DNO Approval Explained: G98 vs G99 Grid Applications for UK Solar & Batteries

What is a DNO and Why Do They Control Your Solar?

When installing rooftop solar panels or a home battery system, your system will be connected in parallel with the British National Grid. Whenever your solar panels generate more electricity than your home is consuming, that surplus power flows out through your consumer unit into the local low-voltage power lines in your street.

Because excessive, unregulated power export can destabilise grid voltage, cause local transformer overload, and endanger linesmen working during power cuts, all grid-tied generation in the UK is legally regulated by the Energy Networks Association (ENA) under engineering recommendations G98 and G99.

Who is Your DNO?

There are 6 licensed Distribution Network Operators operating across 14 geographic distribution regions in the UK:

1. National Grid Electricity Distribution (NGED): Midlands, South Wales, and the South West.
2. UK Power Networks (UKPN): London, South East England, and East of England.
3. SP Energy Networks (SPEN): Central & Southern Scotland, Merseyside, Cheshire, and North Wales.
4. Northern Powergrid (NPg): North East England, Yorkshire, and northern Lincolnshire.
5. Scottish and Southern Electricity Networks (SSEN): Northern Scotland and Central Southern England.
6. Electricity North West (ENW): North West England (Manchester, Lancashire, Cumbria).

---

G98: The “Fit and Inform” Pathway (Up to 3.68kW)

Engineering Recommendation G98 is the simplest and fastest regulatory route for domestic installations:

• Capacity Threshold: Applies to micro-generators with a maximum AC export capacity of up to 16 Amps per phase, which equates exactly to 3.68kW on a standard 230V single-phase UK domestic supply (or 11.04kW on a three-phase supply).
• The “Fit and Inform” Procedure: Under G98, your MCS-certified installer does not need prior permission from the DNO to install the system.
• The Process: The installer mounts your solar panels, connects the 3.68kW inverter, tests the electrical circuits, commissions the system, and leaves it turned on. The installer then has 28 days following commissioning to submit a standard G98 commissioning form to the local DNO.
• Cost: Free of charge. DNOs do not charge fees for G98 notifications.

---

G99: The “Apply and Wait” Pathway (Above 3.68kW)

If your system’s combined AC inverter capacity exceeds 3.68kW per phase, it automatically falls under Engineering Recommendation G99:

• Why Domestic Systems Exceed 3.68kW: Modern family homes frequently install 5kW or 6kW hybrid inverters paired with 12 to 16 panels, or have separate AC-coupled battery storage inverters operating alongside their solar inverter.
• The “Apply and Wait” Procedure: Under G99, your installer must submit a formal network connection application and receive written consent from the DNO before the system is turned on.
• Timeline: DNOs have a statutory window of up to 45 working days (typically 4 to 8 weeks) to review your application, run load-flow simulations on the local street substation, and issue formal connection terms.

---

G99 Application Types: Fast Track vs Standard

Application Pathway	Inverter Capacity Range	Typical Approval Timeline	DNO Application Fee
G98 Notification	Up to 3.68 kW (16A Single Phase)	Instant (Commission & notify in 28 days)	£0 (Free)
G99 Fast Track (A1-1)	3.69 kW to 5.0 kW (with approved G100 device)	10 to 20 Working Days	£0 to £150
Full G99 (Standard)	Above 5.0 kW (or multi-inverter setups)	4 to 10 Weeks	£250 to £600+ (if network study needed)

---

What Happens if the Local Grid is Congested? (G100 Export Limitation)

In certain suburban cul-de-sacs or rural villages with high solar adoption, local transformers may already be operating near thermal capacity on bright summer afternoons. If your DNO determines that your street cannot absorb another 5kW of exported power, they will not reject your installation. Instead, they will issue conditional G99 approval with an export cap:

How G100 Export Limitation Works:

• Your installer fits a certified G100 Export Limitation Device (a certified smart energy meter connected to your hybrid inverter).
• Your solar panels can continue generating at their full 5kW or 6kW capacity to power your home and charge your battery.
• However, the G100 device monitors the grid connection point: if domestic demand is low and export threatens to exceed the DNO’s permitted limit (e.g. 3.68kW), the inverter instantly ramps down generation to protect the local transformer.

---

Who Handles the DNO Paperwork?

You do not need to deal with the DNO directly.

Under MCS (Microgeneration Certification Scheme) regulations, your accredited installation company is legally responsible for preparing the single-line electrical diagrams, specifying the inverter ENA Type Test register numbers, and submitting the G98 or G99 documentation to your regional network operator.

Once approval is granted, your installer will provide you with a copy of the DNO Acceptance Letter and your MCS Certificate, both of which are mandatory requirements for registering with licensed energy suppliers (such as Octopus Energy or British Gas) to claim your Smart Export Guarantee (SEG) feed-in payments.