G98 vs G99 DNO Applications Explained: A Practical Guide
How G98 and G99 grid connections work for UK commercial solar in 2026. Application process, timescales (G98: 4-8 weeks, G99: 6-18 months), costs and pitfalls.
If your commercial solar project gets stuck for 9 months and nobody can quite explain why, the answer is almost always the DNO. The Distribution Network Operator manages the local public network in your region, and any new generator connecting to that network must follow Engineering Recommendations G98 (sub-100 kW) or G99 (above 100 kW). For a 50 kW office system the application is a formality. For a 250 kW factory roof, it is the dominant pole on your project Gantt chart.
This guide explains how G98 and G99 actually work in 2026, the realistic timescales, the costs, who pays for what, and the pitfalls that derail projects.
DNOs in 2026: the six regional networks
The UK has six DNO licence areas, each operated by one of three companies plus several smaller IDNOs:
| Region | DNO | Coverage |
|---|---|---|
| London | UK Power Networks | London, plus East and South East England |
| East / South East | UK Power Networks | Essex, Hertfordshire, Bedfordshire, Norfolk, Suffolk, Kent, Sussex, Surrey |
| West / South West | National Grid Electricity Distribution (NGED, formerly WPD) | Wales, West Midlands, South West, East Midlands |
| North West | Electricity North West | Cumbria, Lancashire, Greater Manchester |
| Yorkshire / North East | Northern Powergrid | Yorkshire, Tyne & Wear, Durham, Northumberland |
| Scotland | SP Energy Networks (south) / SSEN (north) | Central / South / Highlands & Islands |
Plus several Independent DNOs (IDNOs) — Last Mile, ESP Electricity, GTC, Energy Assets — typically operating new-build estate networks.
Find your DNO via Energy Networks Association’s DNO postcode lookup.
What G98 covers — sub-100 kW connections
G98 is the engineering recommendation for “Type Tested” installations of small inverters connecting in parallel with the public network. In practical terms:
- Capacity threshold: Up to 16 A per phase (about 3.68 kW single-phase or 11.04 kW three-phase) per inverter, with multiple inverter installations permitted up to a total system limit, currently set per DNO but usually equivalent to ~100 kW total at the connection.
- Type-tested equipment only. The inverter must hold a G98 type-test certificate. Installer ticks the make/model from a list.
- Notification, not application. G98 is a notification to the DNO after commissioning. You don’t ask permission, you tell them you’ve connected.
- Timescale: Practical end-to-end timeline 4–8 weeks (notification, acknowledgment, MCS certificate). The DNO has 28 days to respond.
- Cost: Typically zero for the connection itself. The DNO charges nothing for a sub-100 kW G98 notification.
For most office, small school, hotel, retail, hospitality and small-warehouse installations under 100 kW total inverter capacity, G98 is the route. Your installer handles the paperwork. You should never pay extra for a G98 application — it is administrative.
What G99 covers — above 100 kW
G99 is the engineering recommendation for installations above the G98 threshold, including all serious commercial PV. In practical terms:
- Capacity: Above the G98 ceiling, up to and including 50 MW connections (above 50 MW falls under transmission system rules).
- Application, not notification. You apply before construction. The DNO reviews network capacity, may require studies, issues a connection offer with conditions and a price.
- Timescale: 6–18 months end-to-end is realistic. Some areas (parts of East Anglia, parts of South East England, parts of the M4 corridor) currently take longer due to network constraint.
- Cost: Variable — from £1,500 administration fee for a fully accommodating connection up to £80,000+ where DNO reinforcement is required (transformer upgrade, switchgear addition, cable upgrade).
The G99 process splits into two design tiers:
G99 Type A — installations between roughly 100 kW and 1 MW. Typically grid-connected via a 11 kV or 6.6 kV interface. The application uses standard inverter type-test certificates plus protection settings declaration. Studies are usually network-load only.
G99 Type B / C / D — above 1 MW or where the inverter is non-type-tested. Requires more detailed engineering studies including dynamic performance (LVRT, fault ride-through, voltage support). Additional documentation, witness commissioning often required.
For most UK SME projects, Type A is the operative tier.
The G99 application process — step by step
-
Pre-application screening. Optional but free DNO portal check. UK Power Networks (
uk-power-networks.co.uk), NGED (nationalgrid.co.uk/electricity-distribution), Northern Powergrid, ENWL, SP Energy Networks and SSEN all have online generator capacity heatmaps. Check before designing the system — if your site is in a deeply constrained area, the project economics change. -
Formal application. Online portal in most regions. Required information:
- Site MPAN
- Connection point single-line diagram
- Inverter make / model / quantity
- Total export capacity (kW AC at the point of connection)
- Protection settings declaration
- Project programme
-
Network study. The DNO models the connection against local network constraint. If existing capacity exists, a “no reinforcement” offer is issued. If not, the offer specifies reinforcement works and pricing.
-
Connection offer. Typically valid for 90 days. Specifies:
- Connection charge (one-off cap-ex)
- Use of System charges (operating cost)
- Required protection
- Required commissioning witness
- Commissioning date constraints
-
Acceptance. You pay the connection fee (or a deposit). DNO programmes the works.
