Your Distribution Network Operator (DNO) registers generation under G98 or G99 so the network knows what you connected. That registration is separate from export payments. Getting paid for surplus still needs a supplier export tariff, and usually a separate export MPAN. DIYers can file G98 and G99 themselves; you do not need an MCS installer for the DNO forms.
Use G98 (connect and notify within 28 days) for single-phase systems up to 3.68 kW AC. Use G99 (apply and wait for approval before install) when AC capacity per phase is above that limit. You will need your import MPAN, inverter make and model with ENA type-test reference, total AC capacity, and a single-line diagram. Once the DNO side is done, the Octopus export route is covered in how to export DIY solar with Octopus.
G98 vs G99: which path do you take?
The decision is driven by AC generation capacity per phase, not by how many panels you can fit on the roof. On a single-phase supply the usual domestic boundary is 16 A per phase, which is 3.68 kW AC at 230 V for type-tested kit under G98.
| G98 | G99 | |
|---|---|---|
| System size (single phase) | Up to 3.68 kW AC | Over 3.68 kW AC |
| When to apply | After install, within 28 days of commissioning | Before install; wait for approval |
| Typical processing | Often about 10-15 working days after notification | Often 8-12 weeks; some DNOs longer |
| Cost | Usually free notification | Application may be free; DNO can charge for studies or works |
| Can DNO reject or constrain? | Notification route for compliant type-tested kit | Yes: approval, export limits or works can apply |
| Forms | G98 single-premises notification | G99 application (including fast-track routes where eligible) |
| DIY eligible? | Yes | Yes |
| What you get | Network record that generation is connected | Permission to connect the declared capacity / arrangement |
| What you still need for export pay | Supplier export process + usually export MPAN | Same: DNO approval is not an export tariff |
Plan the DNO route before you finalise the roof layout
Before I committed to a panel count and a roof drawing, I worked backwards from the DNO route. The thing that decides G98 versus G99 is the AC generation capacity per phase, not the number of panels you can fit on the roof. National Grid’s G98 guidance sets the single-phase boundary at 16A per phase, which is 3.68kW at 230V on type-tested kit. The wait for G99 approval is also why installer quotes tend to stop short of 4 kWp. Above that you are into G99, which has to be approved before you install.
So before I drew anything on the roof, I picked a candidate inverter and looked it up on the ENA Generator Type Test Register. That gave me the device reference number I would need on either form, and it confirmed the AC nameplate. From there, the roof layout became a sanity check rather than a guess: can the array fit, will it actually load that inverter, am I staying within G98, and if I am going G99, what export figure or export-limitation device am I declaring.
Roof orientation does not change the DNO category, but it changes the inverter you pick and how hard you push the AC limit. A south-facing roof can produce a sharper midday peak, so a strict 3.68kW AC system on a south roof may clip more than the same kit split east and west. A split layout often spreads the curve and may let a slightly larger DC array sit happily behind a G98-compliant inverter. This is design reasoning, not an official DNO rule, so model it with your own shading and tilt before you commit.
Flat roofs are a separate planning job. Row spacing, ballast, edge zones and a safe walking route around the array all eat usable space, so the panel count you can register is whatever survives the layout, not the maximum the roof area suggests. Get the roof drawing finished first, then take the resulting array DC and AC numbers to the DNO form. See mounting equipment for the practical side of fixings and rails.
Scaffolding timing is not a DNO rule, but it is the rebook you do not want. Before the boards go up, lock the full scope: panels and layout, cable route, isolator and inverter location, bird protection, and any provision for a future battery or hybrid inverter. If a G99 decision lands after the scaffold comes down, that can mean a second access visit and a redesign you were not planning for.
Battery-ready design feeds straight back into the form. If you might add storage later, picking a hybrid inverter up front, or planning how an AC-coupled battery will sit behind your meter, affects both export capacity and whether you need a separate export limitation device. The G99 form asks for the device reference number of any external export limitation kit, so it is worth deciding that early rather than retrofitting and re-notifying.
Determine your system size and DNO application type
The type of application depends on your solar system’s AC capacity:
- G98 application: smaller systems up to 3.68 kW per phase (16A). The DNO uses a “connect and notify” approach: install first, inform the DNO afterwards, within 28 days of commissioning.
- G99 application: if capacity exceeds 3.68 kW per phase, apply under G99. Approval is required before installation. The G99 process is more detailed and may take 8-12 weeks.
Three-phase supplies raise the G98 ceiling to 3.68 kW per phase. Most homes are single phase, so check the supply before planning around 11.04 kW. See the three-phase solar UK guide.
