Do UK Solar and Battery Systems Need a G99 Application?
The G99 application is something many UK homeowners only think about after choosing their solar panels or battery system. However, some installations need approval from the local Distribution Network Operator (DNO) before they can be connected. This usually applies to systems rated above 3.68kW on a single-phase supply, including certain battery additions. Smaller, fully type-tested systems fall under G98, while G99 requires approval before installation. If you are planning home energy storage, understanding the difference early can help you avoid delays and unexpected costs. What matters is the combined registered AC output of the generating equipment, not just the number of solar panels on your roof.
What Is a G99 Application?
A G99 application is a formal request to the local electricity network operator for permission to connect generation equipment that falls outside the simplified G98 process. The governing document is Engineering Recommendation G99, published by the Energy Networks Association (ENA). It sets technical requirements for connecting generating equipment to public distribution networks in Great Britain. It is an engineering recommendation applied through network connection requirements, rather than a standalone Act of Parliament.
Search what is a G99 application and the practical answer is straightforward: it is the approval process that allows a proposed solar or battery installation to connect safely to the local electricity network. The DNO assesses the equipment, its output and the capacity of the local network before giving permission.
It is also important to understand what the G99 regulations actually cover. G99 and G98 have different requirements, so meeting the manufacturer's equipment specifications alone does not mean you can connect your system to the grid. The technical requirements are set out in the current G99 Issue 2 document and its accompanying ENA application forms.
A G98 installation follows a different route: the installer connects eligible equipment and submits the required notification within 28 days. Under G99, approval comes first.
G98, G99 and G100 Compared
The three standards address different parts of connecting domestic generation to the electricity network.
Requirement | G98 | G99 | G100 |
Main purpose | Connect and notify | Apply and obtain approval | Control electricity exported to the grid |
Single-phase threshold | Up to 3.68kW per phase | Above 3.68kW per phase or equipment outside G98 | Agreed export limit |
Three-phase threshold | Up to 11.04kW total | Above 11.04kW total | Agreed three-phase export limit |
Application timing | Notification within 28 days after commissioning | Approval before connection | Limiter details included in the connection application |
Relevant paperwork | G98 notification | G99 application | Export limitation scheme evidence |
The important distinction is that G100 is an export limitation recommendation, not a separate replacement for G99. A compliant limiter restricts how much electricity reaches the grid, even when the inverter has a higher rated output.
The calculation is based on inverter capacity - not kWp panel capacity. For instance, if 5kWp solar panels are plugged into a 3.68kW inverter and the rest of the conditions for G98 are met, the output is still within the 5kW limit...
Note: This guide is general information, not technical or legal advice. Connection requirements are set out in the current ENA Engineering Recommendations (G98, G99 and G100), so confirm the correct route for your property with a qualified installer and your DNO. |
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Does Your Home Need a G99 Application?
A G99 application is required when the proposed generation installation exceeds the applicable G98 threshold or fails the relevant G98 requirements. The installer must calculate the registered output of the equipment at the property, including existing generation and additional AC-coupled battery inverters.
This is where homeowners sometimes make a costly assumption. A battery does not automatically sit outside the calculation because it stores electricity rather than generating it from sunlight. An AC coupled battery is an inverter of its own and the output will be added to the existing solar inverter. If the battery is shared with a hybrid inverter, then the registered capacity of the hybrid inverter is used to assess the battery.
Home installation | Combined output | Likely connection route |
4kWp panels with a 3.6kW hybrid inverter | 3.6kW | G98 |
5kWp panels with a 3.68kW inverter | 3.68kW | G98 |
6kWp panels with a 5kW inverter | 5kW | G99 |
Existing 3.6kW solar inverter plus 2.5kW AC battery inverter | 6.1kW | G99; fast-track eligibility requires assessment |
Replacement of a 3.68kW inverter with a 5kW unit | 5kW | G99 |
Three-phase property with 12kW of generation | 12kW | G99 |
Consider a household with an existing 3.68kW solar inverter that wants to add a 3kW AC battery inverter. The combined registered output is 6.68kW. That is above the single-phase G98 threshold, even though neither inverter individually exceeds 3.68kW.
