Zero-export system showing export

If you are new to export limiting, our zero export device guide explains how it works and when you need it. This page is for a system that already has it and is not behaving.

What "zero export not working" means

Zero export (also called export limiting or anti-backflow) is a feedback loop. A CT clamp or small smart meter at your grid connection measures which way power is flowing. The inverter reads that signal many times a second and cuts its output as soon as power starts to flow out to the grid.

If any part of that loop is wrong, the inverter cannot tell import from export. Three things then happen:

• The inverter keeps exporting, because it believes the house is still importing.
• Your DISCO meter records export units that you may not be entitled to without an approved net billing agreement. See our net metering and net billing guide.
• The app shows odd numbers, such as negative consumption or import and export swapped.

Normal versus not normal

Quick-check table

Safe owner checks

You can do the following from the app, the inverter screen and your appliances.

Safety. The CT clamp and meter sit on live mains cables inside the distribution board. Do not open the board, move the CT or change installer-level settings. If you see scorch marks or smell burning, switch off in the order your installer showed you, keep away and call a qualified engineer.

1. Check the time and conditions. Zero export only matters when solar is bigger than your load: usually late morning to mid-afternoon on clear days, with few appliances running.
2. Read the inverter screen and app for alarms. Look for messages about the meter, CT, smart meter or power sensor. Names vary by brand. Our inverter faults guide covers common ones.
3. Do a simple load test. At midday, with the app open, switch on a large load such as an electric kettle or iron and note the reading. Then switch it off. With a correct CT, consumption rises when you switch on and export stays at or near zero when you switch off. If the numbers move the wrong way, the CT direction or sign is probably wrong.
4. Read the DISCO meter. If your meter shows separate import and export registers, write both down at the same time on two or three days. Do not open or tamper with the meter. If the export register rises on sunny days, real export is happening. Our AMI smart meters guide explains two-way meters.
5. Check for recent changes. A firmware update, new dongle, router change, rewiring or a new appliance circuit added after a certain date are all useful clues. If the inverter's controller depends on its dongle or logger, a dongle problem can stop limiting too; see inverter Wi-Fi setup and solar app offline.
6. Take photos and screenshots. Inverter model, screen, app power-flow page at midday, and the meter display.

What an engineer will check

• CT polarity. Solis's own guidance, for example, sets up a pure import condition and expects every phase to read as import; any phase showing export has a reversed CT, fixed by turning it round on the cable. Other brands use a similar logic. Some apps, such as SolisCloud, also have a CT detection function that installers can run under set conditions.
• CT position. The CT must be on the main incoming cable, before any circuit branches off. If it sits after a branch, the inverter does not see the load on that branch.
• Phase matching on three-phase sites. Each CT must be paired with the right voltage phase. A mismatch can give wrong readings or even flip the sign.
• Meter communication. The meter type, address and communication wiring must match what the inverter expects.
• Limit mode and fail-safe. Huawei's manual, for example, offers unlimited, zero-power and limited-power modes, a choice between total power and single-phase limiting, and a fail-safe that reduces output when meter data is lost. On a meter that records each phase separately, limiting total power may not be enough.
• Multiple inverters. Where there are several inverters, they need a shared controller or logger so all of them limit together.
• Hybrid behaviour. When the battery is full, a hybrid must throttle; the engineer checks battery and export settings work together.

How to prevent zero export problems

• Ask for a load test at commissioning, with the app open, showing export held at zero.
• Keep a screenshot of the correct export settings and the inverter's firmware version.
• After any firmware update, dongle replacement or rewiring, repeat the simple load test.
• Do not let anyone add circuits ahead of the CT position in the board.
• If you later get an approved net billing agreement, have the limit changed properly rather than switched off. If credit then does not appear, see net billing credit not showing.

For Solar Works customers

Our engineers fit the sensor approved by the inverter manufacturer, set the limit during commissioning and test it under real load. If export appears on a system we installed, WhatsApp 0336 666 4321 with the inverter model, a photo of the screen and screenshots of the app's power-flow page at midday. Our 1-year service warranty applies under the applicable project terms, and after-sales complaints are handled by our own engineering staff. See how after-sales service works and the Huawei and Solis brand pages.

We can also diagnose export-limiting problems on systems installed by other companies, as a chargeable visit in Punjab.

Frequently asked questions

Why is my inverter exporting with zero export on?

Most often the CT sensor is facing the wrong way, is on the wrong cable or phase, or has lost communication with the inverter. Less often, the setting has reset after an update or is limiting total power while one phase still exports.

CT sensor wrong direction: what happens?

The inverter reads export as import. Instead of cutting back, it can push more power out, and the app may show negative consumption. An engineer fixes it by turning the CT round or correcting the setting, then repeats a load test.

Why is my export limit not working after a power cut?

The meter or CT link may not have come back properly, or the dongle that acts as the controller may be offline. Check for a communication alarm. A correctly set fail-safe should reduce output when meter data is lost.

Is a small amount of export normal with zero export?

A brief spike of a second or two when a heavy load switches off can happen while the inverter reacts. Export that builds up over an afternoon is not normal and should be checked.

Can I move the CT clamp myself?

No. It sits on live mains cables inside the distribution board. Moving or opening it must be done by a qualified electrician with the supply isolated.

Why does my app show export but my meter does not?

The app's sign or CT setting may be reversed, so it labels import as export. Compare the meter's registers over a few days. If the meter shows no export, ask your installer to correct the app setting.

Does zero export work during load-shedding?

During load-shedding there is no grid to export to. An on-grid inverter shuts down, and a hybrid supplies only its backup loads from solar and battery.

Sources

1. Solis, "Smart meter phase rotation and CT polarity verification"
2. Solis, "CT detection function on the SolisCloud app"
3. Huawei, SUN2000-(3KTL-10KTL)-M0 user manual, "Setting export limitation parameters"