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G99 Grid Connection for Commercial Solar: Complete Guide
Understanding the G99 grid connection process for commercial solar installations over 50kW. Application steps, timelines, costs, and how to navigate UK Power Networks requirements in Essex.
Key Takeaway
Any commercial solar installation above 50kW requires a G99 grid connection application to the local Distribution Network Operator (DNO). In Essex, the DNO is UK Power Networks. The process typically takes 8-12 weeks and costs between £500 and £8,000+ depending on complexity. We manage the entire G99 process as part of our installation service.
What Is G99?
G99 is the Engineering Recommendation published by the Energy Networks Association (ENA) that governs the connection of generating equipment, including solar panels, to the UK distribution network. It replaced the previous G59 standard and sets out the technical requirements, application process, and commissioning procedures for connecting generation systems above the G98 threshold to the electricity grid.
The G99 process exists to ensure that distributed generation, such as commercial solar panels, can be safely connected to the electricity network without compromising the safety, reliability, or quality of supply for other network users. When a commercial solar system exports electricity to the grid, it changes the flow of power on the local network. The DNO must assess whether the network can accommodate this additional generation without causing voltage issues, thermal overloading, or protection coordination problems.
For businesses installing commercial solar panels, G99 is an essential regulatory requirement that must be addressed early in the project planning stage. The application should be submitted as soon as the system design is finalised, as the assessment timeline directly affects your project programme. Failing to account for G99 timelines is one of the most common causes of delay in commercial solar projects.
While the G99 process may seem complex, it is a well-established procedure that experienced solar installers manage routinely. At EC Eco Energy, we handle the entire G99 application process on behalf of our clients, from initial application through to commissioning confirmation, as a standard part of our commercial solar installation service.
When Is G99 Required?
The G99 application process is required for generating installations that exceed the thresholds set out in the G98 standard. In practical terms for commercial solar, this means:
| System Size | Connection Type | Process Required | Typical Timeline |
|---|---|---|---|
| Up to 3.68 kW (single phase) | G98 Type A | Notification only | Immediate |
| 3.68 kW - 50 kW | G98 Type B | Application (simplified) | 10-25 working days |
| 50 kW+ | G99 | Full application and assessment | 45-65 working days |
| 1 MW+ | G99 (enhanced) | Full application with detailed studies | 65+ working days |
Most commercial solar installations in the 50kW to 500kW range fall squarely within the G99 application process. Systems below 50kW qualify for the simpler G98 process, which is faster and less costly. This is one reason some businesses opt for a system size just below 50kW to avoid the G99 process, though this only makes sense if the G99 costs and timeline genuinely outweigh the benefit of a larger system. In most cases, the additional generation from a larger system easily justifies the G99 process.
The G99 Application Process
The G99 application follows a structured process defined by the ENA. Here is what to expect at each stage.
Pre-Application Assessment
Before submitting the formal application, we assess the local network capacity using publicly available DNO heat maps and network data. This helps identify potential constraints early and allows us to design the system to optimise the connection process. If the heat map shows significant available capacity, the application is likely to be straightforward. If capacity is limited, we can design the system with export limitation or adjust the size to avoid costly reinforcement.
Application Submission
The formal G99 application is submitted to the DNO (UK Power Networks in Essex) via their online portal. The application includes detailed technical information about the proposed installation: system capacity, inverter specifications, protection settings, single-line diagram, site location, and metering arrangements. An application fee is payable at this stage, typically £300-£500.
DNO Assessment
The DNO carries out a technical assessment of the proposed connection against the local network. This includes voltage rise analysis, fault level assessment, thermal capacity check, and protection coordination review. The assessment determines whether the existing network can accommodate the proposed generation without adverse effects. The standard assessment period is 45 working days for systems up to 1MW.
Connection Offer
Following the assessment, the DNO issues a connection offer. This may be a simple approval to connect with minimal or no works required, or it may include a requirement for network reinforcement at the applicant's cost. The offer specifies any connection charges, works required, and a timescale for completing the connection. You have 20 working days to accept or reject the offer.
Installation and Commissioning
Once the connection offer is accepted and any required DNO works are completed, the solar system can be installed and commissioned. Commissioning involves testing the system to confirm it meets all G99 technical requirements, including protection settings and export limitations if applicable. A commissioning confirmation form (G99/1-4) is submitted to the DNO, and the system is formally approved for operation.
