What Is G99 Grid Code? A UK Guide to G98 and G99
What is G99 grid code, and does your solar or battery project need it? PTOEdge helps UK installers answer that question quickly. So, speak to our design team today and get your DNO paperwork moving.
G99 is the engineering standard for larger generation connections to the UK network. Meanwhile, G98 covers small systems. This guide explains what is G99 grid code in plain English. Moreover, it covers the G98 vs G99 split, application steps, timelines and the paperwork you receive. Finally, you will see how our UK solar design services support each stage.
Table of Contents
What Is G99 Grid Code?
What is G99 grid code in simple terms? It is the Energy Networks Association rule set for connecting generation above 16 A per phase to the UK distribution network. In other words, any larger solar array, battery or hybrid system must follow it. The distribution network operator, or DNO, reviews your design before you energise the system.
The standard sits alongside G98, which covers smaller installations. Together, they replaced the older G83 and G59 rules in 2019. Because these rules protect network stability, every installer needs to understand them. This Wikipedia page on distribution network operators explains the wider role of a DNO.
Who Publishes G99 and Why It Matters
The Energy Networks Association, known as the ENA, publishes both documents for network companies. Therefore, the rules apply across Great Britain in a consistent way. Each DNO then adds its own forms and portals. As a result, the process feels similar in London and in the Scottish Highlands.
What Is G99 Grid Code Compared With G98?
G98 is a connect-and-notify route for small systems. G99, however, needs approval before you connect. This difference shapes your programme, your cost and your customer’s expectations. The table below shows the G98 vs G99 split at a glance.
| Feature | G98 | G99 |
|---|---|---|
| System size | Up to 16 A per phase (about 3.68 kW single-phase) | Above 16 A per phase |
| Process | Install first, then notify within 28 days | Apply and wait for DNO approval |
| Equipment | Type-tested units on the ENA register | Type-tested units or full compliance evidence |
| Timeline | Notification after commissioning | Quotation within 45 working days for low voltage |
G98 vs G99: How the 16A Per Phase Limit Works
To understand what is G99 grid code, start with the 16 A rule. On a single-phase supply, that equals about 3.68 kW. On a three-phase supply, the same rule allows roughly 11.04 kW in total. However, the limit covers everything at the premises, not each device. Therefore, you must add solar inverters and battery inverters together.
This is where many jobs tip over. For example, a 4 kW single-phase inverter works out at about 17.4 A, so it needs G99. Likewise, a home with 2 kW of existing panels that adds another 2 kW crosses the line too.
G98 up to 3.68 kW
A 3.68 kW single-phase inverter normally follows G98, so you notify the DNO after commissioning. Our DNO application guide shows each step.
G99 above 3.68 kW
A 4 kW inverter exceeds 16 A per phase, so G99 applies and you need approval first. Therefore, plan the extra weeks into your programme.
Solar plus battery
A 3.68 kW solar inverter with a 3 kW battery inverter totals 6.68 kW. As a result, the property moves into G99 even though each unit looks small.
What Is G99 Grid Code for Solar and Battery Projects?
What is G99 grid code in practice for solar and storage? It means you design the whole system around network limits from day one. Battery storage that exports to the grid counts as generation. Similarly, hybrid inverters add to your per-phase total. So, an early capacity check saves costly redesigns.
Commercial rooftops face the same rule at a larger scale. Larger arrays often need extra studies and longer review times. For that reason, our guide to commercial solar system design in the UK explains how layout and inverter choices affect the connection route.
Export limitation can also help. A G100 scheme caps export, and some DNOs accept it so a project can follow a simpler route. However, the DNO makes the final decision, so ask before you design around it.
G98 Application: Connect First, Then Notify
A G98 application is really a notification. You install first, then tell the DNO within 28 days of commissioning. Your inverter should appear on the ENA Type Test Register, because type-tested equipment allows this simple route. Recent updates also moved submissions onto the ENA Connect Direct platform.
Follow these steps for a smooth G98 application:
- First, confirm your total capacity stays within 16 A per phase.
- Next, check that your inverter model has type-test evidence.
- Then install and commission the system safely.
- After that, submit the notification within 28 days.
- Finally, keep the confirmation with your handover pack.