Plug-in solar panels are a separate policy track. Until the socket rules are enabled, treat any generation connected to your wiring as a normal G98/G99 question for hardwired systems, not a shortcut around DNO registration.
What to keep: documents checklist
Store these together before, during and after the DNO process. Suppliers, future buyers and any later upgrade will ask for them.
- Import MPAN from your electricity bill (or National Grid MPAN lookup)
- Inverter make, model and AC rating, plus the ENA type-test / device reference number
- Single-line diagram showing panels, inverter, isolators, consumer unit and meter
- Submitted G98 or G99 form and any portal reference number
- DNO response letter (G98 acceptance or G99 approval / constraints)
- Electrical Installation Certificate (EIC) for notifiable connection work
- Building Regulations compliance certificate where the electrical work was notifiable
- Export limitation device details if you declared one on a G99 form
- Photos of nameplates and isolators for later export or insurance questions
Gather the necessary information for the DNO
Before filling out your application, gather these essential details:
- System specifications: technical information about your solar panels, inverters, and overall system capacity. The crucial piece is the inverter make and model number. Look it up on the ENA type test register. Not sure which inverter to choose? Our guide covers the key specs to check.
- Schematic diagram: a simple layout showing how your system connects to your property’s electrical infrastructure, including the location of the inverter and isolator switches.
- MPAN number: the unique number that identifies your electricity meter. It is often on your electricity bill. You can also look it up by address on the National Grid site.
Which DNO covers your area?
Your DNO depends on your postcode. These are the main operators:
- UKPN (UK Power Networks) – London, South East, East England
- National Grid Electricity Distribution (formerly WPD) – Midlands, South West, Wales
- NPG (Northern Powergrid) – North East, Yorkshire
- SSEN (Scottish and Southern Electricity Networks) – Scotland, parts of Southern England
- ENW (Electricity North West) – North West England
- SP Energy Networks – Central and Southern Scotland, North Wales, Merseyside
You can find your DNO by entering your postcode via Energy Networks Association tools. Your MPAN also identifies the DNO: the first two digits are the DNO code. For UKPN customers only, generation guidance and contacts are on the UKPN DER generation page (example email G98_G99@ukpowernetworks.co.uk, phone 0203 324 1460). Your DNO may differ.
Submitting your application to the DNO
For G98 installations, submit the notification form within 28 days after commissioning. Include system technical specs and the schematic diagram. For G99 applications, submit the detailed form and await approval before installing. The DNO may ask for further information, so keep documents accurate to prevent delays.
Much of this process is online via the National Grid connections site, though some DNOs still use their own portals or email routes. Use the channel your DNO publishes for your postcode.
After DNO registration: export is a separate fork
DNO registration makes the generation connection legitimate. It does not open an export tariff by itself. To get paid for surplus from a DIY system, you still need a supplier process. With Octopus that means the non-MCS export route, certificates, and usually an export MPAN after the DNO letter is already in hand.
Next step when the DNO letter is done: follow how to export DIY solar energy with Octopus (no MCS). That page covers documents, timing, export MPAN versus DNO letter, and common failures.
Battery storage considerations
If you plan to add battery storage, especially systems with backup functionality that can island (disconnect from the grid during power outages), you must tell the DNO because those setups need additional safety checks. Battery storage is popular because it stores excess solar for later use, but it can change the connection details you declared. Re-notify if the connected arrangement changes materially.
Importance of timely and accurate applications
File promptly and accurately. DNOs have seen rising demand from renewable installs, and processing times can run longer than the brochure figures. For G98, expect the post-notification handling to take weeks rather than hours. For G99, plan for months on complex or constrained networks.
Common mistakes that delay your application
- Wrong MPAN number: check your bill, not a guess from the meter case
- Inverter not on the ENA Type Test Register: check before you buy on the ENA type test register. Need help picking the right one? See the inverter selection guide.
- Missing single-line diagram: draw it yourself; it does not need to be professional, but it does need to be complete
- Submitting G98 when you need G99: check total AC output per phase, not panel wattage alone
- Not allowing enough time for G99: some DNOs (for example SSEN) can take 45-60+ working days
- Expecting the DNO letter to start export payments: that is a supplier + export MPAN job; see the export guide
Final thoughts
Navigating the DNO application process is a core part of a safe, compliant DIY solar connection. Understand the AC limit, gather the right documents, and engage early if you are on the G99 path. When registration is complete, fork to export if you want to earn from surplus: register DIY export with Octopus. For the wider money picture, see UK solar panel grants and incentives 2026.