G99 Timeline
The total timeline from application submission to system energisation varies depending on the complexity of the connection and whether network reinforcement is required.
| Stage | Straightforward | Complex |
|---|---|---|
| Pre-application assessment | 1-2 weeks | 2-3 weeks |
| DNO assessment | 6-9 weeks | 9-13 weeks |
| Offer acceptance | 1-2 weeks | 2-4 weeks |
| DNO connection works | 0-2 weeks | 4-12 weeks |
| Total | 8-12 weeks | 16-30 weeks |
The solar panel installation itself can proceed in parallel with the G99 process once the connection offer has been accepted. However, the system cannot be energised and connected to the grid until the G99 commissioning process is complete. Planning the installation to coincide with DNO works completion minimises the total project timeline.
We strongly recommend submitting the G99 application as the first step in the project, before finalising contracts or scheduling installation works. This prevents the G99 timeline from becoming the critical path that delays the entire project.
G99 Costs
The costs associated with the G99 process include application fees, assessment charges, and any connection or reinforcement works required by the DNO.
| Cost Element | Typical Range | Notes |
|---|---|---|
| Application fee | £300 - £500 | Non-refundable, paid at submission |
| Connection works (minimal) | £0 - £2,000 | Where existing network has capacity |
| Minor reinforcement | £2,000 - £8,000 | Local network upgrades (fuses, settings) |
| Major reinforcement | £8,000 - £50,000+ | Transformer upgrades, cable replacement |
| Export limiter (if required) | £1,000 - £3,000 | Alternative to reinforcement in some cases |
For the majority of commercial solar installations in Essex, G99 costs fall in the £500-£3,000 range. Major reinforcement is relatively uncommon for systems under 250kW in areas with adequate existing network capacity. However, in areas with constrained networks or where multiple generators have already connected, reinforcement requirements and costs can be significantly higher.
We include G99 costs in our all-inclusive quotations so there are no surprises. Where we identify potential for high G99 costs during the pre-application assessment, we discuss options with you before proceeding, including system downsizing or export limitation as cost-effective alternatives to expensive reinforcement works. For full pricing details, see our commercial solar cost guide.
UK Power Networks: The Essex DNO
UK Power Networks (UKPN) is the Distribution Network Operator responsible for the electricity distribution network across Essex, London, and the South East of England. As the DNO for our primary service area, we work with UKPN on a regular basis and have established strong working relationships with their connections team.
UKPN manages one of the largest distribution networks in the UK, serving approximately 8.4 million customers across three licence areas: Eastern Power Networks, London Power Networks, and South Eastern Power Networks. Essex falls within the Eastern Power Networks licence area.
UKPN provides an online portal for G99 applications and publishes network capacity heat maps that show available generation capacity across their network. These heat maps are an invaluable planning tool, allowing us to assess the likely complexity and cost of a G99 application before committing to the process. Areas shown in green typically have abundant capacity for new generation connections, while amber and red areas may require reinforcement.
Our experience working with UKPN across Essex means we understand their assessment processes, standard terms, and typical response times. This experience allows us to prepare applications that meet their requirements first time, minimising delays and ensuring the smoothest possible connection process for our clients.
2026 Grid Queue Reform — What It Means for Essex Businesses
In 2025, Ofgem and NESO implemented the largest grid queue reform in UK history, reducing the national connection queue from 722 GW to 283 GW (a 61% reduction) by removing speculative applications. UK Power Networks' Eastern Power Networks licence area has a Gate 2 capacity allocation of 3,085 MW. For commercial solar applicants under 1 MW, the reforms have primarily improved queue processing speed with minimal impact on standard G99 timelines. The 45-working-day assessment target for standard commercial connections remains in effect under UKPN's published G98/G99 FAQ (Version 10.0, February 2025).
Common Issues and Solutions
Insufficient Network Capacity
The most common issue is limited capacity on the local network, particularly in rural areas or on feeders already hosting significant generation. Solutions include accepting export limitation (zero or reduced export), reducing system size to match available capacity, or funding network reinforcement where the cost is justified by the project returns.
Voltage Rise Issues
Solar generation can cause voltage levels to rise on the local network, particularly at the end of long rural feeders. If voltage rise exceeds acceptable limits, the DNO may require reinforcement or export limitation. Modern inverters can provide reactive power support to help manage voltage levels, which may reduce or eliminate the need for network reinforcement.
Protection Coordination
Adding generation to the network changes the fault currents and can affect the coordination of protection devices. The DNO assessment includes a review of protection settings and may require adjustments to the existing network protection or specific protection requirements for the solar installation. This is a standard technical matter that experienced installers manage routinely.
