Solar export limits, G98 and G99: what UK solar owners need to know

Helpful video reference. This guide draws on Jordan Farley's Artisan Electrics video "ARTISAN ELECTRICS v THE GRID. WHO'S TO BLAME?", which investigates a real case where a customer's solar system was being curtailed by the DNO and neither side could agree on the cause. Jordan is a qualified UK electrician and managing director of Artisan Electrics, a Cambridge-based firm with over 375,000 YouTube subscribers. His hands-on investigation of an export limit dispute is the practical background to this guide.

1. What the export limit is and why it exists

When your solar panels generate more electricity than you are using at home, the excess flows out through your meter and onto the local distribution network. The DNO - the company that owns the cables in your street - has to manage that flow. If too many homes in one area export at once, it can push the local network voltage above safe limits, trip protection devices, and potentially damage equipment.

To prevent this, every grid-connected generation installation in the UK operates under connection conditions that specify a maximum export level. For most single-phase domestic properties, that standard limit is 3.68kW - 16A at 230V, the maximum current a standard domestic connection can handle without a detailed network assessment.

On a bright summer day, a 6kW solar array on a south-facing roof in Kent can generate well above 3.68kW. Without a battery to absorb the excess and without a way to export it, that generation above 3.68kW is lost - the inverter throttles its own output to stay within the agreed export limit.

2. G98: notify after installation

The G98 Engineering Recommendation covers microgeneration systems with a maximum export of 3.68kW or less per phase. It uses a notification process:

• Your MCS-certified installer completes the installation and commissions the inverter.
• Within 28 days of commissioning, the installer notifies the relevant DNO using the G98 notification form.
• The DNO does not need to approve the installation in advance. The notification is an after-the-fact record.
• The inverter must be set to export no more than 3.68kW per phase.

G98 covers most domestic solar installations where the inverter is sized to match or close to the panel array output. A 3.5kW inverter with 4kW of panels, for example, falls comfortably within G98 limits.

3. G99: apply before installation

The G99 Engineering Recommendation covers installations where the maximum possible export exceeds 3.68kW per phase. This applies when you have a larger inverter, multiple inverters, or a high-capacity battery that can export stored energy at higher rates.

G99 is significantly more involved:

• Your installer submits an application to the DNO before any installation work starts.
• The DNO carries out a network assessment to check whether the local infrastructure can handle the additional export.
• The DNO has up to 45 working days (about nine calendar weeks) to respond.
• The DNO may approve the application, approve it with conditions, or refuse.
• Conditions commonly include a fixed export limit below your system's maximum, or a requirement for dynamic export limiting equipment.

If you are planning a system with a large battery that can export at high rates, or a very large panel array, discuss G99 with your installer before purchase. Being told after fitting that your export must be capped is a frustrating and expensive surprise.

4. How to tell if your inverter is being throttled

Most modern inverters have a monitoring app or web portal. On a clear, sunny day - say 11am-2pm in summer - look at the real-time generation reading. If it consistently hits a ceiling and stays there (commonly 3.5kW or 3.68kW) while the sun is unobscured and your battery is full, the inverter's export limit function is active.

A useful comparison: look at your generation data from cloudy days. The output curve will rise and fall with irradiance. On a clear day, if the curve hits the ceiling and flattens rather than following the sun's arc, that flat top is the export limit in action.

Some DNOs send a remote signal to compatible inverters to reduce or stop export during periods of high local network load. If you notice unexplained drops in export on otherwise clear days, this is a possible cause. Contact your DNO and ask whether active export management is in place on your connection.

5. Dynamic export limiting: more export, same rules

A fixed export limit is blunt. Dynamic export limiting is more intelligent. A current transformer (CT) clamp fitted to the incoming supply measures your household consumption in real time. The inverter reads this and adjusts its output so that the sum of export and consumption never exceeds the agreed limit.

If you are running 2.5kW of appliances at home, the inverter can export up to 1.18kW and still stay within a 3.68kW combined limit. If you switch on the kettle and consumption jumps to 4kW, the inverter briefly pulls back its output - though in practice most of that generation now powers the kettle directly rather than exporting anyway.

Dynamic export limiting requires a compatible inverter (most modern hybrid inverters support it), the CT clamp installed correctly on the incoming tails, and software configuration by the commissioning engineer. Some DNOs now require dynamic export limiting as the condition for approving G99 applications, rather than setting a lower fixed export limit. It recovers export headroom on most days while still protecting the network.

6. What to do if you want to export more

If your current system is G98-notified and capped at 3.68kW, and you want to increase your export capacity:

• Contact your MCS-certified installer and ask them to submit a G99 application on your behalf. You cannot submit it yourself.
• Be prepared for the nine-week wait and for the DNO to impose conditions.
• If the DNO approves with a dynamic export limit condition, factor in the cost of installing the CT clamp and reconfiguring the inverter.
• If the DNO refuses, the refusal is based on network capacity and there is little recourse at present - you would need to wait for the network to be reinforced.

For many east Kent properties, particularly in rural areas where the local network is older, the DNO may already be managing export carefully across multiple solar installations. Getting approval for higher export from a property on a network that is already at capacity is not guaranteed.

When to call us

If you are seeing unexplained generation losses and want to understand whether your inverter is being throttled, or if you are planning a larger solar or battery installation and need to understand whether it needs a G99 application, Richard can help interpret the monitoring data and advise on next steps. Battery and solar electrical work in east Kent.