G99 Application for Solar Panels in the UK: A Homeowner’s Guide
A G99 application is the process used to obtain permission from your local Distribution Network Operator, or DNO, before connecting certain solar panel, battery or other electricity-generating systems to the grid.
For most single-phase homes, G99 is normally required when the system’s registered output exceeds 3.68kW, equivalent to 16A per phase. Smaller, fully type-tested systems may qualify for the simpler G98 process instead.
This guide explains whether you need G99 approval, how it differs from G98, what your installer submits, likely timescales, export limitations and possible costs. It is for homeowners, landlords, renovators, EV owners and small businesses considering a larger solar or solar-and-battery system.
Quick answer
You will usually need a G99 application when a grid-connected solar or battery system can generate more than 16A per phase. On a typical single-phase home, that is 3.68kW. On a balanced three-phase supply, it is approximately 11.04kW in total.
Unlike G98, which normally allows qualifying equipment to be installed first and notified afterwards, standard G99 requires an application and DNO authorisation before installation proceeds. The DNO may approve the requested capacity, impose an export limit, request design changes or require work on the local network.
G98, G99 and G99 Fast Track compared
| Route | Typical eligibility | DNO process | Common use |
|---|---|---|---|
| G98 | Fully type-tested generation up to 16A per phase | Notify the DNO within 28 days after commissioning | Smaller domestic systems, often using a 3.68kW single-phase inverter |
| Standard G99 | More than 16A per phase or outside G98 conditions | Apply and obtain approval before connection | Larger domestic solar, commercial solar and higher-output batteries |
| G99 Fast Track or Small Generation Installation | Qualifying type-tested generation and storage, sometimes with an export limit | Application or notification depends on the relevant category | Eligible solar-and-battery systems within defined equipment and export ratings |
The exact Fast Track route depends on the combined equipment ratings, type-test status and whether an approved export limitation scheme is used. Some eligible applications can receive a response within approximately ten working days.
What is a G99 application?
G99 is an Energy Networks Association engineering recommendation covering generators that operate in parallel with the public electricity distribution network. Solar PV is included because its inverter can send electricity into the local cables serving neighbouring properties.
The DNO is not your electricity supplier. It owns and operates the regional network and assesses whether a proposed connection could create excessive voltage rise, overload equipment, interfere with protection systems or reduce power quality.
G99 approval is separate from:
- Planning permission
- Building Regulations compliance
- MCS certification
- Electrical installation certification
- Smart Export Guarantee registration
A solar project may require several of these, but one does not replace another.
Great Britain currently uses EREC G99 Issue 2, supported by the ENA’s current G98/G99 connection guide and application forms. Northern Ireland has separate G99/NI requirements, so properties there should follow the current NIE Networks process.
Do your solar panels need G99?
The first number to check is not simply the solar panels’ DC capacity. The critical figure is normally the registered AC capacity of the inverter or combined generating equipment connected at the property.
For example, a roof might carry 5kWp of solar panels while using a type-tested 3.68kW inverter. The completed design may remain within G98. By contrast, a 5kW single-phase inverter would normally require G99 because its output exceeds 16A per phase.
Your installer must also consider:
- Existing solar panels or batteries
- Multiple inverters that can operate simultaneously
- Whether the property has single-phase or three-phase power
- The equipment’s ENA type-test status
- Maximum registered capacity
- Manufacturer-set power limitations
- Vehicle-to-grid equipment
- Any proposed G100 export limitation scheme
The ENA rules consider the combined generating capacity at the premises, not merely one new device in isolation.
Do not automatically reduce the number of panels simply to avoid G99. A larger panel array paired with an appropriately sized inverter can improve production during winter, cloudy weather and the morning and evening periods. The right design should reflect annual generation, household demand, battery use, export value and the capacity permitted by the DNO.
The G99 application process
1. Confirm the DNO and electricity supply
The installer identifies the network operator using the property postcode and checks the MPAN, supply phase, service rating and existing generation.
Some new-build developments are connected through an Independent Distribution Network Operator rather than one of the main regional DNOs. The ENA provides a postcode-based network-operator finder.
2. Finalise the technical design
The application requires defined equipment rather than an approximate proposal. It should state the panel capacity, inverter, battery, protection, isolators, connection arrangement and proposed maximum export.
Changing the inverter or export-control equipment after approval may require the application to be amended.
3. Prepare the documents
A smaller G99 application commonly includes:
- The appropriate application form
- Property address and MPAN
- Site and location plans
- A single-line electrical schematic
- Inverter and battery specifications
- ENA type-test reference numbers
- Installer and customer details
- A signed letter of authority where required
Larger or non-type-tested systems may need further engineering and compliance information.
4. Apply before installation
G99 is generally an apply-to-connect process. The application must be sent before installation so that the DNO can assess the proposal and issue its approval or connection offer.
5. Review the DNO decision
The DNO may:
- Approve the requested capacity
- Approve a lower export capacity
- Require a G100 export limiter
- Request additional information
- Propose changes to the design
- Quote for network reinforcement
Your installer should explain the technical and financial implications before you accept the offer.
6. Install and commission
The completed installation must match the approved design. Protection settings, export controls and shutdown behaviour must be configured and tested correctly. Some projects may require witnessed testing by the DNO.
7. Submit completion documents
After commissioning, the installer normally sends the required installation and commissioning confirmation within 28 days. Keep the DNO approval, MCS certificate, electrical certificates, warranties and approved system settings with your property records.