Export limitation adds another consideration. A 5kW inverter restricted to 3.68kW of export has a 1.32kW difference between its rated output and permitted export. This is not an indication of the loss of generation, this is about what is fed back to the network by the limiter. It is up to the DNO to determine if the proposed arrangement is eligible for a simplified G99 route.
How to Apply for G99 Step by Step
A G99 application follows a defined process, although the paperwork differs between standard and fast-track installations. The installer normally handles the technical submission because the application requires equipment ratings, protection details and electrical drawings.
The ENA's Connect Direct platform provides an online route for installers to submit connection applications and notifications. It asks for the installation postcode, customer and installer details, equipment information and supporting documents.
Find Your DNO
The DNO G99 process starts with identifying the network operator responsible for the property's electricity distribution network. Your electricity supplier does not normally handle this approval.
The first two digits of the MPAN on an electricity bill provide a useful starting point, while the ENA's network operator information helps identify the relevant organisation.
Distribution Network Operator | Main service areas |
UK Power Networks | London, South East and East of England |
National Grid Electricity Distribution (NGED) | Midlands, South West and South Wales |
Northern Powergrid | North East England and Yorkshire |
Electricity North West | North West England |
SP Energy Networks | Central and Southern Scotland, Merseyside, Cheshire and North Wales |
Scottish and Southern Electricity Networks (SSEN) | Northern Scotland and Southern England |
NIE Networks | Northern Ireland |
A national grid G99 search needs one important distinction. National Grid Electricity Distribution, formerly Western Power Distribution, operates the Midlands, South West and South Wales distribution networks. It is not the same organisation as National Grid Electricity Transmission, which operates transmission infrastructure.
For a DNO G99 application, the installer submits the paperwork to the operator serving the installation address. A G99 DNO application therefore starts with the correct postcode and network operator, not the electricity supplier's name.
G99 Application Form and Documents
The G99 application form will include the proposed generating equipment and technical arrangements for connection. The appropriate version would be the one that is appropriate for the installation category and the DNO's existing submission process.
For smaller domestic systems, the main forms include:
A1-1: Standard application for relevant Type A generating installations.
A1-2: Application used for qualifying small-generation fast-track procedures.
A3-1: The standard small Type A route is installed with the installation notification shown below:
A3-2: Commissioning notification for applicable fast-track procedures.
A3-3: Notification for the relevant SGI-1 fast-track category.
The current DNO guidance and ENA forms determine which documents accompany each application.
Document | What it establishes | Common mistake |
Single-line diagram | Electrical connections between inverters, batteries, meter and limiter | Leaving out the battery inverter |
Site plan | Equipment location and property layout | Missing equipment positions |
Inverter and battery datasheets | Rated output and technical specifications | Confusing kWh with kW |
Export limitation details | Agreed export capacity and limiter arrangement | Giving a limit without supporting evidence |
MPAN and authority letter | Identifies the electricity supply and authorises the application | Supplying an incorrect MPAN |
A G99 certificate is not the name of one universal document issued by every DNO. Once approved, it is important for the homeowner to keep the DNO's written connection approval and the DNO's completed installation notification. An MCS certificate is not part of the network approval: it shows a certification of the installation by the appropriate scheme, not the replacement of network approval.
From Design to Commissioning
The application process is easier to follow when broken down into a few key steps:
Calculate the output: The installer adds the registered capacities of the relevant solar and battery inverters.
Identify the DNO: The property's postcode and MPAN help identify the local network operator responsible for approving the connection.
Check equipment: The installer checks the ENA Type Test Register and confirms the equipment's compliance evidence.
Prepare the documents: Technical drawings, equipment details and export limitation information are assembled.
Submit the application: Your installer sends the completed form and all supporting documents to the DNO for review.
Wait for approval: The DNO reviews the details and either approves the connection, sets conditions or asks for further information.
Complete the installation: Once approval is granted, the installer can proceed with the work, commission the system and submit the required notification. For the relevant small-generation routes, this must normally be done within 28 days.
A homeowner should not treat an application acknowledgement as permission to switch on the equipment. The DNO's actual connection approval is the important document.
