Grid Connection Approval for Solar PV Systems in the UK

Grid Connection Approval for Solar PV Systems in the UK: The Complete EPC Contractor Guide

The UK installed over 1.7 GW of new solar PV capacity in 2023 alone, yet grid connection approval remains one of the most common causes of project delay across the country. For EPC contractors managing commercial and industrial solar PV installations, understanding the grid connection approval UK solar process is not optional. It is the single most critical pathway between a signed contract and a live, revenue-generating system. Delays at the grid connection stage can push commissioning dates back by months and, in some cases, collapse projects entirely. This guide covers everything EPC contractors must know to navigate the UK’s grid connection framework with confidence and precision.

Understanding the UK Solar PV Grid Connection Framework

The UK grid connection process for solar PV systems is governed primarily by two engineering recommendations: G98 and G99. These standards, published by the Energy Networks Association, define the technical requirements and procedural obligations for connecting generation equipment to the distribution network. Before any EPC contractor submits a DNO application solar PV, understanding which standard applies to the project in question is the essential first step.

The distribution network operator solar connection process sits at the heart of nearly all commercial solar installations in the UK. DNOs are the licensed companies responsible for operating and maintaining the electricity distribution networks in specific regions. Examples include UK Power Networks, Western Power Distribution (now National Grid Electricity Distribution), SP Energy Networks, Northern Powergrid, and Electricity North West. Each DNO operates within a regulatory framework set by Ofgem but has its own procedural nuances, timescale expectations, and technical preferences that experienced EPC contractors learn to navigate over time.

G98 vs G99 Solar: The 16A Per Phase Threshold

The distinction between G98 vs G99 solar connections comes down to a single critical threshold: 16 amperes per phase. For generation equipment with an output at or below 16A per phase (equivalent to approximately 3.68 kW on a single-phase supply or 11 kW on a three-phase supply), the G98 notification route applies. This is a simplified process that does not require prior approval from the DNO. The installer simply notifies the DNO within 28 days of energisation using the G98 notification form and confirms that the installed equipment meets the standard’s technical requirements.

For anything above the 16A per phase threshold, the G99 grid connection route applies. This is a formal application process that requires prior written approval from the DNO before the system can be energised. The G99 route introduces a multi-stage review process, including technical documentation assessment, potential engineering studies, and formal offer acceptance. For the vast majority of commercial rooftop and ground-mounted solar PV projects handled by EPC contractors, G99 is the applicable standard.

There is an important nuance that catches less experienced contractors off guard. Even if individual inverters fall below the 16A threshold, if the combined export capacity of the entire installation exceeds 16A per phase at the point of connection, G99 applies to the whole installation. This is a common scenario with multi-inverter commercial rooftop systems where each inverter appears small but the aggregate output triggers the G99 requirement.

The Solar PV Grid Connection Process: End to End for EPC Contractors

The solar PV grid connection process under G99 is structured across several distinct stages. Each stage has its own documentation requirements, decision points, and typical timescales. Understanding this sequence in detail allows EPC contractors to programme projects realistically and avoid the costly assumption that grid connection approval is a formality that can be sorted out after construction begins.

Stage 1: UK Solar Feasibility Study and Pre-Application Enquiry

Before submitting a formal G99 application, the single most valuable action an EPC contractor can take is commissioning a UK solar feasibility study and submitting a pre-application enquiry to the relevant DNO. This step is not mandatory under the G99 process, but it is strongly recommended for any project above 50 kW.

The pre-application enquiry communicates the proposed connection point, the system’s anticipated generation capacity, the export limit (if applicable), and the proposed connection voltage. The DNO uses this information to run initial network capacity checks and return a feasibility response indicating whether the local network can accommodate the proposed generation without constraint. Typical timescales for a feasibility response range from 4 to 8 weeks, though some DNOs are currently experiencing longer response times due to the volume of applications driven by the solar surge.