For letters, forms and approvals in more detail, read our full DNO application walkthrough.
G99 Application Steps From Design to Approval
A G99 application takes more planning than G98. Because you need approval before you connect, preparation matters. The steps below keep your project on track.
- First, define the system size, inverter ratings and any battery storage.
- Next, identify the DNO for the site address.
- Then complete the correct G99 form with equipment data.
- After that, attach layouts and single-line diagrams.
- Meanwhile, respond quickly to any DNO questions.
- Finally, accept the offer, install, commission and notify.
Clear drawings speed up the review. Our overview of solar plan set requirements shows what a UK-ready drawing pack includes.
What Is G99 Grid Code Approval Timing?
What is G99 grid code approval timing in real life? Under Ofgem’s guaranteed standards, a DNO has 45 working days to issue a low-voltage generation quotation once it holds complete information. Simple domestic cases often return sooner. Meanwhile, larger or complex projects take longer. Because the clock starts with full details, a complete submission matters.
G99 Application Perth: Scottish Network Considerations
A G99 application Perth installers submit goes to the local network operator. Perth in Scotland sits within the SSEN distribution area, so SSEN’s forms and portal normally apply. However, you should always confirm the operator for each postcode before you submit.
If you ask what is G99 grid code in Scotland, the answer matches England and Wales. Remote sites, though, may face weaker network capacity. Consequently, early enquiries help you avoid delays. In addition, the same rules apply nationwide, so your design logic stays consistent.
What Is G99 Grid Code Documentation? Your G99 Certificate Explained
Strictly speaking, no single document carries the name G99 certificate. Instead, installers use the term for the approval pack. This pack usually includes the DNO’s approval or connection offer, your commissioning records and, for larger projects, a final operational notification.
Therefore, ask your DNO which forms apply to your project. Keep every record, because customers, lenders and inspectors often request them. In practice, what is G99 grid code documentation worth? It proves your system connects legally and safely.
Why Design Quality Matters When You Learn What Is G99 Grid Code
Anyone learning what is G99 grid code soon sees that design drives approval. PTOEdge prepares accurate layouts, inverter schedules and single-line diagrams for UK solar projects. As a result, DNO reviewers see consistent data. Our team also checks system size against the 16 A per phase limit before drawings finish.
Consequently, you avoid choosing the wrong route. To see how we support installers from concept to approval, explore our UK solar design and permitting services. Besides, a clear design builds customer trust because it shows a compliant, professional process.
Common G98 and G99 Mistakes to Avoid
Even experienced teams slip on these points. Fortunately, each one is easy to prevent.
Ignoring batteries
Some teams count only solar. However, storage adds to the total, so check the combined figure.
Installing before approval
G99 needs approval first. Otherwise, you risk costly changes later.
Missing equipment evidence
Without type-test details, the DNO may ask for more data. As a result, the application slows down.
Wrong DNO
Network areas differ by address. Therefore, confirm the operator before you submit anything.
Need help with a G98 or G99 project?
Share your system size and postcode. Then PTOEdge will advise on the right route and prepare a clear design pack.
FAQs on What Is G99 Grid Code
What is G99 grid code?
It is the ENA standard for generation above 16 A per phase. Therefore, larger solar and battery systems need DNO approval first.
What is the difference between G98 and G99?
G98 means connect, then notify within 28 days. However, G99 needs approval before you connect.
Do I need a G99 application in Perth?
Yes, if your system exceeds 16 A per phase. Also, confirm the local operator before you submit.
Is there an official G99 certificate?
Not as one single document. Instead, you receive approval and commissioning records.
How long does a G99 application take?
A DNO has 45 working days for a low-voltage quotation. However, simple cases can return faster.
Final Thoughts on What Is G99 Grid Code
Knowing what is G99 grid code helps you plan faster, safer UK solar projects. Furthermore, you now understand the 16 A per phase rule, the G98 notification route and the G99 approval steps. So, choose the correct route early and keep your documents tidy.
Next, speak with PTOEdge about your upcoming UK project. Our team will review your system, confirm the route and prepare the design. Besides, you can contact our team directly or explore the PTOEdge homepage for solar design, permitting and plan set support.