Your G99 Application Checklist
Before accepting an installation date, ask the installer for the total inverter output in kW, the proposed export limit, the relevant DNO, the application route and the expected response period.
Keep the DNO decision, equipment datasheets, completed commissioning notification and MCS certificate together. These records will also help when upgrading the system later.
G99 Application Cost, Timelines and Fast Track
The G99 application cost is not one fixed national charge. The amount depends on the DNO, the type of connection assessment and any additional network work required.
There is also a difference between an application administration charge from an installer and a charge imposed by the network operator. Ask for these to be itemised separately.
G99 Fast Track vs Standard Application
The G99 fast track route is intended for small generation installations where the equipment complies with the technical conditions and the installation is qualified for the fast track route. This will alleviate assessment pressures, but is not a substitute for DNO confirmation.
SSEN identifies three Small Generation Installation categories. SGI-2 includes a basic design capacity of up to 7.36kW, with registered capacity and export conditions set by the category. SGI-3 is able to register a combined capacity of up to 14.72kW, depending on the individual equipment and export requirements.
Application route | Main paperwork | Published response period |
G98 | Notification | Submit within 28 days after commissioning |
G99 fast track | A1-2 for relevant SGI-2 and SGI-3 routes | SSEN aims for 10 working days |
G99 standard | A1-1 for relevant Type A installations | Up to 45 days for low-voltage applications |
The G99 fast track route is not available simply because a household has a small battery. The equipment must meet the relevant type-testing, capacity and export requirements. Some installations qualify for SGI-1 notification, while others need an A1-2 application.
The difference between a 10-working-day fast-track target and a 45-day standard response period is substantial. However, incomplete paperwork, additional technical studies and network constraints affect the actual installation schedule.
G99 Application Cost
The G99 application cost should be discussed before the installer submits the paperwork. Some domestic applications attract no separate DNO application fee, but that does not mean every connection is free.
Route | Potential cost | What to establish |
G98 notification | Usually no separate DNO application fee | Installer notification charge |
G99 fast track | Often no separate application fee | Installer administration and commissioning |
G99 standard | DNO-specific | Assessment and design charges |
Network reinforcement | Project-specific | Required cable, transformer or network upgrades |
Witness testing | Where required | DNO attendance and testing charges |
The DNO will advise the local network if reinforcement is required and include details of the work required and associated charges in their connection process. The installer should provide information on who is paying for the installation and if the proposed inverter size or export limit is a more economical design.
Note: Application fees, response times and fast-track eligibility vary by DNO and can change. Always confirm the current requirements with your DNO and installer before you commit to an installation date. |
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Delays, Rejections and Fixes
A rejected or delayed application often comes down to missing technical information rather than an inherently unsuitable solar system.
Common problems include an inverter missing from the ENA Type Test Register, an incomplete single-line diagram, an incorrect MPAN or a battery's energy capacity being entered instead of its inverter output.
A DNO request for further information also interrupts progress until the installer responds. The practical solution is to correct the drawings, supply the missing equipment evidence or revise the proposed output. A G100 export limitation scheme offers another route when the network operator accepts the proposed arrangement. Network reinforcement should be considered after the simpler design changes have been assessed.
How G99 Approval Affects Export and SEG
A G99 approval sets the conditions under which an installation connects to the local distribution network, including its permitted export capacity. It doesn't give an automatic infinite opportunity to export excess electricity to the grid.
This matters for households planning to receive payments through the Smart Export Guarantee (SEG). Ofgem's scheme requires participating electricity suppliers to pay eligible small-scale generators for electricity exported to the grid. Each supplier sets its own tariff rates and contract terms.
Getting paid for exported electricity involves a few separate steps:
DNO approval: Confirms how your system can connect to the grid and how much electricity it is allowed to export.
Export MPAN: Provides the metering point identification needed for the export arrangement.
SEG registration: The household applies to an eligible supplier and provides the evidence required by its tariff.
Installation certification: An MCS or Flexi-Orb certificate is relevant to the applicable supplier eligibility requirements.
The DNO approval letter and MCS certificate serve different purposes. Neither replaces the other.