The intelligence gathered from the feasibility stage is invaluable. On one project involving a 750 kW rooftop installation on a logistics facility in the East Midlands, the pre-application response revealed that the local 11 kV network had only 400 kW of headroom before thermal limits were breached. The EPC contractor used this information to redesign the export arrangement with an active export limitation system, avoiding a formal rejection and a potentially fatal programme delay. Without the feasibility study, that project would have submitted a full G99 application only to receive a refusal several months later.

Stage 2: Formal G99 Application Submission

Once the feasibility response indicates that a connection is achievable, the formal G99 application is submitted to the DNO. This submission must include a defined set of solar grid connection documents that vary slightly by DNO but follow a broadly consistent structure. The application form itself captures project details, proposed connection point, generation capacity, inverter technology, export limitation arrangements, and protection scheme details.

DNO review timescales at this stage are regulated by Ofgem. For simpler projects where no network reinforcement is required, DNOs are expected to issue an offer within 65 working days. For more complex projects requiring detailed technical studies, this timescale can extend significantly. Some DNOs issue interim holding responses acknowledging receipt and indicating when a substantive response will follow.

Stage 3: Offer Acceptance and Connection Agreement

When the DNO issues its connection offer, it will specify the approved connection capacity, any export limitation requirements, connection voltage, protection requirements, metering arrangements, and the connection charges associated with any network reinforcement works. The EPC contractor or project owner must formally accept the offer within the deadline stated (typically 30 to 90 days) and pay any associated connection charges to secure the agreement.

EPC contractors should review the offer in detail before acceptance. Connection charges for projects requiring network reinforcement can be substantial, and the scope of reinforcement works (which are carried out by the DNO at the applicant’s cost) can affect project viability. If the offer conditions are materially different from what the feasibility stage indicated, it is worth engaging directly with the DNO’s connections team to understand the technical basis for any changes before accepting.

Stage 4: Technical Design Submission and DNO Approval

After offer acceptance, the EPC contractor must submit a detailed technical design package for the DNO’s engineering review. This is the most technically demanding stage of the EPC contractor grid approval process and where many submissions falter due to incomplete or non-compliant documentation. The DNO’s engineers will assess the proposed protection scheme, inverter settings, export control methodology, and electrical schematics against the requirements of G99 and their own network design standards.

Approval at this stage is required before any energisation can take place. DNOs will not issue commissioning approval without signed-off technical documentation. Timescales for technical design approval typically range from 4 to 12 weeks depending on complexity and the DNO’s current workload.

Stage 5: Commissioning and Final Energisation Sign-Off

The final stage of the solar PV grid connection process is commissioning and energisation. This requires a witnessed commissioning test (in some cases) and the submission of commissioning test results to the DNO confirming that the protection relays and inverter settings match the approved technical design. Once the DNO issues its energisation consent, the system can be connected to the grid and export can begin.

Post-energisation, the project owner is required to maintain records of the connection agreement, protection settings, and commissioning results. Annual testing of protection relays is typically required under the connection agreement terms.

Key Technical Documents Required for a Successful Grid Connection Submission

The quality of solar grid connection documents submitted to the DNO directly determines how smoothly the application progresses. Incomplete, inconsistent, or poorly produced documentation is one of the primary reasons for application delays and rejections. The following documents form the core of a compliant G99 submission package.

Single-Line Diagrams Produced in AutoCAD

The single-line diagram (SLD) is the most scrutinised document in any grid connection package. DNO engineers use the SLD to understand the proposed electrical architecture, protection scheme, metering arrangement, and export control configuration at a glance. An SLD produced to professional standards in AutoCAD communicates competence and makes the review engineer’s job straightforward, which invariably accelerates approval.

The SLD must show the generation source (inverters), AC cabling arrangement, protection devices (overcurrent, earth fault, loss-of-mains), metering point, isolation points, export limitation hardware (if applicable), and the point of connection to the DNO network. Any discrepancy between the SLD and other submitted documents (such as protection settings sheets or equipment data sheets) will result in a request for clarification and delay the review process.

