Guides · Faisalabad, Lahore, Punjab
Inverter Grid Fault During Load-Shedding: Normal or a Problem?
Short answer
If you have an on-grid solar system, an inverter grid fault during load-shedding is normal: the inverter must stop when the grid fails, even in full sun, so it cannot feed power into lines that line staff believe are dead. A hybrid inverter will also show "grid lost", but should keep your backup loads running from the battery. It becomes a problem when the fault stays after the grid returns, appears while the grid is on, or a hybrid fails to switch to battery.
Why the inverter stops: anti-islanding
A grid-connected inverter constantly checks the grid's voltage and frequency. When the grid disappears or goes outside the allowed range, the inverter disconnects within seconds. This is called anti-islanding protection, and it exists for safety. Pakistan's DISCO net-metering procedures have long required an inverter relay that trips on grid failure, so that no solar power is injected into a dead grid. Our explainer on anti-islanding covers how it works.
So a plain on-grid system shows grid fault, grid lost or a similar message for the whole load-shedding, then checks the grid and reconnects on its own. This is not a defect and no setting changes it. For power during load-shedding you need a hybrid inverter with a battery. Our guides to whether an inverter can work without a battery and hybrid vs on-grid vs off-grid explain the options, and adding batteries to an existing system explains the upgrade path.
Grid fault during load-shedding
On-grid
Must stop when the grid goes
Hybrid
Switches to battery
Quick check: normal or not?
| What you see | Normal? | What to do |
|---|---|---|
| On-grid inverter shows grid fault while the whole area has no supply | Yes | Nothing; it will restart after the grid returns |
| Inverter waits a few minutes after the grid returns, then starts | Yes | Nothing; this is the reconnection check |
| Hybrid shows grid lost and backup loads keep running | Yes | Watch battery level |
| Grid fault continues long after the grid is back and voltage looks normal | No | Check breakers and voltage protector, then call service |
| Grid fault appears daily while the grid is on, often at midday | No | See grid voltage rise below |
| Hybrid shows grid lost and the house goes dark | No | Check battery, loads and settings below |
| Three-phase inverter shows grid fault while some lights in the house still work | Often a missing phase | Report to your DISCO and installer |
After the grid comes back: why the inverter waits
When supply returns, the inverter first checks that voltage and frequency stay within limits for a set time. International interconnection rules commonly use a delay of a few minutes; the actual time depends on your inverter's grid profile.
When the fault does not clear
If the inverter still shows grid fault well after the grid is back, check, without opening anything:
- Is the grid really back at your house? Check normal loads on grid supply.
- Has the voltage protector cut off because voltage is too low or high? See our TOMZN voltage protector guide.
- Has the inverter's AC breaker tripped? If it trips again after one reset, call service.
- Is the changeover switch in the right position? See our changeover switch guide.
- Note the exact message on the screen and in the app.
Low or unstable voltage just after load-shedding
When a feeder returns, thousands of fans, ACs and motors start together and voltage can dip or swing. The inverter may connect and disconnect a few times until it settles. Now and then, that is the grid. If it happens every time, an engineer can check the cable from the meter, the voltage at your connection and the grid settings, and you may need to report low voltage to your DISCO.
Grid fault on sunny afternoons while the grid is on
This is a different problem: often the voltage at your connection point rises too high when your system exports at midday. Our guide to grid voltage rise explains it.
Hybrid inverters: what should happen in load-shedding
A hybrid also shows grid lost, then should supply backup loads from the battery and panels. Switching speed depends on the model and mode; see hybrid inverter transfer time.
If the house goes dark instead, the common causes are:
- Battery already low. If the inverter was set to use the battery through the evening, there may be little left when load-shedding starts. Our guide to SBU, SUB and utility-first modes explains how to keep a reserve.
- Overload at switchover. Heavy loads on the backup output, such as ACs, motors or an iron, can trip the inverter the moment the grid goes. See inverter overload or beeping.
