Why do my solar panels stop working when the power goes out?

Grid-tied inverters are required to shut down during a blackout so they cannot backfeed hazardous power onto lines that utility crews may be repairing. It is a safety requirement, not a defect, and it means an ordinary grid-tied array has no output during an outage.

How long does the system stay off after the grid comes back?

The inverter has to see stable grid voltage and frequency before it re-energizes, and standard settings include a default delay of about 300 seconds before it returns to service. Expect several minutes of continued outage after the lines are re-energized, plus a gradual ramp back to full output.

Anti-Islanding Shutdown During Power Outages in Flagstaff

Is This Your Problem?

Standard grid-tied inverters automatically shut down during utility blackouts to prevent backfeeding hazardous power onto lines undergoing repair. The result is that the panels on your roof go dark at exactly the moment you need power most, unless the system is paired with energy storage.

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This is the single most common misunderstanding in residential solar, and it is worth stating without hedging: if your system is a plain grid-tied photovoltaic array, it will not run your house during a power outage. Not because it is broken, and not because it needs a setting changed, but because the inverter is required to disconnect and stop exporting within seconds of losing the grid. It does that so that a line worker restoring power a mile away is never exposed to a live conductor that is supposed to be de-energized.

What Islanding Is, and Why the Inverter Fights It

An "island" is any part of the grid that is still energized while the utility's supply is disconnected. If a solar inverter kept running during an outage, it would energize the wiring between your house and the fault, and everything downstream of it, using your roof as the generator. The utility cannot see that. Crews open a line that they have isolated, treat it as dead, and work on it. The equipment in the field is designed on the assumption that no distributed generator is backfeeding a de-energized line, and grid-tied inverters are certified to preserve that assumption.

The mechanism is called anti-islanding protection, and it combines passive and active detection. The inverter continuously watches voltage and frequency. When the grid disappears, voltage collapses or frequency drifts outside the settings the inverter is programmed to accept, and it trips offline. Certification standards require detection and response to an unintentional island within a matter of seconds, and modern listed inverters also perform an active test that deliberately perturbs the output slightly and looks for the response that a large interconnected grid would give and a small island would not. When the grid is present, that perturbation vanishes into it. When the grid is gone, the inverter sees the difference and stops.

Two separate safety systems get conflated with this one, and the distinction matters when you are talking to an installer. Anti-islanding protects utility line workers and the distribution system. Rapid shutdown, required by the electrical code for photovoltaic systems, protects firefighters and first responders working on or inside the building by reducing conductor voltage close to the array when the system is shut down. A home can have both, wired correctly, and still have no power in an outage. Neither system is what gives you backup power — that is a battery or a generator, and only if the system is designed and wired to island deliberately.

What Actually Happens When the Power Goes Out

Voltage and frequency trip settings are not arbitrary; they are standardized defaults that every listed inverter implements, and they explain why the shutdown feels instantaneous. A sudden blackout drives voltage below the low-voltage threshold, and the inverter clears the fault in a fraction of a second. A sag or a brownout that stays within a tolerable band may let it ride through for a couple of seconds before it trips. A frequency excursion is treated differently again: for large deviations the inverter trips quickly, while for moderate deviations the standard allows the inverter to ride through for several minutes before clearing, which is why some outages behave slightly differently from others.

