DNO Grid Connection Guide for Commercial Solar
Understanding the Distribution Network Operator process is essential for commercial solar projects. This guide covers G98, G99, all UK DNOs, protection relays and how to avoid costly delays.
Quick Answer
What DNO grid connection approval do I need for commercial solar?
Commercial solar systems up to 50kWp require a G98 notification to your DNO (notified within 28 days of commissioning). Systems above 50kWp require a G99 application, which must be approved before installation. G99 approval takes 8-16 weeks depending on your DNO and connection point. We submit G99 applications on the day of contract signature to avoid project delays.
What is a DNO and Why Does It Matter for Commercial Solar?
The Distribution Network Operator (DNO) owns and operates the cables, substations and infrastructure that distribute electricity from the National Grid transmission system to homes and businesses. When you install a commercial solar system that connects to the grid — either to export surplus electricity or simply to remain grid-connected — you must notify or apply to your local DNO.
The DNO connection process is one of the most misunderstood aspects of commercial solar installation. Many businesses receive quotes from installers that omit or underestimate DNO costs and timelines, leading to project delays and cost overruns. Understanding the process empowers you to plan accurately, budget correctly and select installers who manage DNO applications competently.
The UK has seven regional DNOs, each responsible for a specific geographic area. They operate under Ofgem regulation and must follow common engineering recommendations (primarily Engineering Recommendation G98 and G99) for connecting generation equipment to the distribution network.
The Seven UK Distribution Network Operators
| DNO | Region Covered | Connections Portal | Key Notes |
|---|---|---|---|
| National Grid Electricity Distribution (NGED) | East and West Midlands, SW England, South Wales | nged.com/connections | Largest DNO by area; formed by WPD acquisition 2022 |
| Electricity North West (ENW) | North West England (Manchester, Merseyside, Cumbria) | enwl.co.uk/connections | Active solar connections programme; good pre-app support |
| Northern Powergrid (NPg) | Yorkshire, NE England, parts of Lincolnshire | northernpowergrid.com | Two licence areas: Yorkshire and Northeast |
| UK Power Networks (UKPN) | Greater London, SE England, East of England | ukpowernetworks.co.uk/connections | Busiest DNO by connection volume; good online portal |
| SP Manweb | Merseyside, Cheshire, North Wales | spenergynetworks.co.uk | Part of SP Energy Networks; overlaps with ENW in Merseyside |
| SSEN (Southern Electric Power Distribution) | South England, Scottish Highlands and Islands | ssen.co.uk/connections | Two separate licence areas: south and north Scotland |
| SP Energy Networks (SPEN) | Central Scotland, South Scotland | spenergynetworks.co.uk | Part of SP Energy Networks; covers Glasgow, Edinburgh areas |
Your DNO is determined by the location of the property. Enter a postcode on the Energy Networks Association (ENA) website (energynetworks.org) or use the Ofgem postcode lookup to identify your DNO. All connections enquiries, applications and technical queries go to your regional DNO.
G98: Notification for Micro and Small-Scale Generation
Engineering Recommendation G98 covers the connection of generating equipment up to 50kW (single unit) or 50kW aggregate per phase to the low-voltage (LV) distribution network (typically 230V single-phase or 400V three-phase). For most small commercial solar installations up to 50kW, the process is straightforward notification rather than application.
G98 Process
- The installer notifies the DNO before connection (at least 5 business days in advance)
- Notification includes: location, technology type, rated capacity, installer details
- The DNO does not approve or reject G98 notifications — it is a notice, not an application
- The inverter must comply with BS EN 62116 anti-islanding requirements
- The inverter is typically configured to disconnect within 2 seconds if grid frequency or voltage goes outside defined limits
For systems between 3.68kW and 50kW per phase, the G98 process requires the installer to complete a commissioning check and provide the DNO with a commissioning data sheet after installation. This confirms the protection settings are correctly configured.
G99: Application for Systems Over 50kW
Engineering Recommendation G99 applies to all generation systems over 50kW connecting to the distribution network. Unlike G98 notification, G99 requires a formal application and approval from the DNO before connection. The DNO must assess the impact of the generation on the local network and may impose conditions on the connection.
