DNO Applications: Grid Connection for UK Solar Systems

Connecting your solar panel system to the national grid requires more than just installation expertise—it demands proper authorisation from your local Distribution Network Operator (DNO). This crucial step in the solar installation process ensures your system can safely export excess electricity whilst maintaining grid stability across the UK’s complex energy infrastructure. Understanding DNO applications and G99 regulations can help homeowners navigate this essential requirement and avoid costly delays in their renewable energy journey.

What Is a DNO Application?

A DNO application is a formal request submitted to your regional Distribution Network Operator for permission to connect your solar panel system to the electricity grid. Think of it as planning permission for your electrical connection—just as you wouldn’t build an extension without council approval, you can’t connect renewable energy systems without DNO consent.

Your DNO manages the electricity distribution network in your area, maintaining the cables and infrastructure that deliver power to homes and businesses. In the UK, there are six main DNOs covering different regions:

• UK Power Networks: London, South East, and East of England
• Northern Powergrid: Yorkshire and the North East
• Electricity North West: Manchester, Lancashire, and Cumbria
• Western Power Distribution: Midlands, South West, and Wales
• Scottish Power Energy Networks: Central and Southern Scotland, Merseyside, and North Wales
• Scottish and Southern Electricity Networks: Central Southern England and Northern Scotland

The application process ensures your solar installation won’t cause voltage fluctuations, overload local transformers, or create safety hazards for network engineers working on the grid.

Understanding G99 Regulations

G99 regulations, formally known as ‘Requirements for the connection of generation equipment in parallel with public distribution networks’, came into effect in April 2019, replacing the previous G83 and G59 standards. These technical requirements govern how renewable energy systems connect to and interact with the national grid.

The regulations establish different categories based on your system’s capacity:

• Type A (up to 16A per phase): Most domestic installations under 3.68kW per phase
• Type B (16A to 100A per phase): Larger domestic and small commercial systems
• Type C and D: Commercial and industrial installations

For typical UK households, most solar installations fall under Type A or B classifications. Systems up to 3.68kW per phase (11kW for three-phase connections) can often use a simplified notification process, whilst larger systems require full application and potentially witness testing.

Key G99 Requirements Include:

• Protection settings to prevent ‘islanding’ (continuing to generate when the grid fails)
• Power quality standards to minimise harmonic distortion
• Voltage and frequency operating ranges
• Remote monitoring capabilities for larger systems
• Compliance with loss of mains protection standards

The DNO Application Process

Navigating the DNO application process requires careful attention to detail and proper documentation. Most reputable solar installers handle this process on behalf of homeowners, but understanding the steps helps ensure nothing gets overlooked.

Pre-Application Stage

Before submitting your application, your installer should conduct a thorough site assessment, including:

• Checking your current electrical installation and consumer unit
• Assessing the local network capacity
• Determining the appropriate application type
• Gathering technical specifications for all equipment

Application Submission

The formal application typically includes:

• Completed G99 application forms
• Single line diagrams showing the proposed installation
• Equipment data sheets and type test certificates
• Site location plans and OS grid references
• Protection settings schedules
• Installer’s accreditation details (MCS certification)

Applications are usually submitted online through your DNO’s portal, with processing times varying from 15 to 45 working days depending on complexity.

DNO Assessment

Your DNO reviews the application against network constraints, checking whether the local infrastructure can accommodate your proposed generation capacity. They may request additional information or suggest modifications to ensure grid stability.

Export Limitations and Solutions

Not all properties receive unrestricted export approval. In areas with high solar uptake, such as Cornwall, parts of East Anglia, and rural Scotland, network constraints may limit how much electricity you can export to the grid.

Common Export Scenarios:

• Full export approval: No restrictions on sending excess generation to the grid
• Limited export: Capped at a specific rate (e.g., 3.68kW or 5kW)
• Zero export: Generation for self-consumption only

If you face export limitations, several solutions exist:

• Export limiting devices: Automatically restrict grid export whilst allowing full generation for home use (£300-£500)
• Battery storage: Store excess generation for evening use (£4,000-£8,000 for typical systems)
• Hot water diverters: Channel surplus electricity to heat water (£500-£800)
• Network reinforcement: Pay for grid upgrades (costs vary significantly)

Costs and Timescales

Understanding the financial and time implications of DNO applications helps set realistic expectations for your solar project.

