Which DNO form do I need for a 4kW solar system?

A 4kW solar system on a single-phase supply exceeds the 3.68kW G98 threshold, so you need a G99 application. This applies even if your inverter is limited to less than 3.68kW export - the DNO looks at the total installed generation capacity, not the inverter export limit. Submit your G99 early as it can take 4-6 weeks for approval.

Can I install solar panels without telling the DNO?

No. Connecting any grid-tied generation without a G98 or G99 is a breach of your connection agreement and technically illegal. Your DNO will eventually detect the export via your smart meter, which records net export in half-hourly readings. Non-compliance can result in disconnection or enforcement action.

How long does G98 notification take?

G98 is a notification, not an application for permission. You submit it within 28 days of installation. Processing varies by DNO but most accept it online in minutes and you get an acknowledgment within a few working days. Your DNO has up to 10 working days to object, but in practice objections for standard domestic solar are very rare.

How long does G99 approval take?

G99 applications typically take 4 to 6 weeks for standard domestic systems. Larger or more complex installations may take 12 weeks or more and could require a network study. Your DNO has statutory timescales: 65 working days for G99 Fast-Track (up to 11.04kW single-phase or 22.08kW three-phase) and longer for full applications.

Does G98 cost anything?

G98 notifications are free. You submit them directly to your DNO via their online portal. Some third-party services charge a fee to submit on your behalf, but there is no reason to pay - the DNO portal is straightforward and takes about 10 minutes.

What happens if my G99 application is rejected?

If your G99 is rejected, the DNO will explain why. Common reasons: your local network is at capacity, your system causes voltage rise beyond permitted limits, or protection settings are incorrect. Solutions include: capping export to zero, installing an export power limiter, or connecting on a different phase. Work with your electrician or inverter manufacturer to address the specific objection and reapply.

Do I need an electrician to submit G98 or G99?

No. Anyone can submit a G98 or G99 online directly to their DNO. However, the final electrical connection must be signed off by a Part P qualified electrician for the installation to meet Building Regulations. Many electricians will handle the DNO notification as part of their service.

G98 vs G99 Explained: Grid Connection for DIY Solar in the UK

If you are installing solar panels yourself in the UK, G98 and G99 are the two forms that tell your Distribution Network Operator what you have done. One is a notification you submit after connecting. The other is a formal application you must make before you start. Pick the wrong one and your installation is non-compliant, your smart meter flags the export, and the DNO will come asking questions. Here is what each form means, which one you need, and exactly how to submit it.

Published July 2026

G98 Limit Up to 3.68kW (16A/phase)

G99 Limit Above 3.68kW

G98 Timing Notify within 28 days

G99 Timing Approve before connecting

G98 Cost Free

G99 Typical 4-6 weeks

What Are G98 and G99?

G98 and G99 are Engineering Recommendations published by the Energy Networks Association. They set out the technical requirements for connecting generation equipment to the UK's distribution network. In plain English, they are the forms you fill in to tell your DNO (or ask their permission) that you have connected solar panels, a battery inverter, or any other generator to your home's electrical supply.

Every property in the UK is connected to a Distribution Network Operator. There are six of them covering different regions: UK Power Networks (London, South East, East), National Grid Electricity Distribution (Midlands, South West, Wales), SSEN (South and North Scotland), SP Energy Networks (Central and Southern Scotland), Northern Powergrid (Yorkshire, North East), and Electricity North West. Your DNO depends on where you live, and each runs its own online portal for G98 and G99 submissions.

The key thing to understand is that G98 is a notification and G99 is an application. That is not a cosmetic difference. G98 means you can install, connect, and then tell the DNO what you have done. G99 means you need their permission before you can legally connect. Get this backwards and your inverter stays off until the paperwork catches up.

Bottom line

If your solar system is 3.68kW or less on a single-phase supply, you probably need G98. Above that, or if you have three-phase and the total generation exceeds 16A per phase, you need G99. Most DIY solar installations fall under G98 because a typical 3.5kW to 4kW system is right on the boundary - check your inverter's maximum AC output rating, not the panel wattage, to be certain.

