When you’re considering solar panels for your home, you’ll probably come across terms like G98, G99, DNO approval and DNO letter. While these may sound complicated, they’re simply part of the process that ensures your solar PV system connects safely to the electricity grid.
At SolarTherm UK, we help homeowners throughout Essex, Kent, Suffolk, Hertfordshire and the wider South East and East Anglia navigate every stage of the installation process, including dealing directly with your local Distribution Network Operator (DNO).
This guide explains the difference between G98 and G99, what they mean for your installation and whether they’ll affect your project timeline.
What Does DNO Mean?
Before understanding G98 and G99, it’s important to understand the meaning of DNO. A Distribution Network Operator (DNO) owns and maintains the local electricity network that delivers power to your home.
Unlike your energy supplier, who sends your bills, your DNO is responsible for ensuring the local electricity network can safely handle electricity being exported from solar PV systems.
Whenever a new solar installation is connected to the grid, your installer must follow the relevant Engineering Recommendation issued by the Energy Networks Association. For most homeowners, this usually means either a G98 notification or a G99 application. The correct route depends on the size of your solar PV system.
What is G98?
G98 is the simpler notification process. It applies to smaller domestic solar systems where the inverter capacity is up to 3.68kW per phase. Rather than requesting permission before installation, your installer can usually install the system first and then notify the DNO afterwards. This makes installation faster and reduces paperwork for homeowners.
What is G99?
G99 applies when a solar installation is capable of exporting more electricity than the G98 limit allows. This generally means larger solar arrays, more powerful inverters, battery storage systems and three phase installations. Unlike G98, permission must be granted before installation begins. The DNO assess whether the local electricity network can safely accommodate the additional generation. Approval times can vary depending on workload and network complexity.
G98 v G99: What’s the Difference?
| Feature | G98 | G99 |
| Maximum inverter size | Up to 3.68kW | Above 3.68kW |
| Permission required before installation? | No | Yes |
| DNO involvement | Notification after installation | Approval before installation |
| Typical property | Standard homes | Larger homes or higher-output systems |
| Installation timeline | Short | 6-12 weeks in some cases |
The choice isn’t based purely on the number of solar panels – it depends on the maximum inverter output being connected to the electricity network. An experienced installer will calculate this during your survey.
Why Can’t Every Solar System Use G98?
Many homeowners ask why installers don’t simply register every installation under G98. The answer is grid protection. Electricity networks were originally designed for homes consuming power – not exporting significant amounts into the grid.
Larger systems have a greater impact on local voltage levels and network stability, so the DNO needs to assess whether the infrastructure can support additional exported electricity safely to protect your property, neighbouring homes, local substations and the wider electricity network.
Can Battery Storage Affect G98 or G99?
Yes. Modern battery storage systems often increase the inverter capacity of an installation. For example, even if your solar array itself would qualify under G98, adding a larger hybrid inverter or battery may mean the installation falls under G99 instead.
This is one reason it’s important to design the complete system before submitting the DNO application. At SolarTherm UK, we assess the entire system – including future expansion plans – to ensure the correct application is made from the outset.
Does G99 Mean I Need Solar Planning Permission?
No, this is a common misconception. Solar planning permission and G99 approval are completely different. Planning permission relates to whether your local authority allows the physical installation. G99 relates to connecting your system safely to the electricity network.
Most homes benefit from Permitted Development Rights, meaning planning permission isn’t required for roof mounted solar PV systems. However, you may need planning permission if your property is listed, within a conservation area, subject to planning restrictions or installing a large ground mounted system. Your installer should advise on both planning requirements and DNO approval separately.
What Is a DNO Letter?
A DNO letter is simply written confirmation from your Distribution Network Operator. Depending on your project, it may include:
- Confirmation that your G99 application has been approved
- Export limitations
- Network upgrade requirements
- Permission to connect
- Technical conditions
Most homeowners never need to deal with this paperwork themselves because SolarTherm UK manages the entire application process on your behalf.
Will G99 Delay My Installation?
Sometimes, but not always. Straightforward applications may be approved within a few weeks, while more complex applications can take longer if the DNO needs to assess local network capacity. Submitting a complete, accurate application significantly reduces delays. Over the last 16+ years, SolarTherm UK has completed thousands of DNO applications on behalf of customers, working closely with both the customer and the DNO to ensure applications are completed correctly the first time.
Why Professional DNO Management Matters
Incorrect G98 or G99 applications can delay installations and create unnecessary costs. Choosing an experienced installer means:
- Accurate system design
- Correct inverter sizing
- Proper DNO submissions
- Compliance with current Engineering Recommendations
- A smoother installation process
SolarTherm UK manages every stage – from your initial survey through to final grid notification – so you don’t have to navigate technical regulations yourself.
Why Homeowners Across the South East Choose SolarTherm UK
With over 16 years of experience designing and installing residential solar PV systems, SolarTherm UK understands both the technical requirements and the practical considerations involved in connecting your home to the electricity network.
Our qualified in house engineers work to current industry standards and stay up to date with changes to DNO processes, Engineering Recommendations and UK installation best practices.
Whether you’re installing a modest rooftop system of a larger solar and battery solution, we’ll determine whether your project falls under G98 or G99 and manage the application on your behalf.
Our expertise supports homeowners across Essex, Kent, Suffolk, Hertfordshire and the surrounding South East and East Anglia, helping ensure installations are compliant, efficient, reliable and completed with minimal disruption.
Contact SolarTherm UK today for a free, no obligation quote and design, tailored to your property, usage and future energy needs. No hard sell, just honest, expert advice – and the time you need to make an informed decision.
Your home. Your energy. Your future.
Frequently Asked Questions
G98 is for smaller solar installations up to 3.68kW inverter output and only requires the DNO to be notified after installation. G99 is for larger systems and requires DNO approval before installation begins.
A Distribution Network Operator (DNO) manages the local electricity network and ensures new solar installations can safely connect to the grid.
For G99 installations, yes. Your installer will usually receive the approval documents and manage the process on your behalf before providing confirmation to you.
No. G99 concerns grid connection, whereas solar planning permission relates to local planning rules. Most domestic rooftop solar installations fall under Permitted Development Rights.
Yes. Larger hybrid inverters and battery systems can increase the system’s export capability, meaning a G99 application may be required even if the solar array itself appears relatively small.
Your installer will calculate the inverter output and determine which Engineering Recommendation applies before installation begins.
