Guides · Faisalabad, Lahore, Punjab
Anti-Islanding: Why On-Grid Solar Shuts Off in Load-Shedding
Short answer
Anti-islanding is a safety function built into every grid-connected solar inverter: when the grid supply fails, the inverter must stop feeding power into it within a couple of seconds. That is why an on-grid system goes dark during load-shedding even on a bright afternoon. It is not a fault. It protects the linemen working on "dead" wires, and it is a condition of connecting solar to the grid. If you want power during outages, the answer is a hybrid system with a battery, which creates its own separate, safe supply for your house.
Our guide can a solar inverter work without a battery? covers what each inverter type does in an outage. This article explains the protection itself: what islanding is, how inverters detect it, and the safe ways to keep the lights on.
What "islanding" means
Picture your feeder: the 11 kV line, the pole-mounted transformer in your street and the low-voltage wires to each house. Normally the whole network is fed from the grid.
When the DISCO switches the feeder off, for load-shedding or repairs, that section is supposed to be dead. But if solar inverters on several roofs kept running, they could keep a small part of the network energised on their own. That isolated, live section is an island.
An island is dangerous for three reasons:
- Line worker safety. A lineman who has switched off a feeder expects the wires to be dead. Solar back-fed through a transformer can make them live, at high voltage on the 11 kV side.
- Damage when the grid returns. An island drifts out of step with the grid. When the feeder is switched back on, the two supplies can clash, stressing transformers, motors and the inverters themselves.
- Poor quality supply. An island has no proper control of voltage and frequency, which can harm appliances.
Anti-islanding
Grid on
Inverter exports
Grid off
Inverter stops so lines are safe
How an inverter detects that the grid has gone
An on-grid inverter does not make its own voltage reference. It follows the grid. When the grid goes, it must notice quickly, even in the hard case where the solar output happens to match the local load almost exactly, so voltage barely changes.
Inverters use two kinds of detection:
| Method | How it works | Strength |
|---|---|---|
| Passive | Watches voltage, frequency and the rate at which they change. Trips if they move outside set limits. | Simple and fast when the change is large |
| Active | Nudges its own output slightly, for example a small frequency shift, and watches the response. A live grid absorbs the nudge; an island does not. | Catches the balanced case that passive methods can miss |
Most modern inverters combine both. The international test for this, IEC 62116, checks that an inverter disconnects within 2 seconds, including under the balanced-load case.
What the DISCO requires
The DISCO net-metering reference guide we reviewed requires islanding protection to recognised standards (it cites IEC 61727, IEEE 1547 and UL 1741), sets fast trip times for voltage and frequency going out of limits, and requires the inverter to stay off for at least one minute after the grid returns to normal. DISCO staff are asked to test the anti-islanding function during the connection inspection, and the installation must have a lockable manual disconnect switch that DISCO staff can reach. For the application process itself, see our green meter and FESCO/LESCO guide and net billing guide.
What you see on the inverter
During load-shedding a grid-tied inverter typically shows a message such as "grid lost", "no grid" or a utility fault code. When the supply returns, it waits for a reconnection delay, often a minute or more, while it checks that voltage and frequency are stable, then starts again on its own. The exact delay is set in the inverter and its country settings.
If the inverter shows a grid fault while the grid is clearly on, that is a different problem. Read inverter shows grid fault during load-shedding and, for midday trips on sunny days, grid voltage rise: why your inverter trips.
How hybrid systems give backup safely
A hybrid inverter with a battery does not break the anti-islanding rule. It works differently:
- When the grid fails, an internal relay disconnects the inverter from the grid side within the required time, just as an on-grid inverter would.
- The inverter then supplies a separate backup circuit in your house from the battery and panels. That circuit is no longer connected to the DISCO network, so nothing flows back to the street.
- When the grid returns and is stable, the inverter reconnects and goes back to its normal mode.