Adding another inverter or battery also changes the technical information associated with the installation. Tell the installer and SEG supplier about the upgrade so that the connection records, export arrangements and equipment details remain consistent.
Planning Battery Storage Around Your Grid Connection
A G99 connection approval establishes how much generating capacity the local network accepts. Battery storage provides another way to manage the electricity produced by a solar array: instead of exporting every surplus unit immediately, the household stores some of it for later use.
This is particularly useful when an export limit restricts the electricity sent to the grid. The conditions of the DNO will not affect the storage, although it will enable more household generation to be utilised during the evening peak period.
Planning Solar and Storage From Scratch
Starting with a new solar installation gives the installer more freedom to design the inverter arrangement around the property's grid connection. For example, a 3,000W AC output at 230V represents approximately 13A, below the 16A single-phase G98 threshold on its own. Adding another inverter changes the total, so the proposed equipment must be assessed as one installation.
For a household without existing solar, EcoFlow STREAM 5000 is designed as a hybrid inverter option for a new solar and storage setup. Its 5kWh / 5024Wh capacity expands up to 90kWh, with 5000W PV input across four MPPT channels rated at 1,250W each. The AC output is 3000W, which is good for household electricity use and the small unit has a built-in handle. The G99 application route must be based on the final inverter capacity registered with the NEMC and not based on the capacity of the battery only, even if that battery is approved for export limitation.
Adding Storage to an Existing Solar System
A homeowner with an existing solar array faces a different design decision from someone starting with a new installation. The average energy cost for a 2019 semi-detached house with a 3.68kW solar inverter and G98 is $0.029 per unit. The total output is 6.68kW with the addition of a 3kW AC coupled battery inverter, thus exceeding the single-phase G98.
The G99 application needs to account for the additional inverter before the upgraded system is connected. EcoFlow STREAM AC 5000 is designed for households adding storage to existing solar installations. Its 5kWh / 5024Wh capacity is expandable up to 90kWh, while its 3000W AC output supports household energy use. Intelligent Mode+ manages energy use automatically, and Local Mode keeps operation available offline. The installer must confirm the equipment's ENA Type Test Register status, system configuration and appropriate DNO application route before installation.
Note: Compliant generation-only plug-in solar kits have been legal to buy and use in Great Britain since 27 August 2026, but these rules do not cover plug-in batteries or solar-plus-storage systems. Home batteries as well as systems with integrated batteries (such as EcoFlow STREAM) can be used legally only if installed by a properly qualified person in accordance with IET Wiring Regulations (BS 7671) and the requirements for connection to DNO.
Conclusion
A G99 application is essential for domestic solar and battery installations that fall outside the G98 connection rules. The main test is the combined registered inverter output against 3.68kW per phase. Fast-track applications are for qualified equipment, and are carried out through a shorter assessment process, or standard applications are carried out through a fuller technical assessment process. The conditions for electricity exports, too, are prescribed in DNO approval, but it does not automatically give SEG registration.
The ability to store electricity at home enables better utilization of generated surplus electricity within the limits of connection. Visit the EcoFlow UK website to learn more about the EcoFlow STREAM 5000 and EcoFlow STREAM AC 5000, and discover the perfect option for solar energy storage in your home.
FAQ About the G99 Application
Does a G99 application replace planning permission?
No. Network approval and planning permission are not one and have separate processes. Many domestic solar installations can be considered permitted development; however, there are exceptions for listed buildings and some conservation areas. Please check with the local planning authority before installing, as appropriate.
Do EV chargers and heat pumps need a G99 application?
Standard EV chargers and heat pumps are electricity-consuming equipment, not generating systems, so G99 is not their normal connection route. The installation still requires relevant DNO notification and/or connection requirements. Bidirectional V2G equipment is unique in that it exports electricity, and has to undergo an assessment on the connection of the generation equipment.
What happens if I install solar without a G99 application?
Connecting equipment that requires prior approval without obtaining it breaches the applicable connection requirements. The DNO can require the installation to be disconnected until the issue is resolved. Contact the installer and the DNO to arrange the correct retrospective assessment. Export arrangements and SEG registration also need to be regularised.