Solar Battery Ready Systems: G98 vs G99 Connection Rules

As the UK continues its transition towards renewable energy, more homeowners are considering solar panel installations with battery storage systems. However, navigating the technical regulations surrounding grid connections can be daunting. Two critical standards govern how solar and battery systems connect to the national grid: G98 and G99. Understanding these connection rules is essential for anyone planning to install a solar battery ready system, as they directly impact installation costs, timescales, and the overall feasibility of your renewable energy project.

Understanding Grid Connection Standards in the UK

The UK’s electricity network operates under strict regulations to maintain grid stability and safety. When you install a solar panel system with or without battery storage, you’re essentially becoming a mini power station that can export electricity back to the grid. This requires compliance with specific technical standards set by the Energy Networks Association (ENA).

These standards ensure that distributed generation systems don’t compromise the integrity of the local electricity network. They define parameters such as:

• Maximum export capacity allowed
• Safety disconnection requirements
• Power quality standards
• Installation notification procedures
• Testing and commissioning requirements

The two primary standards, G98 and G99, replaced the older G83 and G59 regulations in 2019, providing clearer guidelines for modern renewable energy installations.

What is G98? Small-Scale Embedded Generators

G98 is the engineering recommendation for the connection of small-scale embedded generators (up to and including 16 amps per phase) in parallel with public low-voltage distribution networks. In practical terms, this covers most domestic solar installations.

Key Features of G98 Connections

For single-phase properties (the vast majority of UK homes), G98 allows installations up to 3.68kW without requiring prior approval from your Distribution Network Operator (DNO). For three-phase properties, this limit extends to 11.04kW. These systems can be:

• Installed using a simplified notification process
• Connected without expensive grid studies
• Commissioned within days rather than weeks
• Installed at lower costs due to reduced administrative requirements

The streamlined G98 process typically costs between £0-150 for the DNO application, making it the most economical choice for residential installations. Most installers in areas like Birmingham, Manchester, and Leeds report that over 80% of domestic solar installations fall within G98 limits.

What is G99? Large-Scale Embedded Generators

G99 covers larger installations exceeding the G98 thresholds, typically commercial properties, solar farms, or ambitious domestic installations with substantial battery storage. This standard applies to systems above 3.68kW for single-phase or 11.04kW for three-phase connections.

Key Requirements for G99 Connections

G99 installations require a more rigorous approval process:

• Pre-application with detailed technical specifications
• Potential grid reinforcement studies (£500-£2,000)
• Witness testing by DNO representatives
• Extended lead times of 8-12 weeks
• Higher connection costs ranging from £1,500-£10,000+

In Scotland, particularly in rural areas served by Scottish and Southern Electricity Networks (SSEN), G99 applications may face additional scrutiny due to weaker grid infrastructure. Urban areas like Edinburgh and Glasgow typically have more robust networks, potentially reducing connection costs and approval times.

Solar Battery Integration: Impact on Connection Rules

Adding battery storage to your solar system significantly affects which connection standard applies. Whilst solar panels alone might fall within G98 limits, the addition of batteries can push your system into G99 territory.

The critical factor is your system’s maximum export capacity – the total power that could theoretically be exported to the grid at any moment. This includes:

• Solar panel generation capacity
• Battery inverter discharge capacity
• Any AC-coupled battery systems

For example, a 3.5kW solar array paired with a 5kW battery inverter creates an 8.5kW total export capacity, requiring G99 approval despite the modest solar capacity. However, export limitation devices can restrict grid export to G98 levels whilst maintaining larger internal capacities.

Smart Export Limitation Solutions

Modern inverters from manufacturers like SolarEdge, Fronius, and GivEnergy offer export limitation features that can keep your system within G98 boundaries. These systems cost an additional £200-500 but can save thousands in G99 connection fees. They’re particularly popular in the Southeast, where DNOs like UK Power Networks actively promote their use.

Cost Implications: G98 vs G99 Installations

The financial difference between G98 and G99 installations extends beyond initial connection fees. Understanding these costs helps homeowners make informed decisions about system sizing and configuration.