This is an intentional, isolated island inside your home, which is safe because of the physical disconnection. How quickly the switch happens, and whether computers and routers notice it, is covered in load-shedding switchover: how fast hybrid inverters transfer. Operating modes such as SBU and SUB are explained in SBU, SUB and utility-first modes.
Which loads go on the backup circuit is a design decision. A battery sized for lights, fans and a fridge cannot carry every air conditioner in the house.
What about running solar with a generator?
An on-grid inverter needs a stable AC reference to follow. A generator can provide one, but generator frequency and voltage are less steady than the grid, and solar can push power back into a lightly loaded generator, which many sets cannot accept. Combining them safely needs a designed control arrangement, not just a cable. See using a home generator with a hybrid inverter, solar plus generator hybrid for factories and changeover switches.
Never bypass anti-islanding
Some people ask whether the protection can be switched off, or whether a changeover can be wired so an on-grid inverter keeps running during outages. Do not do it.
- It can kill a lineman working on the feeder.
- It can damage your own inverter and appliances when the grid returns out of step.
- It breaks the conditions of your grid connection and can lead the DISCO to disconnect you.
- It will usually void the inverter's manufacturer's warranty.
If you want backup, choose the right system instead. Our hybrid vs on-grid vs off-grid guide compares the options.
Choosing the right setup
| Your situation | Sensible choice |
|---|---|
| Few outages, daytime use, lowest cost | On-grid; accept no supply during load-shedding |
| Regular load-shedding at home | Hybrid inverter with a lithium battery on a backup circuit |
| Hybrid now, battery later | Hybrid inverter, with the battery type and voltage chosen at the start |
| Factory with a generator | On-grid or hybrid with an engineered generator interface |
| Factory needing outage cover without diesel | Hybrid with battery storage (BESS) |
For equipment rates, see our solar inverter price and lithium battery price pages.
How Solar Works Pakistan designs for outages
Our in-house engineers start from your outage pattern, your essential loads and whether a generator is already on site. Hybrid systems, generator integration and BESS are core parts of our work, from homes of about 6 kW up to megawatt-scale industrial plants. All necessary tests for safe commissioning, including protection settings, are completed before handover, and we show you how the system behaves in an outage. See our solar installation services.
Get today's price or a free site survey
- WhatsApp or call: 0336 666 4321
- Email: info@solarworks.pk
- Head office: Main Boulevard, Sargodha Rd, Block F FDA City, Faisalabad
- Lahore branch: 2nd Floor, Jeff Heights, Gulberg, Lahore
- Hours: 9:00 AM to 6:00 PM, daily
We serve customers throughout Punjab. See our Faisalabad and Lahore pages, or contact us.
Frequently asked questions
What is anti-islanding in a solar inverter?
It is a protection function that stops a grid-connected inverter from feeding power when the grid supply fails. It prevents solar from keeping a section of the DISCO network live while it is supposed to be off.
Why does my on-grid solar stop during load-shedding?
Because anti-islanding requires it to disconnect when the grid goes. An on-grid inverter has no battery and no separate backup circuit, so it simply stops until the grid returns.
How quickly must an inverter disconnect?
The international IEC 62116 test checks that it disconnects within 2 seconds. Trips for large voltage or frequency changes are faster still.
Can I turn off anti-islanding to get power during outages?
No. It endangers line workers, can damage equipment, breaks your connection conditions and usually voids the warranty. Use a hybrid system with a battery instead.
Does a hybrid inverter have anti-islanding?
Yes. It disconnects from the grid when the supply fails, then runs your backup circuit from the battery and panels as a separate supply that is not connected to the street.
Why does my inverter take a while to restart after the grid returns?
It waits until grid voltage and frequency have been stable for a set time before reconnecting. This delay is a normal part of the protection.
Can my on-grid inverter run with a generator?
Sometimes, but only with a properly designed control arrangement, because solar can push power back into a lightly loaded generator. Ask an engineer before connecting them.
Sources
- Clean Tech Controls, "IEC 62116 test of anti-islanding protection"
- PPIB, "Net Metering Reference Guide for DISCOs" (PDF)