Battery Storage Installation: DNO G99 Application Process

Installing battery storage alongside your solar panels represents a significant step towards energy independence, but navigating the DNO G99 application process can seem daunting for many UK homeowners. With the rising popularity of solar batteries and home energy storage systems, understanding the regulatory requirements for connecting these systems to the grid has become essential. This comprehensive guide walks you through everything you need to know about the G99 application process, from initial planning to final approval, ensuring your battery storage installation meets all necessary compliance standards whilst maximising your investment in renewable energy.

Understanding G99 Applications and DNO Requirements

The G99 application is a mandatory regulatory process for connecting larger-scale generation and storage systems to the UK electricity network. Introduced in April 2019, G99 replaced the previous G59 standard and applies to all installations with a capacity greater than 16A per phase (approximately 3.68kW on a single-phase supply or 11kW on a three-phase supply).

Your Distribution Network Operator (DNO) is the company responsible for maintaining the electricity distribution network in your area. In the UK, there are six main DNOs:

• UK Power Networks (London, South East, and East of England)
• Western Power Distribution (Midlands, South West, and Wales)
• Northern Powergrid (Yorkshire and North East)
• Scottish Power Energy Networks (Central and Southern Scotland)
• Scottish and Southern Electricity Networks (Central Southern England and Northern Scotland)
• Electricity North West (North West England)

Each DNO has slightly different procedures and timescales, though all follow the fundamental G99 framework. The application ensures your battery storage system won’t adversely affect the local network’s stability or safety.

When Is a G99 Application Required for Battery Storage?

Not all battery storage installations require a G99 application. The determining factors include:

• System capacity: If your combined solar and battery inverter capacity exceeds 3.68kW (single-phase) or 11kW (three-phase), G99 applies
• Export capability: Systems that can export more than 16A per phase to the grid require G99 approval
• Existing installations: Adding battery storage to an existing solar system may trigger G99 requirements if the combined capacity exceeds thresholds
• AC-coupled systems: These typically require G99 as they involve additional inverter capacity

For smaller domestic installations under these thresholds, the simpler G98 notification process applies instead. Your installer should assess which application route is appropriate for your specific circumstances.

The G99 Application Process Step-by-Step

The G99 application process typically takes 45-65 working days from submission to approval, though this can vary significantly depending on your DNO and local network conditions.

Stage 1: Pre-Application Assessment (Days 1-7)

Your installer will conduct a detailed site survey, assessing your property’s electrical infrastructure, existing solar installation (if applicable), and proposed battery storage system. They’ll gather essential information including:

• Maximum Power Point (MPP) reference number
• Existing generation capacity
• Proposed battery inverter specifications
• Single-line electrical diagrams
• Equipment data sheets and G99 type test certificates

Stage 2: Application Submission (Days 8-10)

The formal G99 application is submitted to your DNO through their online portal or via email. The submission package includes:

• Completed G99 application forms
• Technical specifications for all equipment
• Site location plans and electrical schematics
• Evidence of installer competency (MCS certification)
• Application fee (typically £350-£600 depending on system size)

Stage 3: DNO Assessment (Days 11-55)

Your DNO reviews the application, conducting network studies to determine if your proposed installation can be safely accommodated. They assess:

• Local network capacity
• Voltage regulation impacts
• Fault level contributions
• Power quality considerations

During this period, the DNO may request additional information or clarifications. Prompt responses help avoid delays.

Stage 4: Offer and Acceptance (Days 56-65)

If approved, you’ll receive a formal connection offer outlining any conditions or network reinforcement requirements. Most domestic battery storage installations receive standard offers without additional costs, but some may require network upgrades at the applicant’s expense.

Common Challenges and How to Avoid Delays

Understanding potential pitfalls can help streamline your G99 application process and avoid costly delays.

