What you will see
- The inverter is powered, but designated backup appliances are off.
- Backup fails when the grid goes off, or stays unavailable after electricity returns.
- The screen or app may show an overload, battery or communication warning.
Why it happens
During load-shedding, the battery may be switched off, at its discharge limit or in protection. A battery communication problem can also stop normal backup. Charge remaining on the display does not guarantee the battery can deliver the power needed.
While grid electricity is available, a tripped backup breaker or earth-leakage device, a wiring fault or a changeover problem can interrupt the supply to backup circuits. The installer may also need to check that the backup function is correctly enabled and commissioned.
In either situation, appliances must be connected to the designated backup output or an approved backup arrangement. An overloaded backup output can shut down independently of the display. Heavy appliances and motor starting currents may exceed its limits.
No battery installed? Battery-free backup must be explicitly supported for the exact inverter model, firmware and installation. Where it is supported, cloud cover or a sudden increase in load can leave too little power, and solar alone cannot provide backup after dark. Running normally with the grid on does not prove the system can back up without a battery.
Four places backup power can stop
- 1Battery switched off, at its discharge limit, in protection or not communicating with the inverter.
- 2Backup output overloaded by heavy appliances or motor starts, or the backup function not enabled.
- 3Backup breaker or earth-leakage device tripped.
- 4Appliance plugged into a socket that is not on a backup circuit.
A lit screen does not prove the backup output is on. Photograph the inverter and battery displays before calling.
What inverter backup not working means on a hybrid
A hybrid inverter has two sides on the house end. The grid port connects to your DISCO supply through the main DB. The backup port, also called EPS, load or AC output, feeds the essential circuits. When the grid fails, the inverter disconnects from the grid (anti-islanding) and keeps the backup port live from battery and solar. Our backup loads panel guide explains this split in detail.
So "backup not working" can mean the backup port never comes on, it comes on and then drops, or it works but the room you care about is on the grid side. Related problems are covered elsewhere: grid fault messages after the light returns are in inverter grid fault during load-shedding, and short blinks when switching are in hybrid inverter transfer time.
Backup not working
Mode
Backup output disabled
Battery
Empty or not detected
Overload
Backup tripped
Quick-check table: no backup during load shedding
| Symptom | Likely cause | Safe owner check | Call an engineer if... |
|---|---|---|---|
| Whole backup side dark, screen shows low battery | Battery at cut-off SOC or low-voltage limit | Note SOC on screen; was it low before the light went? | Battery was well charged and still no backup |
| Backup comes on, then drops with beeping or "overload" | Too much load at switchover (AC, motor, iron) | Note what was running; reduce load | It trips with only light loads |
| Backup worked before, stopped after a restart or update | Backup/EPS function switched off in settings | Check the app or screen for the backup or off-grid output setting | You cannot find the setting, or it switches off again |
| Inverter screen shows battery missing or BMS error | Battery off, asleep, or communication lost | Look at the battery breaker and battery LEDs | Always; do not reset repeatedly |
| Some rooms on, one room dark | That circuit is on the grid side | Check which breakers are in the backup panel | Circuit should be on backup; wiring change needed |
| Backup panel dark, inverter shows output normal | Backup panel breaker tripped | Look at the backup panel breakers | It trips again after one reset |
| Inverter shuts down completely when grid goes | On-grid inverter, or hybrid with missing backup device | Check model; on-grid inverters cannot give backup | You were sold the system as having backup |
| Backup only fails at night | Battery empty or too small for night load | Read SOC at sunset and at the moment backup stops | Battery is full and still fails |
Safety first
Safety box. The backup port stays live from the battery when the grid is off. Treat every socket and wire on the backup side as live during load-shedding. Do not open the inverter, the backup panel cover or any DC or battery wiring. If you smell burning or see smoke, switch off in the manufacturer's sequence only if you can do so safely, keep away and call a qualified engineer.
Safe owner checks, step by step
- Read the screen and app at the moment the light goes. Note the exact message (low battery, overload, battery fault, grid lost, off-grid disabled) and take a photo.
- Check the battery SOC. If the battery was already at its cut-off level, the inverter has nothing to switch to. In SBU mode, a battery used all evening can be empty before late-night load-shedding starts. See SBU, SUB and utility-first modes and inverter battery low voltage.
- Think about what was running. Two ACs, a water motor and an iron starting together can trip the inverter on overload at switchover. See inverter overload and beeping.
- Look at the backup panel breakers by eye. If one has tripped, you may reset it once. If it trips again, leave it off and call. See solar breaker tripping.
- Look at the battery. Are its LEDs on? Is its breaker or switch on? A battery that has gone to sleep after a deep discharge is covered in lithium battery not turning on.
- Check the backup setting in the app (view only). Some brands have a setting that must be on for the backup port to work during an outage.
- Check the changeover. If you have a manual changeover or generator ATS, confirm it is in the normal position. See changeover switch for solar.
- If the inverter has locked out, restart it only in the manufacturer's order. See how to restart a solar system safely.
- Send photos of the screen, the app and the backup panel to your installer, with the inverter and battery model.
EPS output not working: the setting that catches people out
On several grid-tied hybrid inverters the backup port is a function that must be enabled, not something that works automatically. GoodWe's EM series manual, for example, says the "Back-Up Supply" option must be turned on in the SolarGo app for the backup port to supply power, and that an "Off-Grid Output Switch" must be on for off-grid operation. The same manual warns that restarting the inverter or battery can switch this function off.
