DNO Application for Solar Panels

When a solar installer visits your home and starts talking about grid connection paperwork, you may hear the abbreviation “DNO application” for the first time. It sounds bureaucratic, but the concept is straightforward: before your solar panels can legally export electricity to the national grid, a formal process must notify or seek approval from the company that owns your local electricity network. This article explains what that process involves, which standard applies to your system, and why it matters for your Smart Export Guarantee payments, home insurance and future property sale.

What is a Distribution Network Operator (DNO)?

A Distribution Network Operator is the licensed company responsible for the cables, transformers and substations that deliver electricity from the transmission grid to homes and businesses in your area. Your DNO is not the same as your energy supplier — your supplier bills you for energy; your DNO owns and maintains the physical wires. Great Britain is divided into 14 distribution regions managed by six main groups:

UK Power Networks — South East England, East of England, London.
National Grid Electricity Distribution (formerly Western Power Distribution) — Midlands, South West England, Wales.
Northern Powergrid — North East England, Yorkshire.
Electricity North West — North West England.
Scottish and Southern Electricity Networks (SSEN) — South of England, North of Scotland.
SP Energy Networks (ScottishPower) — Central and Southern Scotland, Merseyside and Cheshire.

You can identify your DNO using the Energy Networks Association’s free postcode lookup at energynetworks.org. Your installer will already know which company to contact for your address.

G98 vs G99: which applies to your system?

The key threshold is 3.68 kW on a single-phase supply (16 A per phase), or 11.04 kW on a three-phase supply. Two Engineering Recommendations published by the Energy Networks Association determine which process applies:

G98 — notify after installation (small systems)

G98 (Engineering Recommendation ER G98, Issue 2 — March 2025) applies to systems at or below 3.68 kW single-phase or 11.04 kW three-phase. It uses a “fit and inform” approach: the installer commissions the system first, then notifies the DNO within 28 days. Because G98-compliant equipment has already been fully type-tested, the DNO cannot refuse the notification — they simply log the generator on their network records. The process is free of charge.

A typical 4–6 panel system with a 3.6 kWp inverter falls right at this threshold. If your inverter is rated at exactly 3.68 kW or below, G98 applies. If it is rated slightly above (say, 3.8 kW or 5 kW), G99 applies instead.

G99 — apply before installation (larger systems)

G99 (Engineering Recommendation ER G99, Issue 2 — March 2025) applies to any single-phase system whose inverter output exceeds 3.68 kW, and to most combined solar-plus-battery systems where total export capacity exceeds the G98 limit. Unlike G98, G99 requires the installer to submit a formal application to the DNO and receive approval before any installation work begins.

Standard G99 applications take up to 45 business days (approximately 9 calendar weeks) for the DNO to issue a formal Connection Offer. Many DNOs turn around smaller residential G99 cases in 4–8 weeks, and a fast-track route (sometimes called the SGI route) is available for qualifying lower-complexity systems, which can reduce the wait to around 2 weeks. The application itself is typically free; costs arise only if the DNO determines that local grid reinforcement is needed, which is uncommon for standard domestic systems but can run to hundreds or — in rare cases — thousands of pounds.

If you are adding a battery to your solar installation, ask your installer whether the combined inverter output pushes you into G99 territory — it frequently does, even when the solar-only system was within the G98 limit.

What does the DNO application process involve?

In almost every residential case, your MCS-certified installer manages the entire DNO process as part of standard commissioning. You do not need to log in to any portal or complete any paperwork yourself. What happens behind the scenes differs slightly depending on which standard applies:

G98: Installer connects the system, then submits a notification form to the DNO portal within 28 days of commissioning. The notification includes the property address, inverter make/model, rated output, a single-line electrical diagram, and confirmation of type-testing compliance. The DNO acknowledges receipt (typically within 5–20 working days) and adds the unit to their network register. There is nothing to wait for before exporting.
G99: Installer submits the application — including full technical drawings and system specification — to the DNO before installation begins. The DNO reviews the application, may run a local network capacity study, and issues a Connection Offer (approval) or a conditional offer requiring modifications. Once the homeowner accepts the offer and pays any connection charges, the installer can proceed. The system cannot legally export until the G99 approval is in hand.