-
Reinforcement / connection works. Anywhere from 4 weeks (no works) to 18 months (transformer or switchgear upgrade) depending on what’s specified.
-
Commissioning. DNO witness present (or remote sign-off for Type A). Final paperwork issued.
-
Energise. Plant begins exporting.
2026 timescale reality check
Headline G99 timescales are misleading because they range from “5 weeks total” for an unconstrained urban estate to “26 months” for a project in a constrained part of the South East waiting on transformer delivery. The realistic 2026 medians:
| Scenario | Realistic G99 timeline |
|---|---|
| Type A, no reinforcement, urban industrial estate | 8–14 weeks |
| Type A, minor reinforcement (cable upgrade) | 4–7 months |
| Type A, transformer upgrade required | 7–14 months |
| Type B, network study + reinforcement | 9–18 months |
| Constrained network area, Type B+ | 12–26 months |
For a factory installation, warehouse rooftop or hospital project, build the DNO timeline into the financial close — not the construction programme.
What “constrained” actually means
DNO heatmaps mark areas as “constrained” or “no available capacity” where existing demand and generation already loads the local substation to its limit. Adding generation requires either:
- Active Network Management (ANM) — accept a connection offer that allows the DNO to remotely curtail your export when the network is heavily loaded. ANM connection offers are cheaper but reduce annual export volume by 5–25% depending on the network.
- Reinforcement — pay for new local infrastructure (transformer, switchgear, conductor) to increase headroom. Cost ranges £30,000 to £400,000 for SME-scale projects.
- Wait — accept a connection offer with a delayed energisation date, sometimes 2–5 years out.
The constrained-area maps shift constantly. A site that was unconstrained in 2024 may now be constrained because three large generators connected in 2025. Always check the current state, not last year’s.
Costs you will see on a G99 quote
| Cost line | Typical 2026 range | Notes |
|---|---|---|
| Application fee | £700 – £1,500 | Refundable in some cases on acceptance |
| Connection charge (no reinforcement) | £1,500 – £5,000 | Standard administrative + commissioning |
| Connection charge (minor reinforcement) | £8,000 – £30,000 | Cable upgrade, switchgear addition |
| Connection charge (major reinforcement) | £40,000 – £400,000+ | Transformer, ring main extension |
| Witness commissioning | £500 – £3,000 | Type A is often remote; Type B usually requires on-site |
| ANM equipment | £2,000 – £15,000 | Remote curtailment hardware where required |
| Use of System (UoS) charges (annual) | £200 – £5,000 | Recurring, varies by region and capacity |
A standard mid-market 250 kW commercial install with no reinforcement should land at a total DNO cost between £3,500 and £8,500 in 2026. If your installer’s quote excludes DNO fees and your connection turns out to require £45k of reinforcement, the project economics shift materially — make this a contract risk allocation discussion.
Common pitfalls that derail G99 applications
- Submitting before site survey is complete. Inverter selection, layout and protection settings drive the application. A change after submission usually means resubmission and lost timeline.
- Inverter not on the type-tested list. Save 2–4 weeks by confirming type-test certification in advance.
- Underestimating ANM impact. Some installers downplay ANM curtailment. Ask for the DNO’s curtailment estimate and model the project IRR against it.
- Missing the offer-acceptance window. A 90-day offer expires. Re-issuance can take another 4–8 weeks.
- DNO reinforcement timescales not understood. Transformer manufacturers run 9–18 month lead times in 2026 — if reinforcement requires a transformer, the DNO is held by their supplier, not by you.
- Two parallel applications on the same site. Sometimes happens when an installer submits early for a different scope than the final design. Withdraw any duplicate before formal design lodgement.
How to compress the G99 timeline
You can’t cheat the queue, but you can stop wasting weeks:
- Start G99 in parallel with the rest of design. Don’t wait for full survey completion if you can submit a credible “design intent” application early.
- Accept ANM where viable. Trade 8% curtailment for 6 months saved on reinforcement.
- Pre-pay for technical studies. Some DNOs offer faster study completion for an additional fee.
- Use a specialist DNO consultant for projects above 500 kW. £2,000–£5,000 spent on a consultant can save 2–4 months.
- Check the heatmap before site selection. For new-build sites or expansion estates, this can be the difference between a 3-month and a 14-month connection.
Devolved differences
Scotland. SSEN-North operates the most constrained DNO area in the UK in 2026, with major projects subject to multi-year queues. Highlands and Islands grid reinforcement is a structural issue. SP Energy Networks (south Scotland) is more accommodating.
Wales. NGED covers most of Wales. Active Network Management is widely deployed in mid-Wales due to existing wind generation density.
Northern Ireland. NIE Networks runs the entire DNO area. Application process broadly mirrors GB but with separate engineering recommendations (DRAGON in some materials).
Bottom line
G98 is administrative — your installer handles it, you don’t pay, and timelines are 4–8 weeks. G99 is a distinct project workstream with its own programme, cost and risk profile. For any UK commercial project above 100 kW, treat the DNO application as a critical-path activity from week one, not an afterthought.
For a site-specific assessment that includes preliminary DNO heatmap check and likely connection cost, request a commercial solar quote. For sector-specific DNO patterns see warehouses, factories, data centres and logistics.