That is why EPS output not working after an update, battery replacement or long shutdown is common. The setting's name differs between models. Do not change other settings while you look; if you cannot find it, ask your installer.
Overload and longer restart delays
The same GoodWe manual explains that when backup overload protection repeats, the inverter waits longer and longer before trying again, up to one hour, unless the overload history is reset in the app after reducing load. Other brands behave differently, but the lesson holds: if backup fails after an overload, reduce the load first. Restarting repeatedly with the same load connected does not help. See inverter keeps restarting.
Backup devices on some three-phase hybrids
Some grid-tied hybrids need an extra device before the backup port works at all. Huawei's datasheet for the SUN2000-5-12K-MAP0, for example, lists a SmartGuard as the backup device and gives the switchover time "with SmartGuard". If that device is missing, not wired or faulty, there may be no backup when the grid fails.
Hybrid inverter not giving backup: what an engineer will check
- Backup and off-grid settings: enabled, correct output voltage and frequency, correct battery cut-off for off-grid use.
- Battery health and communication: BMS link, battery firmware, SOC calibration, and whether the battery is allowed to discharge in off-grid mode. See battery and inverter communication.
- Backup port wiring: correct terminals, cable size, neutral and earth arrangement. A backup port must never be connected to the grid side; manuals list this as an unacceptable installation.
- Backup load size against the inverter's backup rating, including motor and AC starting currents.
- Backup device or relay on models that use one.
- Transfer behaviour: the inverter correctly detecting grid loss and switching over. See anti-islanding.
- Firmware on inverter and battery.
How to prevent backup failures
- Keep a battery reserve for load-shedding hours, so backup is still there at 2 AM.
- Keep heavy loads off the backup panel unless the system was sized for them.
- Test backup after any change: firmware update, battery replacement or new wiring. Label the backup panel.
- Match the battery to your backup hours. If backup runs out early, see battery backup time reduced.
- Know your inverter type. An on-grid inverter without a battery cannot give backup; see can a solar inverter work without a battery?
How Solar Works Pakistan helps
For systems we install, our own engineering team handles after-sales complaints. WhatsApp 0336 666 4321 with a photo of the screen or app at the moment backup failed, plus the inverter and battery model. We target sending service personnel within 48 hours of a registered complaint to begin diagnosis; fix time depends on the fault, parts and any manufacturer involvement. Our 1-year service warranty applies under the applicable project terms. See how after-sales service works and our solar troubleshooting guide.
We can also check backup faults on hybrid systems installed by other companies, as a chargeable service, across Punjab.
Frequently asked questions
Why is my inverter backup not working during load-shedding?
Most often the battery is already at its cut-off level, the inverter tripped on overload at switchover, the backup function is disabled in the settings, or the circuit is on the grid side. The message on the inverter screen usually tells you which.
Why is my hybrid inverter not giving backup when the battery is full?
Check for an overload or backup-disabled message, a tripped backup panel breaker, or a battery communication error. On some models the backup function switches off after a restart and must be turned on again in the app.
What does EPS mean on an inverter?
EPS stands for emergency power supply. It is the backup output that stays live from battery and solar when the grid fails. Some brands call it backup, load or off-grid output.
Why is there no backup during load shedding at night only?
Usually the battery has been used during the evening and reaches its cut-off before the outage. Ask your installer to review the mode and reserve settings so some battery is kept for load-shedding hours.
Can an on-grid inverter give backup during load-shedding?
No. An on-grid inverter without a battery must shut down when the grid fails, for line workers' safety. You need a hybrid inverter with a battery for backup.
Should I reset my inverter if backup stops?
Reduce the load first, then restart only in the manufacturer's order, once. If backup fails again, stop and call your installer with photos of the screen.
Sources
- GoodWe, EM Series hybrid inverter user manual V1.3 (2024): "Back-Up Supply" and "Off-Grid Output Switch" settings, backup overload restart behaviour, backup side must not connect to grid: https://www.memodo.de/mwdownloads/59e32dbd477958aeb7489b392c04e665
- Huawei, SUN2000-5/6/8/10/12K-MAP0 datasheet (backup device and switchover time)
What you can check yourself
- Note whether grid power is available and whether all backup circuits or only one are affected.
- Photograph the inverter message and, if fitted, the battery display and warning lights.
- Record which appliances were running or starting when power stopped. Switch off unnecessary heavy appliances at their normal switches, if safe.
- Photograph labelled breaker positions only where you can see them without opening electrical covers.
What not to do
- Do not open the inverter, battery or electrical board, or unplug battery cables.
- Do not bypass protection, join circuits together or change battery and backup settings.
- Do not repeatedly reset a tripping breaker or restart the system to clear a recurring fault.
When to call us
- Designated backup circuits stay off, including when grid power returns.
- A breaker repeatedly trips, or battery and overload warnings return.
- If there is smoke or sparking, keep away and call emergency services first.
Hybrid backup support in Faisalabad and Lahore
Our Faisalabad and Lahore teams work on hybrid solar systems across Punjab built on Solis, GoodWe, Growatt, Huawei, Inverex and Luminey inverters with lithium batteries. Backup functions and recovery steps depend on the exact model, so we check your model’s documentation before changing anything.
Send us
The inverter model, battery model if fitted, photos of the warnings, your city and area, and the appliances in use when power stopped. Tell us whether the grid was available and whether backup has ever worked correctly.
Technical references
Reviewed 24 September 2026. Manufacturer documents are cited for general principles; your exact model’s manual always applies.