Standard Inverter Trip Settings and Clearing Times

Protective function	Default threshold	Clearing time	What it means at your house
High voltage, extreme (OV2)	1.20 per unit	0.16 s	Fast trip on a severe overvoltage event; production stops almost instantly.
High voltage (OV1)	1.10 per unit	2.0 s	The band that trips on utility voltage regulation problems and feeder switching.
Low voltage (UV1)	0.88 per unit	2.0 s	A sag deep enough to dim lights but not a full blackout trips the inverter within seconds.
Low voltage, extreme (UV2)	0.50 per unit	0.16 s	This is the blackout case. Voltage collapse is detected and cleared in a fraction of a second.
High frequency, extreme (OF2)	62.0 Hz	0.16 s	Immediate trip when generation on the grid drastically exceeds load.
High frequency (OF1)	61.2 Hz	300 s	A moderate high-frequency event allows several minutes of ride-through before the inverter drops off.
Low frequency (UF1)	58.5 Hz	300 s	Same logic in reverse: several minutes of tolerated deviation, then a trip.
Low frequency, extreme (UF2)	56.5 Hz	0.16 s	Immediate trip; usually accompanied by a loss of load on the system.
Unintentional islanding detection	Certified detection function	Within about 2 s	The requirement that makes an ordinary grid-tied array physically incapable of running your house in an outage.
Return to service after the grid is restored	Voltage and frequency back in range	About 300 s default delay, then ramp	Expect several extra minutes of darkness after the neighborhood lights come back on, then a gradual climb to full output.

How Common Grid Events Look From the Kitchen Table

Event	What the inverter does	What you notice	What to do
Full blackout	Detects collapse, clears within a fraction of a second, remains off until the grid is stable	House goes dark and stays dark; the array produces nothing for the house even in full sun	Report the outage; reset nothing. Plan storage if you want these hours covered.
Brownout or deep voltage sag	Trips if voltage falls outside the low-voltage window, typically within about 2 seconds	Lights dim, then the inverter drops out while other appliances keep running	Nothing to fix. Repeated sag events on a calm day are worth reporting to the utility.
Momentary blink or reclose	Trips, then must wait out the reconnect delay before returning to service	The lights come back immediately but the solar system lags several minutes behind	Expect the delay. It is a deliberate protective setting, not a slow reset.
Feeder switching or utility maintenance on a sunny day	May ride through moderate deviations for up to a few minutes, then trip if they persist	Production pauses without the house losing power, or drops and returns on its own	Check the event log only if the pattern repeats daily, which points at a wiring or settings issue.
Multi-day winter outage	Stays off for the duration; nothing about the array can change that	Dark house, frozen risk, and an array sitting in the sun doing nothing useful	This is the case a battery with islanding capability is designed for, sized against winter conditions.
Grid restored after an outage	Verifies stable voltage and frequency, waits out the default delay, then ramps up	Neighborhood lights return several minutes before the solar system reports normal output	No action needed; verify recovery in the monitoring app the next morning.

What It Costs the Homeowner in Flagstaff

The cost of anti-islanding is measured in outage hours, and northern Arizona produces outages that are long enough to hurt. Winter storms bring wet snow and ice onto distribution lines and, along with wind, knock limbs from the ponderosa pines that grow through town and along every feeder route. Cold-weather peak loads stress equipment that is otherwise lightly used. An outage in January, when the average low is 17.6°F and record lows have reached −30°F, is not a matter of inconvenience: it is a matter of frozen pipes, a house that cannot be heated, a well pump that cannot run, and a sump or circulation pump that cannot protect anything.

The specific cruelty of anti-islanding is that it is coupled to the weather that causes the outage. On a stormy, snow-covered day the array may be producing very little anyway. But on the bright, cold, brilliantly sunny days that often follow a winter storm — precisely when your panels would be at their most efficient — a grid-tied system still produces exactly zero for the house if the grid is down. The system is generating into a disconnected wire, and every watt is thrown away by design.

There is also a subtler cost that shows up as a bad purchase decision. Homeowners who were told "solar keeps the lights on" and then experienced a three-day outage find out that the array they bought does not do that, and the fix — a battery with backup capability, a critical loads panel, and the interconnection work to support them — is a second purchase made under pressure instead of being designed into the first one. Asking the right questions before signing is where this money is actually saved.

How to Tell What Your System Can Do in an Outage

You do not need to wait for a storm to find out. The answer is written into the equipment and the wiring, and it is usually obvious within a few minutes of inspection.

