Every solar PV system connected to the UK grid must comply with one of two ENA Engineering Recommendations: G98 for systems up to 16A per phase, and G99 for larger systems. These are not optional guidelines — they are the legal framework that governs how generating equipment connects to the distribution network, backed by the Electricity Safety, Quality and Continuity Regulations (ESQCR).
Understanding G98 and G99 determines whether your installation requires only a prior notification or a formal DNO application with a 45-working-day review. Getting this wrong can mean installing a system that cannot be legally energised, a failed SEG registration, or — in the worst case — a network protection issue.
G98 and G99 Were Updated in Recent Years
G98 Issue 1 Amendment 6 and G99 Issue 1 Amendment 6 (published in 2022–2023) introduced changes to protection settings and requirements for battery storage. Always use the current amendment when specifying protection relay settings. Check the ENA website at energynetworks.org for the latest versions.
The UK Distribution Network: Who Are the DNOs?
Before submitting any notification or application, you need to know which DNO serves the installation address. There are six electricity distribution network operators in Great Britain (with separate arrangements in Northern Ireland):
| DNO | Coverage Area |
|---|---|
| UK Power Networks (UKPN) | South East England, East of England, London |
| Western Power Distribution (WPD) / National Grid ED | Midlands, South West, Wales |
| Electricity North West (ENW) | North West England |
| Northern Powergrid (NPG) | North East England, Yorkshire |
| SP Energy Networks (SPEN) | Central and Southern Scotland, Merseyside, North Wales |
| Scottish Hydro Electric Power Distribution (SHEPD) | North of Scotland |
| NIE Networks | Northern Ireland |
Each DNO has its own G98/G99 online submission portal and may have specific local requirements or standard conditions that apply on top of the national G98/G99 standards.
G98 vs. G99: Which Applies?
The dividing line is 16 amperes per phase of inverter AC output current.
| System Configuration | Threshold | Standard |
|---|---|---|
| Single-phase inverter | Up to 3.68 kW (16A × 230V) | G98 |
| Single-phase inverter | Above 3.68 kW | G99 |
| Three-phase inverter | Up to 11.04 kW (16A × 3 × 230V) | G98 |
| Three-phase inverter | Above 11.04 kW | G99 |
| Multiple units at same premises | Combined output determines threshold | G98 or G99 |
The combined capacity rule: If a property already has a G98 system installed, and you are adding a new system, the combined AC output determines which standard applies. A property with a 3 kW existing system plus a new 2 kW addition has a combined 5 kW output — which exceeds the G98 threshold on a single-phase property, triggering G99 for the addition.
Additions to Existing Systems Often Require G99
This catches many installers off guard. If a customer already has a G98-notified system and wants to add battery storage with a hybrid inverter, or add more panels, the combined output of all connected generation at the premises may push the total above 16A per phase. In this case the new addition — and potentially the entire system — needs a G99 application.
G100: DC-Coupled Battery Systems
G100 is a newer ENA recommendation that covers DC-connected battery storage systems connected on the DC side of an existing inverter. If you are installing a DC-coupled battery alongside an existing solar array:
- The battery system must be registered under G100
- G100 applies where the battery does not add additional AC export capacity to the inverter
- If the combined AC export capacity increases, G98 or G99 may also apply
The G98 Process: Notification Only
G98 is a notification process, not an approval process. The DNO does not have veto power over a G98 installation — they simply need to receive advance notice.
What to Submit
Complete the DNO’s G98 Notification Form
Each DNO has its own form or online portal. The information required is standardised across DNOs: installation address, MPAN (Meter Point Administration Number), inverter make and model, rated AC output in kW and A per phase, protection settings, MCS certificate number (if applicable), and intended commissioning date.
Submit at Least 28 Days Before Commissioning
G98 requires notification to be submitted no later than 28 calendar days before the system is energised. You can submit earlier — many installers submit at the time of signing the contract to ensure the timeline is met regardless of installation delays.