G98 vs G99: Side by Side

Feature	G98	G99
Max system size (single-phase)	Up to 3.68kW (16A)	3.68kW to 50kW (or more)
Max system size (three-phase)	Up to 11.04kW (16A per phase)	Above 11.04kW (up to 50kW Fast-Track)
Type	Notification (install then inform)	Application (approve before install)
Timeline	Submit within 28 days of connection. DNO has 10 days to object.	4-6 weeks typical. 65 working days for Fast-Track. Longer for full G99.
Cost	Free	Free for standard applications. Complex studies may incur DNO charges.
Complexity	Simple online form. 10 minutes.	Requires inverter datasheet, single-line diagram, protection settings schedule.
Can be refused?	No (cannot refuse a notification)	Yes (network capacity, voltage rise, protection issues)
Typical for	Standard 3-4kW domestic solar, plug-in solar, small battery systems	Large domestic arrays, whole-house batteries with backup, commercial, community solar

Which One Do You Need?

The threshold is based on your inverter's maximum AC output current, not your panel wattage. A 4kW array with a 3.6kW inverter is still a 3.6kW system as far as the DNO is concerned, which keeps you on G98. A 4kW array with a 5kW inverter pushes you into G99 territory. Check the spec sheet of your inverter before you decide.

        G98 applies if: Your inverter's maximum AC output is 16A or less per phase (3.68kW on single-phase, 11.04kW on three-phase). You submit the form within 28 days of connection. The DNO cannot say no, but they can set conditions on export if your local network is weak.
      

        G99 applies if: Your inverter's maximum AC output exceeds 16A per phase. You must submit the application and receive approval before you connect. The DNO can refuse if the local network lacks capacity, your proposed system causes excessive voltage rise, or your protection settings do not meet their requirements.
      

Does 3.68kW mean the panel rating or inverter output?

The 3.68kW threshold is based on the inverter's rated AC output. The DNO does not care what your panels say on the label. A 5.2kW array with a 3.68kW hybrid inverter still comes under G98 because the inverter limits what hits the grid. This is a common point of confusion, and several inverter manufacturers (Solis, Growatt, Victron) make models specifically designed to sit right at the 3.68kW limit so you can maximise generation without triggering the G99 process.

Three-phase properties

If you have a three-phase supply, the G98 threshold is up to 16A per phase (11.04kW total balanced). But each phase must not exceed 16A individually. You also need to ensure your generation is balanced across the phases. Most domestic three-phase solar installations use three-phase hybrid inverters (like the Solis S6 or Victron MultiPlus-II) that handle this automatically.

How to Submit G98 or G99

Both forms are submitted online through your DNO's website. The process is more straightforward than most people expect. Here is the step-by-step for both routes.

G98 process

Install and connect your system -- wire everything up with your Part P electrician's sign-off.
Find your DNO at energynetworks.org -- enter your postcode.
Submit the G98 form through the DNO's online portal. You will need: your address, the inverter make and model, the inverter's rated AC output (kW), confirmation the inverter holds a valid G98/G99 type-test certificate, and the completion date.
Keep the acknowledgment -- the DNO should email you a reference number within a few working days.
Wait 10 working days -- the DNO has this window to raise any objections. For standard domestic solar, objections are extremely rare.

That is it. You are compliant. Many people worry about the G98 process because it sounds official, but it is genuinely a 10-minute form-filling exercise.

G99 process

Submit before you connect -- ideally 6-8 weeks before your planned commission date.
Gather the paperwork -- you will need: inverter datasheet showing rated AC output and THD, a single-line diagram of the installation (your electrician can draw this), the inverter's G98/G99 type-test certificate, protection settings schedule (over/under voltage, over/under frequency, rate of change of frequency), earthing arrangement details.
Submit online via your DNO's portal. Most have a "G99 Fast-Track" option for systems up to 11.04kW single-phase or 22.08kW three-phase which has a 65-working-day statutory determination period.
Wait for the offer -- the DNO will either approve, approve with conditions, or refuse with reasons. An approval with conditions might include an export power cap or a requirement for Power Frequency (G59) protection.
Connect within the validity period -- approvals are typically valid for 12 months. If you do not commission within that window, you reapply.

Common G99 gotcha: Some DNOs require a detailed network study for seemingly small systems if your local substation is near capacity. This is more common in rural areas served by long overhead lines. If you get a refusal citing network capacity, ask about an export power limiter (sometimes called an "export constraint"). Setting export to zero or a low cap often unlocks approval for the installation itself, and you can export what the network can take.