Application Delays
DNO assessment timelines can sometimes extend beyond the standard 45 working days, particularly during periods of high application volume. Incomplete or incorrect applications are a common cause of additional delays. We ensure all applications are complete and technically accurate before submission, and we proactively follow up with the DNO to keep the process on track.
Shared Connection Costs
Where multiple generators are connecting to the same part of the network, the DNO may apportion reinforcement costs between applicants. This can work in your favour if another generator is already funding reinforcement that benefits your connection, or it may require negotiation if costs are being shared in a way that does not reflect the benefit each party receives.
Frequently Asked Questions
G98 applies to smaller generating installations up to 16A per phase (approximately 3.68kW single-phase or 11.04kW three-phase for Type A, and up to 50kW for Type B). G99 applies to all larger installations above these thresholds. The key practical difference is that G98 connections can be notified to the DNO and proceed without waiting for approval (Type A) or require a simpler application process (Type B), while G99 connections require a formal application, technical assessment, and DNO approval before the system can be connected and energised.
The standard timeline for a G99 application is 45 working days (approximately 9 weeks) for the DNO to complete their assessment and provide an offer. However, more complex applications or those requiring detailed network studies can take 65 working days or longer. If network reinforcement is required, the total timeline from application to energisation can extend to 16-20 weeks or more. We typically advise businesses to allow 8-12 weeks for straightforward G99 applications and up to 20 weeks for complex cases.
G99 application costs vary depending on the system size and complexity. The initial application fee is typically £300-£500. If the DNO assessment identifies that network reinforcement or upgrades are required, these costs can range from a few thousand pounds to £50,000 or more in extreme cases. For most commercial solar installations in areas with adequate grid capacity, total G99 costs including connection works fall between £500 and £8,000. We include G99 application management in our installation service and provide transparent cost estimates before you commit.
No. It is illegal to connect a generating installation above the G98 threshold to the distribution network without G99 approval. Connecting without approval poses safety risks to network engineers and the public, can damage network equipment, and violates the Electricity Act. Your DNO can require disconnection of any unapproved installation and may pursue legal action. The G99 process exists to ensure the safety and stability of the electricity network. Systems below 50kW may qualify for the simpler G98 notification process.
G99 applications are rarely outright rejected. More commonly, the DNO will identify constraints and offer a connection subject to reinforcement works, which the applicant pays for. If the reinforcement costs are prohibitive, options include reducing the system size to avoid the constraint, accepting export limitation (the system generates but limits how much is exported to the grid), or installing a smaller system that qualifies under G98. We assess grid capacity early in the project planning stage to identify potential issues before you commit to the investment.
Export limitation is a technical solution where the solar system is fitted with an export limiter that restricts the amount of electricity exported to the grid, usually to zero or a defined kW threshold. This can resolve DNO concerns about network capacity without requiring expensive reinforcement works. The system still generates its full capacity, but any excess beyond what you consume on-site and the export limit is curtailed. For businesses with high self-consumption rates, export limitation has minimal impact on financial returns while avoiding significant grid connection costs.
A typical G99 application to UK Power Networks requires: the completed ENA application form; single-line diagram (SLD) of the proposed installation; site plan showing the installation location; inverter technical specifications and protection settings; import/export metering arrangements; proposed protection relay settings; and evidence of planning consent if required. For larger systems (over 1MW), a Power Systems Analysis (PSA) report may also be required. We prepare all documentation as part of our installation service.
Ofgem and National Grid Electricity System Operator implemented significant grid connection queue reforms in 2025, reducing the UK grid connection queue from 722 GW to 283 GW (a 61% reduction) by removing stale, speculative applications. For commercial solar applicants in Essex, this has reduced competition for UK Power Networks' Gate 2 capacity allocation (3,085 MW in the EPN area). Straightforward commercial solar applications under 1 MW are largely unaffected and continue to follow the standard 45-working-day assessment process.
Battery storage systems that discharge to the grid are treated as generating installations and require their own G99 application. If battery storage is installed as part of a solar-plus-storage system, both the solar and battery export capacity must be accounted for in a single application. Export-only-limited systems (where the battery never exports to the grid, only charges from solar or off-peak grid) may be treated differently. We assess the optimal configuration for your site to minimise G99 complexity and cost.
UK Power Networks and other DNOs operate a "First Ready, First Connected" principle for grid connections. This means applications that complete their technical requirements and accept their connection offer are given priority for energisation over applications still awaiting documentation or decisions. Submitting a complete, accurate G99 application early in the project — and accepting the connection offer promptly — is therefore important for keeping your project timeline on track.
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