Incomplete Documentation

The most common cause of delays is missing or incorrect information. Ensure your installer provides:

• Accurate single-line diagrams matching the proposed installation
• Valid G99 type test certificates for all equipment
• Correct MPAN (Meter Point Administration Number) details
• Clear site location plans with GPS coordinates

Network Constraints

Some areas, particularly rural locations in Scotland, Wales, and Cornwall, face network capacity limitations. Your DNO may offer alternative solutions such as:

• Export limitation schemes
• Timed connection agreements
• Alternative connection points

Equipment Compliance Issues

Only use battery storage systems and inverters with valid G99 type test certification. Popular approved brands include Tesla Powerwall, GivEnergy, SolarEdge, and Enphase. Non-compliant equipment will result in automatic application rejection.

Costs Associated with G99 Applications

Understanding the full cost implications helps budget appropriately for your battery storage project.

Application Fees

DNO application fees vary by region and system size:

• Standard domestic applications (up to 50kW): £350-£600
• Larger residential systems (50-150kW): £600-£1,500
• Witness testing (if required): £500-£1,000

Professional Services

Most installers include G99 application management within their installation quote, typically adding £500-£1,000 to the overall project cost. This covers:

• Technical documentation preparation
• Application submission and management
• DNO liaison and correspondence
• Commissioning documentation

Potential Network Reinforcement

Whilst uncommon for domestic installations, some properties may require network upgrades costing £2,000-£10,000. Your DNO will identify these requirements during the assessment phase, allowing you to decide whether to proceed.

Timeline Expectations and Regional Variations

G99 processing times vary significantly across UK regions, influenced by DNO workload and local network complexity.

Fastest Processing Regions

• London and South East (UK Power Networks): 35-45 working days average
• North West (Electricity North West): 40-50 working days average

Slower Processing Regions

• Scotland (SSEN/SPEN): 50-70 working days average
• Wales and South West (Western Power): 45-65 working days average

Urban areas generally experience faster processing than rural locations due to better network infrastructure and fewer capacity constraints.

Post-Approval Requirements and Commissioning

Receiving G99 approval marks a significant milestone, but several steps remain before your battery storage system becomes operational.

Installation and Commissioning

Following approval, your installer can proceed with the physical installation. Post-installation requirements include:

• Commissioning tests per G99 requirements
• Submission of commissioning forms to the DNO
• Installation of required safety labels and signage
• Configuration of export limitation settings (if applicable)

Ongoing Compliance

Maintaining G99 compliance requires:

• Annual declaration of continued compliance (for systems over 50kW)
• Notification of any system modifications
• Cooperation with DNO network studies or inspections
• Maintaining equipment in accordance with manufacturer specifications

Future-Proofing Your Installation

With the UK’s commitment to net-zero emissions by 2050, battery storage systems will play an increasingly important role in the energy landscape. Consider these factors when planning your installation:

Scalability

Choose systems that allow future expansion without requiring new G99 applications. Modular battery systems from manufacturers like GivEnergy and Pylontech offer flexibility for growing energy needs.

Smart Grid Integration

Select equipment compatible with emerging smart grid technologies, enabling participation in future flexibility services and time-of-use tariffs. This could generate additional income streams from your battery storage system.

Vehicle-to-Grid Readiness

As electric vehicle adoption accelerates, consider how your battery storage system might integrate with future V2G (vehicle-to-grid) capabilities, potentially requiring additional G99 considerations.

Conclusion

Successfully navigating the G99 application process for battery storage installation requires careful planning, accurate documentation, and patience. Whilst the process may seem complex, working with experienced MCS-certified installers who understand your local DNO’s requirements significantly improves the likelihood of smooth approval. As battery storage technology continues to evolve and become more affordable, with prices dropping from £800-£1,000 per kWh in 2020 to £400-£600 per kWh in 2024, the investment case strengthens despite the regulatory requirements. By understanding the G99 process, you’re better positioned to make informed decisions about your battery storage installation, ensuring compliance whilst maximising the benefits of energy independence and reduced electricity bills. Remember that whilst the application process typically takes 6-10 weeks, the long-term benefits of properly installed and approved battery storage—including potential savings of £500-£900 annually on electricity bills—make the initial regulatory hurdles worthwhile for most UK homeowners.