DNO Grid Connection Guide: G98 vs G99 Applications

Every commercial solar installation must be connected to the electricity grid with approval from your local Distribution Network Operator. This guide explains the application process, timelines, costs, and what happens when reinforcement is required.

What Is DNO Approval and Why Do You Need It?

The Distribution Network Operator (DNO) is the company responsible for maintaining the local electricity network in your area. When you install a solar panel system that generates electricity, that power can flow back into the local grid. The DNO must approve this connection to ensure the network remains safe, stable, and within its operating limits. Without DNO approval, connecting a generating system to the grid is illegal and could create safety hazards for network engineers and other users.

The approval process exists because the electricity grid was originally designed to carry power in one direction, from large power stations to consumers. Distributed generation from solar panels reverses this flow at the local level, which can cause voltage rise, thermal overloading, and protection coordination issues if not properly managed. The DNO assessment ensures your solar system can be safely integrated without adversely affecting other users connected to the same part of the network.

The specific approval process depends on the size of your solar system and is governed by the Engineering Recommendation G98 for smaller systems and G99 for larger systems. Both standards are published by the Energy Networks Association and apply uniformly across all DNO regions in Great Britain.

G98: For Smaller Systems

The G98 standard applies to generating systems with an export capacity of up to 16 amps per phase. In practical terms, this means up to 3.68 kW on a single-phase electricity supply or up to 11.04 kW on a three-phase supply. G98 is a notification-only process, meaning the installer simply informs the DNO that the system has been connected. There is no need to wait for approval before installation or commissioning.

The G98 process is straightforward. The installer submits a notification form to the DNO within 28 days of commissioning, providing details of the installation including the inverter type, rated capacity, and protection settings. The DNO does not need to approve the connection in advance, and there is no application fee. This makes G98 connections quick and cost-effective.

However, very few commercial solar installations fall within the G98 threshold. A 3.68 kW single-phase system would consist of just 8 to 10 solar panels, which is far too small for most business premises. Even the three-phase limit of 11.04 kW represents only 24 to 28 panels. The vast majority of commercial installations require G99 approval, which we cover in detail below.

G99: For Commercial Solar Systems

The G99 standard applies to all generating systems with an export capacity exceeding 16 amps per phase. This covers virtually every commercial solar installation in the UK, from a 15 kW system on a small office building to a multi-megawatt array on a distribution centre. Unlike G98, the G99 process requires formal application, technical assessment by the DNO, and written approval before the system can be connected to the grid.

The G99 application process is divided into several clearly defined stages. Understanding each stage helps you plan your project timeline and anticipate potential costs or delays. Installers manage this entire process on behalf of their clients, but transparency about what is involved helps you make informed decisions about your project.

The G99 Application Process

Grid Connection Costs

The cost of connecting a commercial solar system to the grid varies significantly depending on the capacity of the local network and whether any reinforcement is required. For many installations, the grid connection cost is modest. However, in areas with constrained network capacity, reinforcement costs can be substantial. Understanding these potential costs early in the project helps you budget accurately and evaluate alternatives such as export limitation.

A good installer carries out a preliminary network capacity check before submitting the formal G99 application, which gives you an early indication of whether reinforcement is likely to be required. This avoids surprises later in the process and allows alternatives to be explored such as export limitation or phased installation if the network is heavily constrained. For a detailed breakdown of all project costs, see our commercial solar cost guide.

Export Limitation as an Alternative

Export limitation is an increasingly popular solution for commercial solar installations where the local grid capacity is constrained. Rather than paying for expensive network reinforcement, an export limiting device is installed that automatically curtails the system output when the power being exported to the grid exceeds a set threshold.

For example, a business might install a 150 kW solar system but agree to limit grid export to 50 kW. During the middle of the day when the building is consuming 80 kW and the panels are generating 150 kW, only 70 kW would be exported, well within the 50 kW limit would not apply because the building is already consuming most of the generation. Export limitation typically results in less than 3 to 5 per cent of annual generation being curtailed, making it a cost-effective compromise that avoids tens of thousands of pounds in reinforcement costs.

All six UK DNOs accept export limitation as part of the G99 connection process. The export limit is specified in the connection agreement and enforced by a certified relay or energy management system. Export-limiting systems track export in real time, ensuring your system remains compliant at all times.

Which DNO Serves Your Region?

Great Britain is divided into six DNO licence areas, each operated by a different company. Your DNO is determined by the geographical location of your property and cannot be changed. The DNO is not the same as your electricity supplier, which is the company you pay your bills to. Below is a summary of each DNO and the regions they serve.

If you are unsure which DNO serves your area, you can check using the postcode lookup tool on the Energy Networks Association website. Alternatively, your installer can identify your DNO from your postcode and handle the communications on your behalf. Experienced installers work regularly with the DNOs, which helps the application process run smoothly.

How an installer manages the DNO application for you

The DNO application process is one of the most technically demanding aspects of a commercial solar project. Incorrect applications, incomplete documentation, or poorly specified protection settings can result in rejections, delays, and additional costs. An experienced installer will have submitted many G99 applications across the DNO regions and understands the specific requirements and preferences of each operator.

A good installer handles every step of the process, from the initial network capacity assessment through to commissioning notification. This includes preparing single line diagrams, specifying protection relay settings, coordinating with DNO engineers during the assessment phase, and managing any issues that arise. Check that the cost of the DNO application is included in the project price, so there are no hidden charges.

For larger projects requiring three-phase solar systems, the G99 application is particularly important as it determines the connection arrangements, protection requirements, and any export limitations that apply. Getting this right from the start ensures a smooth installation and avoids costly changes during commissioning.

Get Your Free Grid Assessment

Ask the installer to check your local grid capacity and advise on the best connection strategy for your site.

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What should be included

DNO applications, grid assessments and commissioning notifications should all be included in the installation service — check the quote so there are no hidden costs and no paperwork left with you.

DNO Grid Connection FAQs

Highlights

• Roof Assessment Guide
• /commercial-roof-assessment
• Installation Process
• /commercial-solar-installation-process
• Three-Phase Solar
• /three-phase-solar-systems
• Solar Monitoring
• /commercial-solar-monitoring
• Installation Costs
• /commercial-solar-installation-costs