Wait for Any DNO Response
In the vast majority of cases, the DNO accepts the G98 notification without any specific response. However, if the DNO identifies a network constraint or has questions about the protection settings, they may contact you within the 28-day period. If you receive no contact, you can proceed to commission after 28 days.
Commission and Test
Commission the system per MCS requirements. Test the inverter’s anti-islanding (loss of mains) protection and record the results. The DNO may request to inspect the commissioning records at any time — keep them for at least 2 years.
Send Commissioning Confirmation
After commissioning, send a completed G98 commissioning notification to the DNO within 28 days of energisation. This is a separate submission from the pre-installation notification. Failure to submit this is a common compliance gap.
G98 Common Mistakes
| Mistake | Consequence |
|---|---|
| Submitting the notification fewer than 28 days before commissioning | System cannot be legally energised until 28 days after notification |
| Forgetting the post-commissioning notification | Technical non-compliance; can affect SEG registration |
| Not checking for existing generation at the premises | Combined output may exceed G98 threshold — requires G99 |
| Using incorrect MPAN | DNO cannot match the application to the premises |
The G99 Process: Formal Application
G99 is a formal application process. The DNO must review and accept the application before the system can be energised.
Timeline
| Stage | Timeframe |
|---|---|
| DNO initial review | 5–10 working days |
| DNO technical assessment | Up to 45 working days total |
| DNO acceptance or conditions issued | Within 45 working days |
| System energisation | After written acceptance received |
If the DNO does not respond within 45 working days, the application is deemed accepted and the system may be energised. Keep evidence of the submission date and the 45-day deadline.
What a G99 Application Requires
Application Form
The DNO’s G99 application form. Includes: installation address, MPAN, system description, generating unit type (inverter-based PV), rated AC output, and whether export limitation is in place.
Single-Line Diagram
An electrical single-line diagram showing the PV array, inverter(s), generation meter, import/export meter, main fuse, isolation switches, and the grid connection point. Must include all protection relay functions and their settings.
Equipment Specifications
Manufacturer data sheets and type test certificates for inverters, protection relays, and generation meters. The inverter must be type-tested to BS EN 62116 (anti-islanding) and BS EN 61000-3-2 (harmonic emissions) as a minimum.
Protection Relay Settings Schedule
A completed protection settings schedule showing the under/over voltage and under/over frequency trip settings for the inverter. G99 specifies default settings; some DNOs require tighter settings for specific network conditions. The DNO may issue amended settings as a condition of acceptance.
Export Limitation Details (if applicable)
If the system uses export limiting (to stay below a DNO-imposed export cap), provide details of the export limitation device and its settings. Export limiting is increasingly used as a commercial condition for G99 connections where the network has limited export capacity.
What the DNO Assesses
The DNO’s technical review focuses on:
- Whether the local network can absorb the additional export capacity
- Whether the protection settings meet G99 requirements
- Whether there are any power quality concerns (harmonics, voltage rise)
- Compliance with any local network standard conditions
The DNO can:
- Accept the application unconditionally
- Accept with conditions (e.g., reduced export limit, specific protection settings)
- Reject the application (rare; usually only where the network genuinely cannot accommodate the connection)
Protection Settings: Loss of Mains
Both G98 and G99 require inverters to have loss of mains (LoM) protection — the function that disconnects the inverter from the grid if the grid fails, preventing the inverter from islanding on a de-energised section of the network.
Standard G98/G99 protection settings (default):
| Function | Setting |
|---|---|
| Under Voltage | 0.87 pu (200V) — trip within 2.5s |
| Over Voltage Stage 1 | 1.14 pu (264V) — trip within 1s |
| Over Voltage Stage 2 | 1.19 pu (273V) — trip within 0.5s |
| Under Frequency | 47 Hz — trip within 20 cycles |
| Over Frequency | 52 Hz — trip within 0.5s |
| Rate of Change of Frequency (RoCoF) | 1 Hz/s — trip within 500ms |
Most UK-certified grid-tied inverters (Fronius, SMA, SolarEdge, Enphase, etc.) are pre-configured to these settings. You should verify the protection settings on the inverter’s commissioning screen before energisation and record them in the commissioning documentation.
