What Is a DNO?

DNO Approval Explained for Home Solar Panels

Installing solar panels is one of the best ways to reduce your electricity bills and become less reliant on the grid. However, before your new solar PV system can begin exporting electricity, it may need approval from your local Distribution Network Operator (DNO).

Many homeowners hear terms like G98, G99, G100, DNO letter and export limitation, but aren’t sure what they actually mean. Understanding these regulations helps you make informed decisions and ensures your installation complies with UK electrical standards.

At SolarTherm UK, we manage the entire DNO application process on behalf of our customers across Essex, Kent, Suffolk, Hertfordshire and the wider South East and East Anglia, making the journey from quotation to installation as smooth as possible.

What Does DNO Mean?

One of the most common questions homeowners ask is:

“What is the meaning of DNO?”

A Distribution Network Operator (DNO) is the company responsible for maintaining and operating the electricity distribution network in your local area. They own the cables, substations and infrastructure that deliver electricity to homes and businesses.

Your electricity supplier sells your energy, while your DNO ensures the local electricity network remains safe and reliable. When you install solar panels, your system can export surplus electricity to the grid. The DNO needs to ensure that your local network can safely accept this additional generation without affecting neighbouring properties.

Why Does Solar Need DNO Approval?

Solar PV systems don’t simply generate electricity for your home. When your panels produce more electricity than you’re using, the surplus energy is exported to the National Grid. If many homes export large amounts of electricity at the same time, local electricity networks can become overloaded.

The DNO approval process helps to:

• Protect the local electricity network
• Prevent voltage fluctuations
• Maintain grid stability
• Ensure electrical safety
• Support future renewable energy growth

For most homeowners, this process is handled entirely by their installer. At SolarTherm UK, we submit all necessary applications, communicate with the DNO and ensure your installation complies with current engineering recommendations.

What Is a DNO Letter?

You may hear installers mention a DNO letter during the quotation process. A DNO letter is simply written confirmation from your Distribution Network Operator regarding your solar installation.

Depending on the project, this could include:

• Confirmation that your installation has been registered
• Approval for connection
• Permission to export above standard limits
• Confirmation of any export restrictions
• Technical requirements before installation

Most homeowners never need to deal directly with the DNO because their installer manages the process from start to finish.

Understanding G98

G98 is the simplest connection process for domestic solar installations. It applies to smaller generating systems that fall within specific export limits. Rather than asking for permission before installation, qualifying G98 systems are generally installed first and then registered with the DNO afterwards.

Typical characteristics include:

• Smaller residential systems
• Straightforward notification process
• Faster approvals
• Lower administrative requirements

Many standard domestic solar installations fall under G98, although battery storage and larger inverter sizes can change which application is required.

Understanding G99

G99 applies to larger or more complex solar installations. Unlike G98, approval must usually be obtained before installation begins. A G99 application allows the DNO to assess whether the local electricity network can safely accommodate the proposed generation capacity.

This process may include:

• Network studies
• Export assessments
• Connection conditions
• Export limitations where necessary

Although the application process can take longer than G98, it allows homeowners to install larger systems that may better meet their long term energy requirements.

What Is G100?

G100 is often misunderstood but can be extremely useful. Rather than reducing the size of your solar installation, G100 allows an installer to electronically limit how much electricity is exported to the grid. This means you may be able to install a larger solar array while ensuring exports stay within the level approved by the DNO. A G100 compliant export limitation system continuously monitors electricity flowing to the grid and automatically reduces exports whenever necessary.

This allows homeowners to:

• Install more solar panels
• Generate more electricity for their own use
• Charge larger battery storage systems
• Future proof their property
• Remain compliant with DNO requirements

What Are Export Limitations?

An export limitation controls the maximum amount of electricity your property can send back to the grid. Rather than limiting how much electricity your solar panels produce, it only limits exported energy. Any electricity used within your home isn’t affected.

For example, if your home is using 5kW while your panels produce 8kW, only 3kW is exported. If your DNO export limit is 3kW, the system operates normally. If exports would exceed that level, the export limitation system automatically adjusts inverter output.

For many homeowners, export limitation offers the best balance between maximising self-consumption and complying with grid requirements.

Understanding Inverter Capacity Limits

One area that often causes confusion is inverter sizing. Your solar panels and inverter are closely linked, but they perform different jobs. Solar panels generate DC (direct current) electricity and the inverter converts it into usable AC (alternating current) electricity for your home.

The size of your inverter plays a major role in determining whether your installation falls under G98 or G99 requirements. Larger inverter capacities generally require additional DNO assessment because they can potentially export more electricity onto the network.

An experienced installer will design your system to achieve the best balance between:

• Roof size
• Household electricity demand
• Battery storage
• Future EV charging
• Heat pump compatibility
• DNO requirements

At SolarTherm UK, every system is individually designed rather than relying on standard package sizes.

Can Battery Storage Affect DNO Approval?

Yes. Battery storage systems can influence which application is required, particularly where batteries can export electricity back to the grid. Hybrid inverters, AC coupled batteries and larger battery systems may all affect the overall export capability of the installation.

This is why a professional system design is essential before installation begins. Our technical team assesses the complete system – including solar panels, inverter and battery storage – to ensure full compliance before any work starts.

Do I Need to Apply to the DNO Myself?

In almost every residential installation, the answer is no. A reputable MCS certified installer should:

• Design your system correctly
• Identify the correct application type
• Complete all paperwork
• Submit applications
• Liaise with the DNO
• Obtain approvals where required
• Provide confirmation once complete

This removes the complexity for homeowners and ensures everything complies with UK regulations.

Why Professional System Design Matters

Choosing the right installer is about much more than fitting solar panels. Incorrect inverter sizing, overlooked export limits or incomplete can delay installations or require expensive modifications later.

At SolarTherm UK, every project includes:

• Detailed site survey
• Bespoke system design
• DNO assessment where required
• MCS compliant installation
• NICEIC certified electrical work
• Full commissioning and testing
• Ongoing customer support

Our experienced team has delivered residential solar installations across Essex, Kent, Suffolk, Hertfordshire and the wider South East and East Anglia, helping homeowners navigate planning requirements, DNO approvals and electrical regulations with confidence.

Whether you’re installing a small rooftop system or a larger battery backed solution, we’ll ensure your project is designed for maximum performance while remaining fully compliant.

Why Choose SolarTherm UK?

When investing in solar, experience matters. SolarTherm UK combines technical expertise with a customer first approach, ensuring every installation is designed around your home’s energy needs and future plans.

As an MCS certified contractor, NICEIC approved installation and EPVS Gold Standard member, we work to recognised industry standards and stay up to date with the latest engineering recommendations and regulatory requirements. Our in house teams manage everything from initial design through to DNO applications, commissioning and aftercare, giving homeowners complete peace of mind.

Whether you’re installing solar panels for the first time or expanding an existing system with battery storage, we provide honest advice, transparent quotations and fully compliant installations throughout Essex, Kent, Suffolk, Hertfordshire and the surrounding South East and East Anglia.

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.

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