Typical G98 Installation Costs

• DNO application: £0-150
• Installation timeframe: 2-4 weeks
• No additional equipment required
• Total system cost (4kW solar + 5kWh battery): £8,000-10,000

Typical G99 Installation Costs

• DNO application and studies: £1,500-5,000
• Installation timeframe: 8-16 weeks
• Potential G99 relay requirement: £500-1,000
• Possible grid reinforcement: £2,000-20,000
• Total system cost (6kW solar + 10kWh battery): £12,000-18,000

In Wales, where the grid infrastructure varies significantly between urban centres like Cardiff and rural areas in Powys, G99 costs can be particularly unpredictable. Some rural installations have faced grid reinforcement quotes exceeding £30,000.

Regional DNO Variations Across the UK

The UK’s electricity distribution is managed by different DNOs, each with slightly different interpretations and implementations of G98 and G99 rules. Understanding your local DNO’s approach is crucial for planning your installation.

DNO-Specific Considerations

Western Power Distribution (Midlands, Southwest, South Wales): Generally accommodating with clear online application processes. Average G99 approval time: 10 weeks.

Northern Powergrid (Northeast, Yorkshire): Known for thorough technical assessments. Often requires detailed single-line diagrams even for G98 applications.

Scottish and Southern Electricity Networks (Scotland, Southern England): Variable approach depending on location. Highland installations face stricter scrutiny than those in Portsmouth or Southampton.

UK Power Networks (London, Southeast, East): Progressive approach to battery storage, with dedicated teams for renewable connections. Fastest G99 approvals in urban areas.

Electricity North West (Northwest): Pragmatic approach with good support for export limitation devices. Manchester and Liverpool benefit from robust grid infrastructure.

SP Energy Networks (Merseyside, North Wales, Scotland): Increasingly supportive of domestic battery storage, with streamlined processes for standard configurations.

Future-Proofing Your Solar Battery System

With battery prices falling and electricity costs rising, many homeowners want systems that can expand over time. Planning for future expansion whilst staying within favourable connection rules requires strategic thinking.

Strategies for Scalable Systems

Consider installing G99-ready infrastructure even if starting with a G98 system. This includes:

• Oversized consumer units with spare ways
• Pre-installed DC and AC isolation switches
• Cable routes for future battery connections
• Hybrid inverters capable of AC and DC coupling

Many installers in Bristol, Nottingham, and Newcastle now offer ‘battery-ready’ packages that include the necessary infrastructure for future upgrades. These typically add £500-800 to installation costs but can save £1,500-2,000 when adding batteries later.

Modular Battery Systems

Manufacturers like Tesla, GivEnergy, and Pylontech offer modular battery systems that can start small and expand. Beginning with a 5kWh battery under G98 rules and adding modules later (potentially moving to G99) provides flexibility whilst managing initial costs.

Making the Right Choice for Your Property

Choosing between G98 and G99 isn’t always straightforward. Your decision should consider immediate needs, future plans, and local grid constraints.

When G98 Makes Sense

• Standard 3-4 bedroom homes with typical energy consumption
• Budget-conscious installations prioritising quick payback
• Properties in areas with grid constraints
• First-time solar adopters wanting proven technology

When G99 is Worth Considering

• Large properties with high energy demands
• Homes with electric vehicle charging requirements
• Properties planning heat pump installations
• Households seeking maximum energy independence
• Commercial properties or home businesses

Consulting with MCS-certified installers who understand local DNO requirements is essential. They can model different scenarios and provide accurate cost-benefit analyses based on your specific circumstances.

Conclusion

Understanding G98 and G99 connection rules is fundamental to planning a successful solar battery installation in the UK. Whilst G98 offers a simpler, more affordable route for most domestic properties, G99 opens possibilities for larger, more comprehensive renewable energy systems. The key is balancing your energy independence goals with practical considerations like installation costs, approval timescales, and local grid capacity. As battery technology continues to advance and costs decrease, export limitation devices and smart energy management systems increasingly allow homeowners to maximise their renewable energy capabilities whilst working within existing regulatory frameworks. Whether you’re in London, Birmingham, or rural Scotland, taking time to understand these connection rules ensures your solar battery system delivers optimal performance and value for years to come.