Last updated 19 October 2026 · BrightEdge Solar team
Short answer: For most commercial solar and battery systems, the G99 process adds about 8–12 weeks before installation can start. The main wait is the network operator’s (DNO’s) connection offer. The guaranteed standard is 45 working days for a low-voltage (LV) generation quotation and 65 working days at high voltage (HV), counted from a complete application.[1] Network constraints, reinforcement work or an incomplete application can push it out. Export limitation or sizing to an existing approval can bring it in.
If you’re planning a commercial roof array, G99 is usually the stage that sets the start date. This guide covers each stage, the realistic timescales, and what we do to keep it moving on Northern Powergrid’s network in Yorkshire and the North East.
Key facts
- G98 vs G99: G98 covers small, fully type-tested systems up to 16 A per phase, about 3.68 kW single-phase or 11.04 kW three-phase. Anything larger, or anything not type-tested, falls under G99.[2][3]
- G98 is “connect and notify”: the installer notifies the DNO within 28 days of commissioning.[2]
- G99 is “apply first”: the DNO has to approve the connection before the system is connected.[3]
- Forms (ENA standard forms):
- up to 50 kW three-phase / 17 kW single-phase: Form A1-1
- above that: the Standard Application Form[3]
- Quotation standards (2026/27):
- LV generation quotation within 45 working days; HV within 65 working days
- the DNO pays £85 (LV) or £180 (HV) per working day late
- a budget estimate for under 1 MVA within 10 working days[1]
Do you need G99 at all?
Almost every commercial system does. A 30 kWp workshop roof on a three-phase supply will normally have an inverter rated well above 11.04 kW, so it’s G99.
Size is set by the inverter’s rating, not the panels. NGED’s guidance gives the example of a 4 kW single-phase inverter: that is 17.39 A, so it’s just over the G98 limit.[3] Adding a battery counts towards the total too. A hybrid inverter or battery inverter that can export adds to the generating capacity the DNO looks at.
The G99 timeline, stage by stage
| Stage | What happens | Typical time |
|---|---|---|
| 1. Data and survey | Half-hourly data or 12 months of bills, a supply check (fuse size, phases, existing generation, any existing G99 approval), roof survey | Depends on the site and how quickly the data is available |
| 2. Design and application | We design the array, choose inverters from the ENA Type Test register, draw the single-line diagram and decide whether export limitation is needed. Then we submit Form A1-1 or the Standard Application Form | Depends on the site and how quickly the data is available |
| 3. Optional budget estimate | If you want an early idea of cost and feasibility before committing to a full application | up to 10 working days (under 1 MVA)[1] |
| 4. DNO assessment and connection offer | The DNO studies the local network and issues an offer: full export, a limited export, or network work at a cost | up to 45 working days at LV, 65 at HV, from a complete application[1] |
| 5. Acceptance | You review the offer (and pay any connection charge). Offers have a validity period, so don’t let it lapse | your decision; days to weeks |
| 6. Installation | Panels, inverters and protection fitted to the approved design | days to weeks, depending on size |
| 7. Commissioning and notification | G99 tests, then the commissioning paperwork goes to the DNO. Larger or non-type-tested systems may have witnessed tests | Form A3-1 is submitted after commissioning[3] |
The 45-working-day standard is about nine calendar weeks. That’s why our own guidance says G99 “typically adds 8–12 weeks before installation”. Most of that time is the DNO’s study. We can’t shorten that, but we can make sure the clock starts as early as possible.
What makes G99 take longer
- An incomplete application. The standard runs from when the DNO has everything it needs. Missing type-test references, an unclear single-line diagram or the wrong MPAN all restart the wait. Our checklist covers these before submission.
- Network constraints. If the local substation or feeder has no headroom, the offer may include reinforcement at a cost, with its own timescale, sometimes much longer than the study itself.
- HV connections. Sites with their own HV supply or transformer fall under the 65-working-day HV standard.[1] Expect more questions and possibly witnessed testing.
- Design changes after submission. Changing inverter size or adding a battery after the offer can mean a revised application.
- Letting the offer lapse. Missing the acceptance deadline can mean starting again.
