplement as sufficient evidence in several clauses: "The UL 1741 SB certification shall be considered sufficient for individual inverter based DER devices meeting ride through requirements for this function."

That is why UL 1741 appears in the compliance block of every grid-interactive product we track. The Tesla Powerwall 3 lists UL 1741 alongside UL 1741 PCS, SA, SB and Multimode. FranklinWH lists UL 1741, UL1741 SB, UL 1741 PCS, UL 1741 CRD and UL 1741 Multimode. Savant, Generac, LG, sonnen and SunPower all name it. The plain-English version of the fire and system standards that sit alongside it is in our UL 9540 and NFPA 855 guide.

What changes the answer: an islanding device

Nothing about the standard says your house cannot have power. It says your house cannot back-feed the utility. So the fix is a box that physically opens the connection to the grid, after which whatever happens inside your walls is a separate small grid that the utility is no longer part of. That box is the islanding device, and it is what a battery system actually buys you.

Once the connection is open, the battery's inverter forms a stable voltage and frequency inside the house, and the solar inverter can synchronise to that and start producing again. The array is now feeding a microgrid rather than the utility, which is exactly what the standard permits.

Every AC system in our set names the box that does it:

• Tesla publishes a specification row reading "Supported Islanding Devices: Gateway 3, Backup Switch, Backup Gateway 2" on the Powerwall 3 datasheet, and both Gateway 3 and Backup Gateway 2 carry a line reading "Backup Transition: Automatic disconnect for seamless backup".
• Enphase puts the microgrid interconnect device function in the IQ System Controller rather than in the IQ Battery 5P or 10C.
• Generac uses the Smart Disconnect Switch, which its spec guide describes as aggregating "AC-coupled PV, battery backup and generator integration" and supporting "both partial and whole home backup".
• FranklinWH uses the aGate, Anker the Backup Controller 200-H, and Panasonic the SmartBox, whose spec table includes a line for "Manual Control Over Micro-grid Interconnection".
• sonnen describes the limits of the island it forms directly, noting in a footnote that in off-grid mode, exceeding the stated current limits accounting for load "will cause the microgrid to fail".

Two consequences follow that people are not usually told at the point of sale.

There is a gap at the changeover. The islanding device has to detect the outage and open before the battery energises the house. Five of the 17 models we track publish how long that takes, from under 16 milliseconds to about 100 milliseconds, and twelve publish nothing. The table and its caveats are in our transfer times guide.

The island covers what was wired into it. A backed-up subpanel powers the circuits on it and nothing else, whatever the array is producing. Deciding which those are is the whole-home versus essential backup question, and the practical version of the whole arrangement is in our backup guide.

The narrow exception: a daylight outlet

There is one class of product that gives you something from the array during an outage with no battery at all, and it is worth knowing about mostly so you can size your expectations correctly.

SMA calls its version Secure Power Supply: a single outlet, fed from the PV array, energised by a switch during a grid outage while the inverter runs in an off-grid mode. It is a real feature and SMA is unusually direct about its limits. Its own installation manual carries a warning block stating that "Secure power supply operation must not be used for loads that require a stable electricity supply. The power available during secure power supply operation depends on the solar irradiation on the PV system. Therefore, power output can fluctuate considerably depending on the weather or may not be available at all." Source: SMA Sunny Boy Storage installation manual, Connecting the switch and outlet for secure power supply operation, read August 19, 2026.

Read that as written. It works when the sun is on the roof and not at night. Its output tracks a cloud passing overhead. It is one outlet rather than a panel. It is not automatic, because the switch is thrown by a person. It is a way to charge phones and run a fan on a sunny afternoon, and it is not what anyone means by backup power.

Why the solar does not come straight back on

The second surprise arrives when the grid returns and the array stays asleep for several minutes.

That is also the standard. Under IEEE 1547-2018 Clause 4.10, a resource does not return to service until it has confirmed the utility is genuinely healthy. The Massachusetts document publishes the required default: the resource "shall not connect or return to service following a trip (including any ground fault current sources) until detecting 5 minutes of healthy utility voltage and frequency", with a default enter service delay of 300 seconds and a 300 second ramp in steps no greater than 20 percent of the resource rating.

So a two second blip on the utility line can cost you five to ten minutes of solar production, and there is nothing wrong with the system. It is confirming that the grid is really back before it commits to it.

What this means before you buy

If backup during outages is the reason you are considering solar, the panels are not the part that delivers it. A grid-tied array with no storage produces nothing in an outage, by design, in every US jurisdiction that has adopted IEEE 1547, and no installer can configure around that.

What delivers it is the islanding device and the battery behind it, and the specifications that decide how good the result is are usable capacity, continuous power, and which circuits are inside the island. If you already have solar, the retrofit paths and their constraints are in adding a battery to existing solar. If the choice is still open between storage and a generator, that comparison is in battery vs generator.

Every requirement above is quoted from a published standard or a government document that quotes it, and every product statement is a manufacturer datasheet claim recorded against its source. Standards are adopted jurisdiction by jurisdiction and revised on their own schedule, so confirm what your utility has adopted before it affects a purchase.