Common Myths About G98 and G99

There is a lot of bad advice floating around forums about DNO notifications. Here are the myths that keep coming up and the truth behind them.

Myth: "My electrician handles the DNO notification so I do not need to worry about it" Partly true. A good electrician will submit G98 or G99 as part of their service. But the legal requirement sits with the owner of the installation, not the installer. If the electrician forgets or gets the form wrong, the DNO will come to you. Always ask for a copy of the acknowledgment.

Myth: "G98 is optional for small systems" No. G98 is a legal requirement for any grid-connected generation under 3.68kW. Your smart meter records half-hourly net export readings, so the DNO can and does detect unmetered generation. Several installers on Reddit have reported retrospective DNO letters asking about systems that were installed years ago.

Myth: "G99 always costs money" The application itself is free for standard domestic systems. DNO charges only apply if your application requires a network study, which is unusual for systems under 50kW. If a third party offers to handle your G99 for a fee, you are paying for their time, not the DNO's charge.

Myth: "A battery-only system does not need G98 since it does not export" Incorrect. A battery inverter that can export is technically a generator and needs G98 or G99 even if you set it to zero export. The DNO does not trust that the setting will stay in place forever. Any inverter with export capability requires notification regardless of your planned operating mode.

Frequently Asked Questions

What is the difference between G98 and G99?

G98 is a notification you submit within 28 days of connecting a system up to 3.68kW (16A per phase). Your DNO cannot refuse it. G99 is a formal application for larger systems that must be approved before you connect. It typically takes 4-6 weeks and can be refused if your local network lacks capacity.

Which form do I need for a 4kW solar system?

A 4kW solar array on a single-phase supply exceeds the 3.68kW G98 threshold, so you need G99. However, if your inverter is rated at 3.68kW output, the DNO looks at the inverter's AC output rating, not the panel wattage. A 4kW array with a 3.6kW inverter stays on G98. Check your inverter spec sheet carefully.

Can I install solar without telling the DNO?

No. Connecting generation without G98 or G99 is a breach of your connection agreement. Your smart meter records net export in half-hourly readings. The DNO can detect unregistered generation and will eventually write to you. Non-compliance risks disconnection or enforcement action.

How long does G98 take?

You submit G98 within 28 days of installation. Most DNOs acknowledge it within a few working days. They then have 10 working days to raise any objections, which are very rare for standard domestic solar. The whole process is free and takes about 10 minutes online.

How long does G99 take?

Typically 4 to 6 weeks for standard domestic systems. G99 Fast-Track (up to 11.04kW single-phase or three-phase up to 22.08kW) has a 65-working-day statutory timescale. Full G99 applications for larger systems can take 12 weeks or more and may require a network study.

What happens if my G99 is rejected?

The DNO will explain why. Common reasons: local network at capacity, voltage rise beyond limits, or incorrect protection settings. Solutions include: setting export to zero, installing an export power limiter, connecting on a different phase, or upgrading your protection relay. Work through the specific objection with your electrician and resubmit.

Does G98 apply to plug-in balcony solar?

Yes. Any grid-connected plug-in system, including the 800W balcony solar kits coming to UK retailers from August 2026, must be notified via G98. The new law (SI 2026/848) makes the kits legal to install yourself, but you still submit the G98 online form within 28 days. It is a notification, not permission, and takes 10 minutes. See our plug-in solar guide for the details.

Do I need an electrician for G98 or G99?

Anyone can submit the forms directly to their DNO. However, the electrical work itself must be signed off by a Part P qualified electrician to meet Building Regulations. Most electricians will handle the DNO submission as part of the job. Read our installation guide for the full process.

Can I submit G98 myself if my electrician does not?

Yes. You do not need any special qualifications to submit a G98. Go to your DNO's website, find the G98 form, fill in your details and the inverter specifications, and submit. Keep the email acknowledgment as proof. It is free and takes about 10 minutes.

Does 0% VAT apply to solar installations that need G99?

Yes. 0% VAT on energy-saving materials applies to all solar installations regardless of whether they use G98 or G99, until 31 March 2027. The VAT relief is on the equipment and installation, not on the DNO paperwork. See our grants and incentives guide for full details.

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