What is the difference between G98 and G99 applications?

G98 and G99 are the two Engineering Recommendation standards governing how generators (including solar PV) connect to the UK electricity distribution network. They’re issued by the Energy Networks Association (ENA) and used by all UK Distribution Network Operators. G98 covers small installations up to 16 A per phase — typically up to 3.68 kW single-phase or 11.04 kW three-phase per installation, sometimes higher in dual installations. G99 covers everything larger. The two standards have very different timelines: G98 is a “connect and inform” process taking 4-8 weeks; G99 is a full design and approval process taking 6-18 months. For most SME projects above 50 kW, G99 applies — and the DNO timeline becomes the longest single item in the project schedule.

G98: small embedded generation

G98 (Engineering Recommendation G98 Issue 1, originally G83) governs micro-generation connections. Eligibility:

• Single dwelling: up to 16 A per phase (3.68 kW single-phase, 11.04 kW three-phase)
• Multiple dwellings on same network: aggregate considered
• Equipment must be type-approved per ENA G98 Type Test Verification Report

Process:

1. Installer completes commissioning
2. Installer submits G98 notification to DNO within 28 days of commissioning
3. DNO acknowledges; no design approval required
4. System operates immediately

Timescale: effectively instant once installed. Notification is administrative.

Best for: small office solar (sub-12 kW), domestic rural workshops, micro-business installs.

G99: medium and large embedded generation

G99 (Engineering Recommendation G99 Issue 1 Amendment 9) governs everything bigger. Eligibility includes:

• Any single install above the G98 threshold
• Any aggregation of generators on same network exceeding the threshold
• Battery energy storage systems

Process:

1. Installer prepares G99 application (about 25-50 pages of design data)
2. Submit to DNO with fee (£300-£1,500 depending on DNO and capacity)
3. DNO conducts feasibility study
4. DNO issues connection offer, possibly with conditions/upgrades
5. Customer accepts offer, signs Connection Agreement, pays connection charge
6. Pre-installation tests
7. Witnessed commissioning by DNO engineer
8. System operates

Timescale: 6-18 months from application to connection. Constrained network areas (parts of east of England, south coast, Scottish highlands) sometimes longer.

Best for: anything above 17 kW. The vast majority of SME commercial solar above 50 kW.

DNO timescales — what to expect

DNO	Typical G99 timescale
UK Power Networks (London, East, Southeast)	8-14 months
Western Power Distribution (Midlands, SW, Wales)	6-12 months
Northern Powergrid (Yorkshire, NE)	8-13 months
Electricity North West	10-18 months
SP Energy Networks (Scotland, Manweb)	12-18 months
SSE (Scotland, Southern)	8-15 months

Variation is high. Constrained areas (network full of existing generation) take much longer. Greenfield distribution can be quick.

What G99 connection charges look like

The connection charge depends on what the DNO needs to do to accept your generation:

• Pure software/admin: £300-£1,500 (lucky)
• Local network reinforcement (a couple of substations need uprating): £5,000-£25,000
• Transformer upgrade: £25,000-£100,000
• HV reinforcement (large 11kV+ work): £100,000-£500,000+
• Brand new 11kV connection: £250,000-£2m

For SME-scale projects (50-500 kW), most connection charges land in the £2,000-£25,000 range. Beyond 500 kW the charges spike materially.

Strategies to reduce G99 pain

1. Submit early: file the G99 application as soon as feasibility is confirmed, even before contract. The DNO timeline starts on submission.
2. Curtailment as a pre-condition: agreeing to curtail export above a certain threshold can avoid network reinforcement and reduce connection charges.
3. Storage to absorb peak generation: batteries that absorb peak generation reduce export to the grid and may avoid reinforcement.
4. Stay below G99 threshold: if your site can be split into multiple G98 connections (rare and complex), you can avoid G99. Only viable for some configurations.

Worked example: 80 kW system on a Manchester light-industrial unit

Site: 1990s steel-portal building. Existing supply: 250 kVA three-phase. Local network: moderately loaded.

Application filed week 1. DNO feasibility complete week 14. Offer received: £4,200 connection charge, no major reinforcement, single substation uprate. Offer accepted week 16. Connection completed week 28.

Total G99 timeline: 28 weeks (6.5 months). Within typical range.

Common misconceptions about G98/G99

“G99 applies above 100 kW” — wrong. G99 applies above 16 A per phase (~17 kW three-phase, ~3.68 kW single-phase). Most SME commercial solar above 17 kW is G99.

“G98 sites can be larger if you split them” — only with separate metering and network points of common coupling. Splitting one site’s generation across multiple G98 applications usually triggers DNO aggregation rules.

“DNO timescales are negotiable” — partially. You can pay an “accelerated connection charge” with some DNOs to jump the queue, but only if the network has capacity. No amount of money speeds up reinforcement work itself.

“You can install before DNO approval” — never. Operating embedded generation without DNO approval is a breach of the Distribution Code and your licence.

Next steps

For a feasibility study including DNO timeline forecast, contact us. See planning permission rules, building regulations, cost guide, and grants and funding.