Check the DNO’s Network-Specific Conditions
Some DNOs — particularly in areas with high renewable penetration or sensitive network topologies — require tighter LoM settings than the G98/G99 defaults. UKPN, for example, has published supplementary standard conditions for certain network areas. Check the DNO’s website for any applicable standard conditions before finalising protection settings.
Smart Export Guarantee: Connecting to SEG
The Smart Export Guarantee (SEG) is the mechanism for UK solar export payments, replacing the Feed-in Tariff (FiT) scheme which closed to new applicants in March 2019. SEG requires:
- The system to be MCS-certified (or ROOFIT equivalent for larger installations)
- A smart export meter capable of half-hourly export readings (almost all smart meters installed in the UK since 2016 are capable)
- Registration with a SEG-licensed electricity supplier
G98/G99 compliance is a prerequisite for SEG registration — a system cannot be SEG-registered if it has not been correctly notified to or accepted by the DNO.
Current SEG rates (April 2026, indicative):
| Supplier | Rate |
|---|---|
| Octopus Energy | 15p/kWh (Intelligent Octopus) |
| E.ON Next | 5.6p/kWh |
| British Gas | 5.5p/kWh |
| EDF Energy | 5p/kWh |
| OVO Energy | 4p/kWh |
Rates change frequently. Check the Ofgem SEG register for current offerings.
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MCS Certification: The Practical Requirement
While MCS certification is technically separate from G98/G99, the two are inseparable in practice for UK residential and small commercial solar:
- MCS is required for SEG registration
- MCS is required for many building warranties and mortgage lender requirements
- MCS provides the consumer with a 5-year installation workmanship warranty via the MCS Guarantee
MCS for installers: Solar installers must be certified under MCS 001 (Products) and MCS 012 (Solar PV Installation Standard). The certification is held by the installation company, not the individual. Certification is obtained through an MCS-approved certification body (such as NAPIT, NICEIC, or RECC).
MCS for products: Solar panels and inverters must be MCS 001-certified products for the installation to qualify for the MCS certificate. The MCS product directory lists all currently certified products.
Frequently Asked Questions
What is the difference between G98 and G99 for battery storage?
Battery storage inverters and hybrid inverters are treated as generating units under G98/G99. A battery inverter with AC output up to 16A per phase follows G98. Larger battery systems, or battery additions that push a premises above the G98 threshold, require G99. DC-coupled batteries connected behind an existing inverter may fall under G100 rather than G98/G99 — check the ENA guidance for the specific configuration.
What if the DNO asks for export limitation as a condition of G99 acceptance?
Export limitation (also called zero export or export capping) is a common DNO condition in constrained network areas. The DNO specifies a maximum export level in kW, and the inverter (or a dedicated export limiting device) ensures exports never exceed that level. Most modern inverters support export limiting natively. If the DNO specifies export limitation, you need a dedicated generation meter and the export limiting function enabled and tested at commissioning.
Do I need a separate generation meter for G98?
G98 does not require a separate generation meter — the system can use the smart export meter for both import/export measurement. However, if the customer wants SEG payments, a smart export meter capable of half-hourly readings must be in place. For G99, a separate generation meter is typically required.
Can I connect solar PV to a three-phase supply under G98?
Yes. For a three-phase property, the G98 threshold is 16A per phase — meaning a total output of up to 11.04 kW (16 × 230 × 3) can be G98-notified. Three-phase inverters for commercial rooftop systems under 11 kW commonly use G98 notification. Above 11 kW on three-phase, G99 applies.
What happens if I energise a system without completing the G98 notification?
Connecting a generating unit to the distribution network without a valid G98 notification (or G99 acceptance) is a breach of the ESQCR and the distribution licence conditions. The DNO can require disconnection. Insurance on the property and the installation may also be void if the grid connection was not properly notified. Always submit G98 notification before commissioning.