- Battery communication or battery fault. See solar battery not charging or draining too fast.
- No battery fitted, or loads not wired to the backup output. Some hybrids cannot give stable backup without a battery, and only circuits connected to the backup (load) output stay on.
Three-phase systems and a missing phase
On a three-phase supply, one phase can go while the others remain, for example when a fuse at the transformer or pole fails. A three-phase inverter needs all three phases within limits, so it shows grid fault even though some lights in the house still work. Report the missing phase to your DISCO. If this happens often, talk to your installer about how loads are split. Our guide to three-phase vs single-phase inverters explains the trade-offs.
Generators and grid faults
Generator voltage and frequency drift as loads change, so an on-grid inverter may refuse to connect and show grid fault, or connect and drop out repeatedly. If it does connect, it can push solar power back into a lightly loaded generator, which risks damaging it. Solar with a generator needs engineering, often a controller that limits solar output to what the loads absorb. Read using a home generator with a hybrid inverter and, for factories, solar plus generator hybrid systems. Solar Works Pakistan designs integrated solar, grid, generator and battery systems as one of its specialist areas.
Safety
- Do not bypass, bridge or disable the inverter's grid protection, and do not ask anyone to. It protects line staff working on supposedly dead lines.
- Do not connect a generator to the house wiring without a proper changeover arrangement.
- Do not open the inverter or the DB box. Follow the restart sequence in your manual only.
For other messages, read our inverter faults guide. If the app went offline at the same time, see solar app offline or showing zero.
How Solar Works helps
For systems we install, complaints are handled by our own engineering staff. Once a complaint is registered, we target sending service personnel within 48 hours to begin diagnosis; repair time depends on the fault and parts. Our 1-year service warranty applies under the applicable project terms; after that, service is chargeable.
If you have an on-grid system and want backup during load-shedding, our engineers can assess adding a hybrid inverter and battery during a free site survey.
Get today's price or a free site survey
Grid fault that does not clear, or want your solar to keep working in load-shedding?
- WhatsApp or call: 0336 666 4321
- Email: info@solarworks.pk
- Head office: Main Boulevard, Sargodha Rd, Block F FDA City, Faisalabad
- Lahore branch for Lahore and central Punjab
We serve customers throughout Punjab, 9:00 AM to 6:00 PM daily. Site surveys are normally free. You can also contact us online.
Frequently asked questions
Why does my solar stop working during load-shedding even in full sun?
An on-grid inverter must disconnect when the grid fails, for the safety of line staff. This is anti-islanding protection and is not a fault. To have power during load-shedding you need a hybrid inverter with a battery.
How long does the inverter take to restart after the grid comes back?
It waits and checks that the grid is stable before reconnecting. The wait depends on the inverter's grid profile and settings, and is often a few minutes. A short wait after every load-shedding is normal.
Why does my inverter show grid fault even though the electricity is back?
The voltage may be too low or unstable just after load-shedding, a voltage protector or breaker may have tripped, or one phase may be missing on a three-phase supply. If the fault lasts, note the message and call service.
Can I set my on-grid inverter to work during load-shedding?
No. Grid-connected inverters must stop when the grid fails, and disabling that protection is unsafe. Adding a hybrid inverter and battery is the proper way to get backup.
Why does my hybrid inverter show grid lost and then switch off?
Usually the battery was already low, the backup load was too heavy at switchover, or the battery lost communication with the inverter. Check the battery level and loads, then ask your installer to review the settings.
Can my on-grid inverter run with a generator?
Not reliably on its own. Generator voltage and frequency vary, so the inverter may refuse to connect or may push power back into the generator. Solar and generator together need an engineered design with suitable controls.
Sources
- MEPCO, Standard Operating Procedure for DISCO net metering (24 August 2016), anti-islanding and inverter trip requirements
- SurgePV glossary, "Anti-islanding" (IEEE 1547 disconnection and return-to-service defaults)