Start with the equipment. A grid-tied string inverter with no battery has no backup output, and no list of settings will give it one. A battery-based system is different, and the question then becomes how the backup output is wired. Look for a backup or critical loads panel that is separate from the main panel, a transfer device inside the inverter or in its own enclosure, and inverter documentation referring to a backup or emergency power supply output. Some battery systems support full whole-home backup through a service-rated transfer device; others are deliberately limited to a subpanel of essential circuits. Both are legitimate designs, and the difference should have been explained in writing.

Then ask the operational questions, because they are what actually determine whether an outage is tolerable. Does the system automatically island during an outage, or does it need a manual action? Can it recharge the battery from the array while the grid is down, or will the battery drain with no way to refill it until the utility comes back? What is the measured runtime for the circuits you consider essential — and what does that runtime become in winter, when the battery's own cold-weather charging limits apply? Test the plan before you need it: a scheduled outage drill is a normal request, and any professional who has designed a real backup system will not be surprised by it.

What Runs in an Outage, by System Type

System type	During an outage	Can the array recharge it while the grid is down?	Practical limit
Grid-tied array, no storage	Nothing. Inverter is off for the duration.	Not applicable — there is nothing to charge.	The whole house is dark until the utility restores service.
Array plus battery with a critical loads subpanel	Only the circuits wired into the backup subpanel, typically run automatically within a few seconds.	Yes, if the system is designed to form its own grid; solar recharge during an outage depends on that capability.	Runtime depends on which loads are backed up and how much sun the array gets; a snow-covered array extends nothing.
Array plus battery with whole-home backup	The entire service can be supported, subject to the battery's power rating and available energy.	Yes, subject to the same islanding capability and to cold-weather charging limits on the battery.	Large loads such as electric resistance heat or a well pump will drain a home battery quickly; management matters.
Generator with a transfer switch, no battery	Generator-supplied circuits run; the solar inverter stays off unless the design allows it to operate with the generator.	Generally no for a simple transfer switch installation; this needs to be engineered, not assumed.	Fuel, noise, maintenance, and a manual or automatic start sequence.

What to Do About It

If reliable power during outages matters to you, the answer is storage plus a deliberate islanding design, sized against your actual critical loads rather than against a nameplate figure. The sizing conversation needs to start with a list, not a number: furnace or boiler controls, the well or booster pump, refrigeration, a few lights and outlets, internet, and any medical equipment, each with its running and starting draw. That list, plus an honest estimate of winter solar production during a storm week, decides the battery capacity.

For a Flagstaff installation there are three winter-specific points to insist on. First, the battery has to be able to accept a charge in the cold, which rules out an unconditioned exterior location for many batteries unless they have self-heating capability. Second, the system must be designed so that the array can charge the battery while the grid is down; a battery that cannot be refilled by the sun during an outage is a countdown timer rather than a solution. Third, the design must account for the days when the array itself is buried, because a winter outage after a heavy snow is the worst realistic case you will face. A backup system that assumes a fully productive array in a snowstorm has been sized against the wrong scenario.

Our matching service connects Flagstaff homeowners with vetted local solar professionals who can evaluate an existing system's islanding capability, design a storage addition around real critical loads, and explain in plain terms what will and will not work in an outage. There is no cost and no obligation, and the conversation is worth having before the next storm rather than after it.

Frequently Asked Questions

Can I keep producing if I switch off my main breaker during an outage?

No, and the idea is dangerous. A listed grid-tied inverter detects the loss of the grid and trips itself; it is not waiting on your breaker. Attempting to energize household wiring from the array by backfeeding has been done with jury-rigged cords, and it puts a live conductor where a line worker or a family member expects a dead one, with no fault protection sized for the arrangement. This is not a workaround, it is a hazard.

Does anti-islanding shut my system down for long after the outage ends?

Expect several minutes. The inverter has to see stable voltage and frequency before it reconnects, and standard settings include a default delay on the order of 300 seconds before it returns to service, after which it ramps up gradually. That is normal behavior, not a fault, and it is the same logic that keeps the inverter from reconnecting into a flickering or unstable line.