Why Solar Shuts Off in a Blackout

It's the most common disappointment in residential solar: the power goes out on a sunny day and the panels do nothing. That behaviour is deliberate, required, and protecting someone.

Why grid-tied solar stops in an outage

The shutdown is anti-islanding protection, and it is required. Without it, an array would keep energising the utility line during an outage, endangering the lineworkers repairing it. Adding a battery with proper islanding capability is what changes the answer.

The reason: anti-islanding

Your solar system connects to the same wires that run to the utility's distribution network.

If the grid goes down — a fault, a storm, or crews working on the line — and your inverter kept producing, it could energize those lines from your end. A crew treating a de-energized line as safe could encounter live conductors.

That condition is called an island: a section of grid still energized by a local generator after the utility supply has failed.

Anti-islanding protection detects the grid's absence and disconnects within a fraction of a second. It's required by the standards that grid-tied inverters are certified to, and it's part of your interconnection agreement.

It's the same principle behind backfeeding dangers with generators — a local source must never energize the utility side without isolation.

Why isn't a battery alone enough?

A common misconception: add a battery and solar works in outages.

Not automatically. What makes outage operation safe is isolation from the grid — transfer equipment that physically separates your home's wiring from the utility before the system energizes it.

With that isolation in place, the system can island intentionally: your home becomes a small, self-contained grid, safely disconnected. The inverter can then produce, because there's no path to the utility lines.

Without transfer equipment, a battery is a storage device that also shuts down when the grid does.

See how home batteries work and home battery installation requirements.

The three ways to get power in an outage

1. Battery plus transfer equipment. The full solution. The system isolates, the battery supplies your loads, and — crucially — many configurations can keep the solar running while islanded, recharging the battery each day.

That last capability is the difference between a battery that lasts one evening and one that lasts as long as the sun keeps shining. Confirm your system supports it. See solar plus battery backup design.

2. An inverter with a backup outlet. Some string inverters provide a single dedicated receptacle that works during daylight outages, supplying limited power directly from the array.

Useful and cheap, with real limits: modest power, daylight only, no storage, and output varies with cloud cover. Good for charging phones and running a laptop or a small appliance — not for running a house.

3. Off-grid or hybrid configuration. Designed from the start to operate independently. See grid-tied vs off-grid solar.

What "islanding" looks like when it works

With a properly designed backup system:

1. The grid fails
2. The system detects it and opens the transfer equipment, isolating your home
3. The battery begins supplying the backed-up circuits
4. If supported, the solar restarts and contributes, charging the battery during daylight
5. When the grid returns, the system re-synchronizes and reconnects

The transition is usually fast enough that most equipment doesn't notice, though there's typically a brief interruption. Ask about transfer time if you have equipment sensitive to it.

What gets backed up

Almost never everything. Most systems energize a critical loads panel — a subpanel containing selected circuits — because whole-home backup requires much more capacity and power output.

See critical loads panel explained and essential loads vs whole-home battery backup.

An alternative is a smart panel that backs up the whole panel while automatically shedding large loads. See smart electrical panels explained.

Ask before you buy

If outage resilience is part of why you're installing solar, these questions matter more than panel brand:

1. Will this system produce during an outage? For a standard grid-tied system with no battery, the answer is no.
2. Is transfer equipment included?
3. Can solar keep running while islanded to recharge the battery?
4. Which circuits are backed up?
5. What's the transfer time?
6. What power output is available during an outage — can it start the well pump?
7. Is there a backup outlet on the inverter as a minimal fallback?

Question 3 is the one that most changes real-world outage performance, and it's the one least often asked.

If you already have grid-tied solar

You can usually add storage and backup capability later, most commonly by AC coupling a battery with its own inverter alongside your existing solar inverter — no need to replace what you have.

See AC-coupled vs DC-coupled batteries and hybrid inverters explained.

Alternatives to consider alongside: a generator (how to size a home generator) or an EV with vehicle-to-home capability (using an EV as home backup power).

The bottom line

Grid-tied solar shuts down in an outage because anti-islanding protection stops it energizing utility lines that crews may be working on — a safety requirement, not a fault. Getting power from solar during an outage requires transfer equipment that isolates your home so the system can island safely, usually paired with a battery. A battery alone doesn't do it, and the question worth asking is whether solar can keep running while islanded, because that's what turns one evening of backup into many days.

Size storage with the home battery sizing calculator, estimate production with the solar output calculator, or read solar plus battery backup design.

Standards and code reference

The standards behind this guide, for looking up in the edition your jurisdiction has adopted:

• IEEE 1547 — anti-islanding requirements
• UL 1741 — inverter safety standard, including anti-islanding

Code editions and local amendments vary. Confirm the adopted edition with your AHJ, and treat manufacturer instructions as governing wherever they are more restrictive.