G99 Connections Explained: The Essential Guide for UK Solar and Battery Installations

What Is a G99 Connection in the UK Solar Industry?

A G99 connection refers to the set of regulations and procedures governing the connection of generation equipment—such as solar PV systems, battery storage, wind turbines, or combined heat and power units—to the UK electricity distribution network. The term “G99” comes from Engineering Recommendation G99, a standard published by the Energy Networks Association (ENA) that replaced the earlier G59 standard in 2019.

G99 applies to all generation systems with a capacity greater than 16A per phase (roughly 3.68kW per phase), which typically includes:

• Larger domestic solar PV arrays
• Commercial and industrial solar installations
• Battery storage systems above the threshold
• Hybrid systems combining multiple technologies

If your system is below this threshold, the simpler G98 process applies. For most modern homes and businesses seeking to maximise solar output or install substantial battery storage, G99 is the relevant standard.

Why Are G99 Connections Needed for Solar and Battery Systems?

G99 connections are essential to protect both the UK’s electricity grid and the people who use it. As more distributed generation comes online, the risk of destabilising the grid increases if connections aren’t properly managed. G99 ensures that:

• Grid stability is maintained: Large generators can affect local voltage and frequency. G99-compliant systems must include features to disconnect or adjust output if grid parameters move outside safe limits.
• Safety is prioritised: In the event of a power cut, G99 ensures that generators don’t continue feeding electricity into the grid, protecting engineers working on the lines.
• Fair access is provided: The process helps distribution network operators (DNOs) assess whether the local network can accommodate new generation and, if not, what upgrades or restrictions are needed.

Without G99, the rapid expansion of solar and battery storage could lead to power quality issues, safety hazards, and even blackouts. The regulation is a cornerstone of the UK’s transition to a smarter, greener grid.

How Does the G99 Application Process Work?

The G99 process is more involved than the simpler G98 notification. Here’s a step-by-step overview of how it works:

1. Preliminary Assessment: Your installer (such as Atlantic Renewables) will assess your site, system size, and local grid capacity to determine if a G99 application is required.
2. Application Submission: A detailed application is submitted to your local DNO, including system specifications, single-line diagrams, and protection settings.
3. DNO Review: The DNO reviews the application, often conducting a network study to assess the impact of the new generation on their infrastructure.
4. Offer and Acceptance: The DNO issues a connection offer, detailing any required network upgrades, costs, and timescales. You must formally accept this offer before proceeding.
5. Installation and Testing: Once permission is granted, the system can be installed. G99 requires specific commissioning tests to demonstrate compliance.
6. Final Notification: After successful testing, a commissioning report is sent to the DNO, who then grants final approval for ongoing operation.

This process can take several weeks to months, especially for larger or more complex projects. Atlantic Renewables’ team of experts can manage the entire process, ensuring compliance and minimising delays.

What Systems Require a G99 Connection?

G99 applies to any generation system above 16A per phase, which typically includes:

• Domestic solar PV arrays over 3.68kW per phase
• Commercial solar installations (often 10kW, 20kW, or larger)
• Battery storage systems exceeding the threshold
• Wind, hydro, or CHP systems above the limit

If you’re planning to install a 10kW or 20kW solar system with battery storage—common sizes for businesses and larger homes—you’ll almost certainly need to follow theG99 process . Atlantic Renewables can advise on the specific requirements for your project and handle all liaison with your DNO.

What Are the Key Technical Requirements of G99?

G99 sets out a range of technical requirements to ensure safe and stable operation, including:

• Loss of Mains Protection: Systems must disconnect from the grid if they detect a loss of supply, preventing “islanding.”
• Voltage and Frequency Limits: Generators must monitor grid conditions and disconnect if voltage or frequency moves outside defined limits.
• Anti-Islanding Measures: Inverters and other equipment must be certified to G99 standards, ensuring they behave predictably in abnormal conditions.
• Commissioning Tests: Installers must carry out and document specific tests to prove compliance before the system is allowed to operate continuously.

Meeting these requirements is essential not only for grid safety but also for insurance, warranties, and eligibility for export payments.

How Can Installers and Customers Ensure a Smooth G99 Process?

The G99 process can seem daunting, but with the right expertise, it’s entirely manageable. Here’s how to ensure a smooth experience:

• Choose an experienced installer: Atlantic Renewables has extensive experience navigating G99 for both domestic and commercial clients.
• Plan ahead: Start the application process early, as DNO approval can take several weeks or even months.
• Provide accurate information: Detailed system specifications and diagrams are essential for a successful application.
• Communicate with your DNO: Prompt responses to queries and a proactive approach can help avoid unnecessary delays.

Our engineers at Atlantic Renewables handle the entire G99 process for you, from initial assessment to final commissioning, ensuring your solar or battery project is compliant and connected as quickly as possible.

Why G99 Connections Matter for the Future of Solar in the UK

As the UK accelerates its transition to net zero, the number and size of distributed generation systems will only increase. G99 is a critical enabler of this transition, providing a framework that balances innovation with safety and reliability. By understanding and embracing G99, installers and customers alike can play their part in building a cleaner, smarter, and more resilient energy system.

Get in touch

Thinking of installing a larger solar PV or battery storage system? Need expert help with your G99 application? Contact Atlantic Renewables today—our team of experts will guide you through every step of the process, ensuring your system is safe, compliant, and ready to power your future. Call us on 0161 207 4044 and let us help you take the next step towards clean, reliable energy.