G99 Application Stages
| Stage | Description | Typical Timeline | Cost |
|---|---|---|---|
| Pre-application enquiry | Optional but recommended; discuss project with DNO before formal application | 2–4 weeks | Usually free |
| Formal G99 application | Submit application form, system design, single-line diagram, proposed protection relay spec | Application submitted | Application fee: £300–£1,500 |
| DNO technical review | DNO assesses network impact, load flows, fault level, protection coordination | 4–12 weeks | Included in study fee |
| Connection offer (ICP) | DNO issues Infrastructure Connection Proposal with connection terms and cost | With review outcome | Study fee: £2,000–£20,000 |
| Accept ICP and pay works cost | Business accepts connection offer and pays any network works contribution | Within offer validity period | Works cost: £0–£300,000+ |
| Protection relay installation | Installer installs Type A/B/C relay and export metering | Included in solar install | Relay cost: £1,500–£5,000 |
| Commissioning and RCPD | Final connection testing and protective device commissioning | 1 day | Included in installer quote |
Protection Relays Under G99
All G99-connected solar systems must include a protection relay that disconnects the solar system from the grid in the event of grid faults, islanding conditions or out-of-range voltage/frequency. The relay type depends on system size:
| System Size | Relay Type | Key Function | Typical Cost |
|---|---|---|---|
| 50kW–1MW (LV) | Type A interface protection | RoCoF, V/f protection, loss of mains | £1,500–£2,500 |
| 1MW–10MW (HV) | Type B interface protection | Full directional overcurrent, distance protection | £4,000–£12,000 |
| >10MW | Type C interface protection | Full transmission-grade protection suite | Project-specific |
Type A relays are standard for commercial solar systems under 1MW. Modern inverters from SolarEdge, SMA, Fronius and Huawei increasingly incorporate G99 Type A protection functionality within the inverter itself, eliminating the need for a separate relay unit and reducing installed cost.
Export Limiting: How and Why DNOs Impose Constraints
In some areas of the UK, local substations are operating close to their rated capacity. Adding significant embedded generation (solar systems exporting to the grid) can cause voltage rise and overloading of local cables and transformers. When this is the case, DNOs impose an export limit — restricting the maximum power the solar system can export at any given time.
Export limiting does not prevent the solar system from generating. It prevents the system from exporting above the agreed limit at any time. Self-consumed electricity is unaffected by export limits — the limit only applies to the quantity sent out to the grid.
Export limiting is implemented by an Export Limitation Controller (ELC), an active device that monitors the export meter and signals the inverter to reduce output (curtail) when the export threshold is being approached. Modern inverters with Modbus TCP/IP or SunSpec communication integrate directly with ELCs without additional hardware.
Strategic Design Response to Export Limits
When a DNO imposes a 50kW export limit on a 200kW solar system, the optimal response is battery storage — charging the battery from generation above the export limit, rather than curtailing it. This recovers economic value from generation that would otherwise be wasted. We model battery sizing against DNO export limits as a standard part of constrained connection projects.
DNO Connection Costs: What to Expect by Region
Connection costs vary enormously depending on distance to a suitable connection point, substation capacity, and whether network reinforcement is required. The following ranges are indicative for a 200–500kW commercial solar system:
| Cost Category | Low End | High End | Driver |
|---|---|---|---|
| G99 application study fee | £2,000 | £20,000 | DNO engineering staff hours; project complexity |
| Protection relay (Type A) | £1,500 | £3,000 | Relay specification; integration with inverter |
| Export metering | £500 | £2,000 | CT metering; DNO-approved meter |
| Network reinforcement | £0 | £300,000+ | Distance from substation; substation capacity |
| Service connection upgrade | £1,000 | £25,000 | Upgrading supply cable for bi-directional power flow |
| Total DNO cost (no reinforcement) | £5,000 | £30,000 | Typical for urban/suburban commercial sites |
| Total DNO cost (with reinforcement) | £30,000 | £300,000+ | Rural sites; industrial zones at capacity |
We obtain a pre-application DNO enquiry on every project over 50kW before design finalisation. This identifies any potential reinforcement requirement and allows the project economics to be reassessed before significant design or procurement costs are incurred.
Timelines: Planning Your Solar Project Around DNO
The DNO application timeline is typically the longest single-stage constraint in a commercial solar project. Physical installation of a 200kW system takes 5 days — but G99 approval can take 3–4 months. Effective project management means starting the DNO application process as early as possible, ideally within 2 weeks of the feasibility survey.
| Project Size | DNO Standard | Application to Offer | Key Risk |
|---|---|---|---|
| Under 3.68kW | G98 notification | 2 weeks | Minimal risk |
| 3.68–50kW | G98 notification | 2–6 weeks | Minimal risk |
| 50kW–1MW | G99 application | 8–16 weeks | DNO technical queries extend timeline |
| 1MW–5MW | G99 with load flow study | 16–36 weeks | Network reinforcement may be required |
| >5MW | G99 / connection agreement | 36–104 weeks | Full network planning study required |
Working with Your Installer on DNO Applications
G99 applications require specific technical documents including system single-line diagrams, protection relay specifications, and export metering schedules that can only be prepared by a qualified electrical designer. Ensure your installer has demonstrated experience with G99 applications before committing to a project.
Questions to ask your solar installer regarding DNO process:
- Who prepares your G99 application — in-house or subcontracted?
- Have you connected systems to [specific DNO] before?
- What is your standard protocol for obtaining pre-application enquiries?
- Can you provide a reference contact for a recent G99-connected project?