How to keep G99 short: export limitation and existing approvals
The quickest G99 is often one that asks the network for less:
- Size to an existing approval. On an 86 kWp industrial roof in Doncaster, the site already had a G99 approval for an older 60 kW inverter. We chose a SolarEdge SE66.6K Synergy inverter to fit within it. A SolarEdge ONE Commercial Controller manages G99/G100 export limitation, so the new array could go in without a fresh fight for capacity.
- Export limitation (G100). A certified export limiting scheme caps what flows back to the grid while you still use everything you generate on site. On our ground-mounted barn conversion system near Pocklington, a Solis Export Power Manager gives adjustable export-limit control with real-time power data.
- Add a battery. Surplus solar goes into storage instead of being exported, which can make a limited export offer workable. See battery storage.
- Apply early. We submit as soon as the design is agreed, in parallel with planning or roof checks, rather than after.
Northern Powergrid specifics
In Hull, East Yorkshire, North and West Yorkshire and the North East, the DNO is Northern Powergrid. Lincolnshire and the Midlands are mostly NGED, and the North West is Electricity North West. All of them use the same ENA G98/G99 rules and forms, and all are bound by the same Ofgem guaranteed quotation standards.[1][3] What differs is local network headroom. That’s why two similar roofs a few miles apart can get very different offers.
At 257 kWp, a system like the Integra Buildings roof in Paull (220 kW of inverter capacity) is well above the 50 kW threshold, so it goes through the Standard Application Form route rather than Form A1-1.[3] The case study lists a Solis Export Power Manager, which gives adjustable export-limit control.
G99 for batteries and system extensions
- Adding a battery to existing solar: if the combined export capability goes above the G98 limits, it’s a G99 matter, or at least a notification of change. We check this as part of any battery retrofit.
- Extending an existing array: the DNO looks at the total generation on the site, so a second array is assessed with the first.
- Multiple units on one estate: each grid connection is assessed separately. On a 300.06 kWp estate in Peterborough, we managed three grid connections on one occupied site.
FAQ
How long does G99 approval take?
Typically 8–12 weeks before installation for a commercial system. The DNO’s guaranteed standard is 45 working days for an LV generation quotation and 65 working days at HV, from a complete application.[1]
What’s the difference between G98 and G99?
G98 is for fully type-tested systems up to 16 A per phase (about 3.68 kW single-phase or 11.04 kW three-phase), and you notify the DNO within 28 days of commissioning. G99 covers anything larger and must be approved before connection.[2][3]
Which G99 form do I need?
Form A1-1 for systems up to 50 kW three-phase or 17 kW single-phase. The Standard Application Form above that.[3] We complete and submit it for you.
Can I install before G99 is approved?
You can plan and order, but the system mustn’t be connected and run in parallel with the grid until the DNO has approved it.[3] We schedule the install to follow the offer.
What if the DNO says no?
It usually says “yes, with conditions”: a lower export limit or network work at a cost. Export limitation (G100), a battery or a smaller inverter can often make the project work within the limit.
Start the clock early
We handle the whole G99 process as part of every commercial project: the supply check, design, application, DNO queries, commissioning and paperwork. Any DNO charges are shown separately in your quote. Send us your half-hourly data and supply details, and we’ll tell you whether you’re looking at G98, a simple G99 or a constrained connection.
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Sources
- Ofgem, Adjustments to the Guaranteed Standards of Performance prescribed sums (letter of 13 March 2026, Annex 1: DG standards 1A, 3A, 3B): https://www.ofgem.gov.uk/sites/default/files/2026-03/Guaranteed%20Standards%20of%20Performance%20payment%20update%202026.pdf (checked 19 Oct 2026)
- National Grid Electricity Distribution, Micro generation single (G98): https://connections.nationalgrid.co.uk/get-connected/solar-and-wind/micro-generation-single-g98 (checked 19 Oct 2026)
- National Grid Electricity Distribution, G99 connection procedures (ENA forms A1-1, Standard Application Form, A3-1; inverter rating example): https://connections.nationalgrid.co.uk/g99-connection-procedures (checked 19 Oct 2026)
- Energy Networks Association, distributed generation connection guides and G99/G100: https://www.energynetworks.org/
