Export limitation explained DNO limits, G98/G99 and how your inverter enforces them
Your solar system may be physically capable of exporting 6 kW to the grid — but your inverter quietly caps it at 3.68 kW. This is export limitation: a grid condition imposed by your Distribution Network Operator. This guide explains what it is, why it exists, and exactly how your inverter enforces it using real-time CT clamp data.
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Book a diagnostic — £75 → How diagnostics workWhat is a solar export limit?
An export limit is a cap on how much electricity your solar system is allowed to send back to the grid. It exists because the local distribution grid was not designed with large amounts of distributed generation in mind — and exporting too much power can cause voltage rise issues for neighbouring properties and grid equipment.
The DNO is the company responsible for the electricity cables and transformers in your area — not your energy supplier, and not Ofgem. There are six main DNOs in Great Britain: National Grid Electricity Distribution (NGED), SP Energy Networks, Electricity North West, Northern Powergrid, UK Power Networks, and Scottish Hydro Electric Power Distribution.
When your installer applies to connect your solar panels to the grid, the DNO assesses how much export capacity is available on your local feeder. They issue an approval letter specifying your permitted maximum export.
Most domestic systems fall into one of these categories:
Zero export is more common on older rural and suburban feeders with less headroom. Newer grid reinforcement schemes and smart export limitation programmes are gradually increasing available capacity.
When generation exceeds the export limit plus household consumption, the inverter enters curtailment mode. It actively reduces the amount of power the panels are producing (by adjusting its MPPT tracking point) to prevent export exceeding the permitted level.
G98 and G99: the UK connection standards
G98 and G99 are the Engineering Recommendations that govern how small generators connect to the UK low-voltage distribution network. Your installation will fall under one of these, and the letters from your DNO reference whichever applies.
Used for small generators. No prior approval needed — the installer simply notifies the DNO within 28 days of connection.
Most domestic solar installations below 4 kW inverter size use G98. The export limit is effectively set at the inverter's rated maximum output.
Used for larger generators or constrained network areas. Requires formal DNO application and approval before connection.
G99 approval letters frequently include conditions: a specific export limit (e.g. 2 kW), reactive power control, or requirements for Smart Export Limitation equipment.
Check the paperwork your installer provided at handover. If you received a G98 notification acknowledgement, your system is G98. If you received a formal G99 approval letter with conditions, it is G99. If you are not sure, your installer is legally required to have kept records — contact them with your installation address.
How your inverter enforces the export limit
Export limitation is an active, real-time control loop inside your inverter. It is not a one-time setting — the inverter constantly adjusts to keep export below the configured cap. Here is how the loop works.
A CT clamp (current transformer) is installed on the main cable between your electricity meter and consumer unit. It measures, in real time, how much power is flowing into your property (import) and out to the grid (export). This signal is sent to the inverter continuously — typically updated every few seconds.
Without the CT clamp, the inverter has no way of knowing whether power is leaving your property or being consumed on-site. The CT clamp is essential to export limiting — the two cannot be separated.
The export limit value is programmed into the inverter during installation (in watts or kilowatts). Every few seconds, the inverter compares the live CT clamp reading to this value.
When a battery is present, the inverter must account for battery charge/discharge when calculating available export headroom. A correctly configured system will:
Misconfigured systems can apply the export limit as a total output cap, preventing the battery from operating correctly. If your battery is not charging or discharging as expected and you have an export limit set, check the inverter event log for export limit interactions.
There is always a small lag between the CT clamp reading and the inverter's response — typically 0.5–2 seconds. During this window, export can briefly exceed the limit by a small amount. This is normal and expected. However, if the inverter's control loop is over-aggressive, it may overshoot in the other direction and suppress generation far more than needed.
Over-curtailment symptoms: generation appears to plateau well below expected on sunny days; portal shows frequent small curtailment events even at low output. This is often caused by a reversed or poorly positioned CT clamp giving the inverter inaccurate readings.
Zero export mode: what it means and whether it helps to have a battery
Zero export is the strictest form of export limitation: the inverter must maintain export at exactly 0 W at all times. No power from your solar panels or battery is allowed to reach the grid.
The inverter continuously monitors the grid CT clamp and curtails generation the moment export approaches zero. Because there is always a small CT clamp response lag, the system typically targets a small buffer below zero (e.g. maintaining a slight import of 50–100 W) to prevent accidental export. This is why zero export systems occasionally appear to waste a small amount of generation — the buffer is intentional.
Yes — significantly. Without a battery, excess solar generation that exceeds house consumption is simply curtailed (wasted). With a battery, excess solar charges the battery instead of being curtailed. The inverter prioritises battery charging over curtailment, so generation that would otherwise be lost is stored and used later.
Not all zero-export systems have a DNO requirement for zero export. Some installers set the export limit to 0 W by default — either as a conservative commissioning choice or because the customer asked for it (e.g. to avoid SEG admin). If your system is zero export but you have no G99 condition requiring it, you may be able to increase the limit to match your actual G98/G99 approval.