- How do you handle projects where DNO reinforcement costs emerge during the process?
We prepare all G99 applications in-house, maintain working relationships with connections officers at all seven UK DNOs, and have successfully navigated reinforcement requirements, export limitations and complex parallel substation studies across hundreds of commercial solar projects.
Case Studies
Case Study: 400kW Logistics Park, NGED Area, No Reinforcement
A logistics operator applied for G99 connection to NGED for a 400kW array. Pre-application enquiry (2 weeks) confirmed substation had sufficient headroom. Formal G99 application to NGED: submitted Week 3. DNO technical review: 11 weeks. Connection offer: no reinforcement required, Type A relay, £6,500 metering and relay costs. Connection date allocated. Solar install: 6 days. Total project timeline survey to generation: 18 weeks.
Case Study: 200kW Factory, ENW Area, Export Limited at 100kW
A manufacturing company applied to ENW for a 200kW G99 connection. ENW imposed a 100kW export limit due to transformer headroom constraints. Solution: 150kWh LFP battery storage with ELC — absorbs surplus above 100kW rather than curtailing. Net result: 95% of generation is self-consumed or stored. Export limit rendered effectively irrelevant. Annual energy saving: £41,000 vs £28,000 without battery. Battery added £45,000 to project cost but recovered in 4 years.
Case Study: 1.2MW Industrial Estate, UKPN, Complex Study
A commercial property owner sought G99 for a 1.2MW rooftop array across 8 buildings. UKPN required a full load flow study (£18,000 study fee). Study identified need for 11kV transformer upgrade (£85,000 DNO works contribution). Despite the DNO costs, project economics remained strong: annual saving £216,000, full payback (including DNO works) 6.8 years, IRR 14%.
Frequently Asked Questions
What is a DNO?
The DNO (Distribution Network Operator) owns and operates the local electricity distribution cables and substations. All commercial solar connections must be notified to or approved by the local DNO.
Do I need G98 or G99 for my solar system?
G98 notification applies to systems up to 50kW. G99 full application applies to systems over 50kW. Your installer handles the application as part of the installation project.
How long does DNO approval take?
G98 notifications take 2–6 weeks. G99 applications for systems under 1MW typically take 8–16 weeks from submission to approval. Rural or large projects can take 6–18 months if network reinforcement is required.
Can the DNO reject my solar connection?
The DNO cannot refuse connection but can impose conditions (export limits, protection relay specifications, metering requirements) and charge for any network works required. In practice, most commercial solar systems under 500kW connect without major issues.
What does export limiting mean?
Export limiting restricts the maximum power your solar system can send to the grid. Self-consumption is unaffected. Adding battery storage is the most effective response to an export limit — storing generation above the limit rather than curtailing it.
Get Expert DNO Guidance
Our team has handled hundreds of G99 applications across all UK DNO areas. We navigate the DNO process on your behalf, from pre-application enquiry to commissioning.
Get a Free SurveyG99 Application Timeline by DNO
G99 processing times vary significantly by DNO and connection point. Here are current typical timescales (2026) based on our project experience:
| DNO | Region | G99 Pre-application | G99 Approval | Portal |
|---|---|---|---|---|
| NGED | Midlands, Yorkshire, East Anglia, South West | 2-3 weeks | 8-12 weeks | nged.com/connections |
| UKPN | London, South East, East of England | 3-4 weeks | 10-14 weeks | ukpowernetworks.co.uk |
| ENW | North West England | 2-3 weeks | 8-12 weeks | enwl.co.uk/connections |
| Northern Powergrid | Yorkshire, North East | 3-5 weeks | 10-16 weeks | northernpowergrid.com |
| SP Energy Networks | Central Scotland, Merseyside | 3-4 weeks | 10-14 weeks | spenergynetworks.co.uk |
| SSEN | South England, Scotland Highlands | 2-4 weeks | 8-14 weeks | ssen.co.uk/connections |
Can I install commercial solar before G99 approval?
No. G99 approval must be received before commissioning a commercial solar system above 50kWp. Installing before approval breaches your DNO connection agreement and voids your inverter warranty. Export must also not commence before the formal G99 approval notice. We submit G99 applications at contract signature — typically 8-14 weeks before installation — so approval is in hand before installation begins.
Does a G99 application cost money?
G99 applications themselves are free to submit (the DNO charges no application fee). Connection costs may apply if the DNO needs to reinforce the local network, which can range from nil for urban sites with spare capacity to £20,000-£100,000 for rural locations requiring network upgrades. We obtain a pre-application assessment from the DNO as part of every commercial solar project to identify any connection costs before you commit.
We manage your G99 DNO application — start to approval
Our G99 application service covers all UK DNOs. We submit on contract signature, track progress, respond to DNO technical queries, and programme your inverter protection relay to the approved settings. No G99 experience required on your part.
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