Reputable installers who use specialist solar design software often generate the G98 or G99 documentation automatically as part of the design workflow, which reduces errors and speeds up submission.

What happens if a G99 application is rejected?

Outright rejections are relatively uncommon for well-designed domestic systems, but they can occur when the local distribution network has insufficient spare capacity to accept additional generation at your connection point. If the DNO rejects or conditions a G99 application, your installer can pursue one of several remedies:

Resize the system. Reducing the inverter to 3.68 kW or below moves the installation back under G98, removing the need for G99 approval entirely. The solar array can still be larger — a 5 kWp array with a 3.68 kW inverter is a common compromise.
Apply export limitation (G100). A G100 export-limiter device restricts the power your system pushes to the grid to an agreed level — for example, capping export at 3.68 kW even if the inverter is rated higher. This satisfies the DNO while preserving the benefit of higher self-consumption from a larger system.
Accept Active Network Management (ANM) terms. Some DNOs offer ANM agreements that allow connection subject to the DNO being able to remotely curtail your output during rare peak congestion periods. Curtailment is typically under 5% of annual generation in areas where ANM is offered.
Fund grid reinforcement. In the least common scenario, the DNO may offer connection subject to you funding upgrades to the local substation or cables. This route is more commonly encountered in rural areas with constrained networks.
Reapply at a later date. Grid capacity upgrades are ongoing; a rejected application today may be approvable after the DNO’s own network investment programme.

What should you do as a homeowner?

Your main job is to ask the right questions and keep the paperwork. Specifically:

Ask your installer before they start work whether your system requires G98 notification or a G99 application, and confirm they will handle it as part of the contract.
Once the installation is complete, ask for written confirmation that the G98 or G99 submission has been made, and request a copy of the DNO acknowledgement letter or reference number when it arrives.
Keep the DNO document with your MCS certificate. You will need both when applying for Smart Export Guarantee payments, when your home insurer asks about the installation, and when you sell the property — a buyer’s solicitor will request both documents during conveyancing.

If your installer never mentions the DNO — take note

An installer who says nothing about G98 or G99 notification is a warning sign. All grid-connected solar systems in the UK require one or the other — there is no exemption. Skipping the process is not a minor omission: it leaves the system operating outside the terms of its grid connection agreement, can invalidate home insurance cover, blocks SEG payments, and creates a legal problem when you sell your home.

When choosing a solar installer, check that they are MCS-certified (the certification body that underpins both the Boiler Upgrade Scheme and Smart Export Guarantee eligibility) and that their quote explicitly references DNO notification or application as part of the scope of work. If an installer quotes a price that seems unusually low and never mentions the grid connection process, the paperwork may simply not be included — or they may not be a legitimate MCS operator at all.

For a broader checklist of what separates a reliable installer from a poor one, see our guide on how to choose a solar installer in the UK.

Quick reference: G98 vs G99

	G98	G99
Inverter threshold	Up to 3.68 kW (single-phase) / 11.04 kW (three-phase)	Above 3.68 kW (single-phase) / 11.04 kW (three-phase)
Process type	Notification after installation	Application before installation
Approval needed?	No — DNO cannot refuse	Yes — DNO issues Connection Offer
Timeline	Submit within 28 days; DNO acknowledges in 5–20 working days	Up to 45 business days (standard); ~2 weeks (fast-track where available)
Cost	Free	Free to apply; grid reinforcement costs possible but uncommon
Who submits	Your MCS-certified installer	Your MCS-certified installer

Expanding an existing system above the G98 threshold is one of the most common reasons homeowners encounter G99 for the first time. Our guide to adding more solar panels to an existing system explains how the DNO process changes when you upgrade capacity.

The DNO notification is just one part of the compliance picture. Your MCS-certified installer will also handle building regulations for solar panels — including Part P electrical certification and the structural Part A checks — submitting these through their Competent Person Scheme registration so you receive the full documentation pack at completion.