Before changing any setting, confirm your DNO approval allows export. Check the letter, not the installer's memory. If you are unsure, see the export limit issues diagnosis guide or contact the DNO directly.
How a misconfigured CT clamp breaks export limiting
Export limiting depends entirely on accurate CT clamp data. If the CT clamp is reversed, in the wrong position, or disconnected, the export limiting system cannot work correctly — and neither can self-consumption optimisation or battery charging.
A reversed CT clamp means the inverter thinks power is flowing in the opposite direction to reality. With export limiting enabled, this causes the system to believe it is exporting when it is actually importing (and vice versa).
A reversed CT clamp must be physically flipped — it cannot be corrected in software on most inverters. See the CT clamps guide for how to confirm and report the fault.
The export-limiting CT must be on the main grid connection cable — the cable between the electricity meter and the main distribution board. If it has been installed on a sub-circuit (e.g. only the solar output cable), it measures generation rather than net export and will not enforce the limit correctly.
This is more common on retrofit installs where the installer chose a convenient cable rather than the correct measurement point. It can look like the system is working normally but the export limit is not being enforced.
A loose CT clamp connector or physically damaged clamp will produce intermittent or zero readings. Without CT data, most inverters default to a safe state: either stopping export entirely (zero export fallback) or disabling export limiting entirely depending on the brand.
Can you change your export limit?
The answer depends on where the limit came from. There are two distinct situations: a limit set by the DNO as a grid connection condition, and a limit set by the installer in the inverter settings independently of the DNO. Only the second type is easily changeable.
Specified in your G99 approval letter as a condition of connection. Cannot be changed without DNO consent.
Set in the inverter settings independently, often lower than the DNO approval actually allows.
Some DNOs offer Smart Export Limitation as an alternative to a fixed low export cap. SEL uses a direct communication link (usually a broadband connection to the inverter or gateway) to send a dynamic export limit signal from the DNO to your system. On most days the limit is unrestricted; during network stress periods the DNO can reduce export remotely and temporarily. This allows higher average export than a fixed conservative cap while protecting the network during peak periods.
SEL is more common in Scotland and Wales where rural networks have limited headroom. Not all inverter brands support it — GivEnergy and Solis have developed compatible firmware. If your DNO has offered SEL, ask your installer to confirm whether your inverter supports it.
Related guides and problem pages
How CT clamps work, why direction matters, and how to perform the kettle test.
Battery chemistry, charge/discharge cycles, and how zero-export mode interacts with storage.
Step-by-step diagnosis if your inverter is actively curtailing more than expected.
How to confirm a reversed or mispositioned CT clamp and what to do about it.
What your installer should have confirmed and handed over, including export limit paperwork.
Which connection standard applies to your system, Fast Track G99, and what to do if DNO registration is missing.
Frequently asked questions
The most common reasons are: (1) your export limit is set to 0 W — all solar must be used on-site or stored in a battery; (2) house consumption is absorbing all generation and there is nothing left to export; (3) a battery is present and is absorbing the excess solar rather than exporting it; (4) the CT clamp is reversed and the inverter is incorrectly curtailing. Check your export limit setting first, then verify the CT clamp with the kettle test, then review the portal event log for curtailment messages.
Yes, indirectly. Smart Export Guarantee payments are based on actual metered export from your property (measured by your smart meter, not the CT clamp). If your export limit means you can only export 2 kW instead of 5 kW on a sunny afternoon, you will accumulate fewer exported units and receive lower SEG payments. Systems with zero export receive no SEG payments, regardless of how much they generate. Adding battery storage and increasing self-consumption is the most practical alternative to increasing the export limit.
It depends on why the limit was set. If the G99 approval from your DNO specifies the limit, your installer is correct — you would need a formal variation from the DNO. However, if the installer set the limit lower than the DNO approval allows (or set zero export out of habit), there is no barrier to increasing it to the permitted level. Request a copy of your G99 approval letter and compare the approved export limit to what is currently programmed in the inverter. If there is a gap, the limit can be raised — the installer just needs to access the installer-level settings to make the change.
Under G98, a single-phase connection allows up to 3.68 kW export (16 A at 230 V). A three-phase G98 connection allows up to 11.04 kW (3.68 kW per phase). These are technical maximums — your DNO may impose a lower limit based on local network capacity. Systems above 3.68 kW (single-phase) or using G99 can have any export limit the DNO specifies, from zero up to the inverter's rated maximum. Check your approval letter for your specific installation.
Yes — and this is common. A 6 kW array with a 3.68 kW export limit is a typical configuration. The extra generation capacity is not wasted — it charges a battery and powers house consumption. On very sunny days when battery and load cannot absorb the full 6 kW output, the inverter curtails the panels to keep export within the permitted limit. Oversizing the array relative to the export limit increases self-consumption and battery charge times but does reduce the effective use of your panels on peak sunny days.
Export limit issue or unexpected curtailment?
If your system is curtailing more than expected, your CT clamp readings look wrong, or you are not sure what your DNO approval actually permits, a remote diagnostic session reviews your portal data and inverter settings to find the cause — usually within 30 minutes.