Application Fees

DNO application costs vary by region and system size:

• Standard domestic applications (up to 3.68kW per phase): Usually free
• Larger domestic systems (4-10kW): £150-£350
• Complex applications requiring studies: £500-£1,500
• Witness testing (if required): £500-£1,000

Processing Times

Typical timescales from application to approval:

• Connect and notify (up to 3.68kW): Immediate connection, notify within 28 days
• Standard applications: 15-45 working days
• Complex applications: 45-65 working days
• Applications requiring network studies: 3-6 months

Delays can occur during peak periods (spring and summer) when DNOs receive higher application volumes. Planning your installation for autumn or winter may result in faster processing.

Regional Variations Across the UK

Different regions face unique challenges and opportunities regarding grid connections. Understanding your local context helps anticipate potential issues.

High Solar Density Areas

Regions with extensive solar adoption may experience network constraints:

• South West England: Cornwall and Devon often face export limitations due to rural network capacity
• East Anglia: High agricultural solar deployment affects residential applications
• South Coast: Brighton to Bournemouth corridor seeing increased restrictions

Urban Versus Rural Considerations

Urban areas like London, Birmingham, and Manchester typically have robust grid infrastructure supporting higher export capacities. However, listed buildings and conservation areas may face additional planning hurdles.

Rural properties, particularly in Scotland, Wales, and Northern England, might encounter weak grid connections requiring expensive upgrades. Single-phase supplies common in countryside locations limit system sizes to around 3.68kW without upgrading to three-phase (£3,000-£8,000).

Smart Export Guarantee and Grid Connection

The Smart Export Guarantee (SEG), launched in January 2020, requires energy suppliers to pay for exported solar electricity. However, receiving SEG payments depends on having proper DNO approval and export metering.

Current SEG Rates (2024)

• Octopus Energy: 15p per kWh (Intelligent Octopus customers)
• British Gas: 6.4p per kWh
• E.ON: 5.5p per kWh
• EDF Energy: 5.6p per kWh

Without DNO approval for export, you cannot claim SEG payments, potentially losing £200-£400 annually for typical domestic systems. This makes proper grid connection essential for maximising your solar investment returns.

Common DNO Application Mistakes to Avoid

Learning from others’ errors can streamline your application process and prevent costly delays.

Documentation Errors

• Submitting outdated G83 forms instead of current G99 documentation
• Incomplete technical specifications for inverters and panels
• Missing or incorrect single line diagrams
• Failing to include MCS certificates

Technical Oversights

• Proposing incompatible inverter settings
• Ignoring local network voltage issues
• Underestimating total system capacity when adding to existing generation
• Not accounting for future expansion plans

Process Mistakes

• Installing equipment before receiving DNO approval
• Using non-accredited installers for grid-connected systems
• Failing to notify DNO of system modifications
• Missing response deadlines for additional information requests

Future Developments in Grid Connection

The UK’s grid connection landscape continues evolving with technological advances and policy changes. Upcoming developments include:

• Flexible connections: Dynamic export limits based on real-time network capacity
• Local energy markets: Peer-to-peer trading within communities
• Vehicle-to-grid integration: Electric vehicles supporting network stability
• Streamlined applications: Digitalisation reducing processing times

The government’s commitment to 70GW of solar capacity by 2035 necessitates grid infrastructure improvements, potentially easing current connection constraints.

Conclusion

Securing DNO approval represents a critical milestone in your solar installation journey, ensuring safe, compliant grid connection whilst maximising your system’s financial benefits through export payments. Whilst the application process might seem daunting, working with experienced MCS-certified installers who understand G99 regulations and regional DNO requirements significantly simplifies the process. As the UK accelerates towards net-zero targets, expect continued improvements in grid connection procedures, making solar adoption increasingly accessible for homeowners across all regions. By understanding DNO applications now, you’re better positioned to navigate this essential step and join the growing community of UK solar generators contributing to our sustainable energy future.