What does the DNO assess?
The DNO checks whether the local network can safely accommodate the proposed generation. Its assessment may consider:
- Voltage rise
- Cable and transformer capacity
- Fault contribution
- Phase balance
- Protection operation
- Power quality
- Existing generation nearby
Two apparently similar homes can therefore receive different decisions. Available capacity depends on the local transformer, feeder, cables and existing connections—not simply the homeowner’s annual electricity consumption.
An approval may specify an Agreed Export Capacity below the inverter’s maximum output. Solar electricity can still supply the home, charge a battery, heat water or charge an EV before any surplus reaches the export limit.
Export limitations and G100
A G100-compliant Export Limitation Scheme measures power at the grid connection and controls the inverter or another device so that export remains below the agreed limit.
The scheme must react quickly and operate on a fail-safe basis. If communications or control components fail, it must reduce export to the permitted level.
An export limiter can enable a larger solar or battery system where unrestricted export would otherwise require expensive network reinforcement.
However, specifying “zero export” does not automatically remove the need for a DNO application. The generating equipment remains electrically connected in parallel with the network, and the export-control arrangement must be assessed and accepted.
Batteries and future upgrades
Battery energy and battery power are different.
A 13.5kWh battery rating describes how much energy the battery stores. Its inverter rating in kW describes how quickly it can charge or discharge. G99 assessment considers the electrical power that the equipment could place on the network.
Battery storage can therefore require a G99 application even without new solar panels. National Grid’s guidance confirms that storage capable of exporting should follow the appropriate generation-connection process.
Tell your installer about plans for additional batteries, a second inverter or vehicle-to-grid charging. Designing for future expansion may prevent duplicated paperwork, replacement switchgear or an undersized export limiter.
Any material change made later should be checked against the original DNO approval before equipment is added.
G99 costs and timescales
| Item | Typical domestic position | Practical advice |
|---|---|---|
| Installer administration | Often included in the solar quotation but sometimes charged separately | Confirm whether revisions and DNO correspondence are included |
| DNO assessment | Many straightforward small applications are free to submit; assessment, design or witnessing charges can arise | Request written confirmation of non-refundable charges |
| Standard low-voltage response | Up to 45 working days after complete information is received | Apply before booking installation dates or scaffolding |
| Fast Track | Eligible cases may be handled in about ten working days | Equipment ratings and export controls determine eligibility |
| Network reinforcement | May be unnecessary but can become substantial | Compare reinforcement with a reduced export capacity or revised design |
| Export limiter | Adds hardware, configuration and commissioning costs | Confirm DNO acceptance, fail-safe operation and capacity for future upgrades |
There is no single national customer price for a G99 project. Recent industry guides report that smaller applications are commonly free to submit, although an installer may charge for administration and the DNO may charge where design work, witnessing or network modifications are required. Accurate figures require a survey and DNO assessment.
Official guidance allows up to 45 working days for a low-voltage G99 decision once the DNO has complete information. During periods of high demand in 2026, some homeowners experienced longer waits, so the published period should be treated as a planning allowance rather than a guaranteed installation date.
Why the installer matters
A G99 application is not merely paperwork. Approval depends on accurate equipment ratings, matching type-test references, a clear schematic and a design that the DNO can properly assess.
Delays commonly occur when equipment names do not match their certificates, existing generation is omitted, the MPAN is incorrect or export assumptions are unclear.
A good installer should:
- Confirm the application route before taking a non-refundable equipment deposit.
- Explain panel capacity, inverter capacity and export capacity.
- Use type-tested equipment with current ENA references.
- Compare unrestricted and export-limited designs.
- Respond promptly to DNO technical questions.
- Commission the installation exactly as approved.
- Supply the final DNO confirmation.
Many export-tariff providers require evidence that the DNO has registered the completed installation before accepting an application.
How to choose the right system
Start with your electricity profile rather than simply filling every available section of roof.
Review:
- Annual electricity consumption
- Daytime electricity use
- Heat-pump or electric-heating plans
- EV mileage and charging patterns
- Battery charging and discharge requirements
- Expected future demand
- Available export tariffs
Request a written proposal stating the panel capacity in kWp, inverter rating in kW, battery capacity in kWh, battery power in kW, requested export capacity, supply phase and proposed DNO route.
Also check warranties, monitoring, backup capability, maintenance access and whether the installer can support the export-control settings throughout the system’s life.
The best solar system is not always the one with the largest headline output. It is the design that secures permission, produces useful energy throughout the year and matches how the property consumes electricity.
Book a free home survey: Simple Green Energy can assess roof suitability, electrical demand, battery options and likely DNO constraints before recommending a system.
Frequently asked questions (FAQs)
Clear answers about G99 applications, inverter capacity, DNO authorisation, application times and costs, export limits, zero-export systems, G100 controls and home batteries. Speak to Simple Green Energy .
Does your solar or battery system need G99 approval?
Speak with Simple Green Energy about inverter ratings, existing generation, battery storage, export capacity, G100 controls and the DNO application required for your proposed installation.
Check my G99 requirementsConclusion:
A G99 application is usually required when solar, battery or combined generation exceeds 16A per phase or falls outside the G98 requirements. It allows the DNO to confirm that the local network can accommodate the connection safely.
Confirm the equipment ratings, apply before installation, allow realistic assessment time and understand any export restriction before committing to the final design.
Book a free survey with Simple Green Energy to receive a system proposal based on your property, electricity use and local network requirements.