Protection Relay Settings and Coordination Study

G99 requires that generation equipment be protected by a loss-of-mains (LoM) protection function, among other requirements. The protection relay settings must be documented in a settings schedule that demonstrates compliance with the approved DNO interface protection requirements. For larger projects, a protection coordination study may be required to demonstrate that the proposed protection scheme is correctly graded with the DNO’s own network protection and will not cause spurious trips or, more critically, fail to disconnect generation in fault conditions.

Protection settings are highly specific to the inverter technology, connection voltage, and DNO network characteristics. Using generic or template settings documents without verifying their applicability to the specific project is a common mistake that results in requests for revision.

PVsyst Energy Yield Reports

A PVsyst simulation report serves multiple purposes in a grid connection package. It provides the DNO with verified data on the system’s expected annual generation, peak output, and performance ratio. This data underpins the network impact assessment. The PVsyst report also validates the system design by confirming that the proposed inverter and module configuration is technically coherent.

For EPC contractors, the PVsyst report is also a contractual document that establishes the performance baseline against which the installed system will be measured. Ensuring that the simulation inputs (meteorological data source, shading analysis, system losses, degradation rates) are accurately calibrated to the specific site is essential. A PVsyst report produced with default loss assumptions rather than site-specific inputs may underestimate or overestimate yield and misrepresent the system’s export profile to the DNO.

For a deeper look at how solar system design informs grid connection documentation, the guide to how a PV solar system is designed provides valuable context on the relationship between design decisions and grid approval requirements.

Common Grid Connection Rejection Reasons and How to Avoid Them

Understanding why applications fail is as important as understanding the application process itself. The following are the most frequently encountered technical rejection grounds in the UK solar market, along with the pre-application engineering approaches that de-risk submissions.

Thermal Constraints on the Distribution Network

Thermal constraints arise when the existing network infrastructure (cables, transformers, switchgear) does not have sufficient spare capacity to carry the additional current that would be generated by the proposed solar installation during peak output periods. DNO feasibility assessments model the thermal loading on each network component and flag where proposed generation would push current levels beyond equipment ratings.

The solution is not always to reduce the system size. Export limitation systems, which cap the maximum power fed into the grid at a defined level below the system’s full generation capacity, can resolve thermal constraint issues without compromising the amount of self-consumed energy or on-site battery charging capacity. For EPC contractors designing systems for commercial clients with high daytime consumption, this is often the optimal approach.

Fault Level Issues at the Point of Connection

Solar PV inverters contribute to fault current under network fault conditions. If the existing network infrastructure at the proposed point of connection is already operating close to its rated fault level, the additional fault current contribution from a new solar installation can breach the switchgear’s rated breaking capacity. This is a common constraint at 11 kV connection points in areas with existing high levels of embedded generation.

Pre-application engineering studies that include fault level analysis allow the design team to identify this risk early. In some cases, connecting at a higher voltage point (for example, moving from an LV to an 11 kV connection) can resolve fault level constraints by distributing the fault current contribution across a more robust section of the network.

Voltage Rise Calculations

Voltage rise is one of the most technically nuanced rejection grounds. When solar generation exceeds local consumption, current flows back towards the grid, and under Ohm’s law, this causes the network voltage to rise above the nominal level. UK grid regulations require that the network voltage at any point does not exceed defined statutory limits (typically plus 6% for LV networks under EREC P2 and G99).

DNOs model voltage rise using power flow analysis tools and will reject applications where the proposed generation would cause voltage to exceed limits. The pre-application mitigation options include reactive power control (where inverters absorb reactive power to counteract voltage rise), export limitation, or connection at a higher voltage level where the impedance characteristics are more favourable.

How Lion Solar Solutions Prepares Grid Connection Packages for EPC Contractors

For EPC contractors who need to deliver grid connection approval as part of a larger project scope, the burden of producing a technically complete, DNO-compliant submission package is significant. Lion Solar Solutions supports EPC contractors by preparing integrated grid connection document sets that combine all required technical elements into a single, submission-ready package.

The approach begins with a thorough review of the project’s proposed design, site location, and DNO connection point. PVsyst simulations are run using site-specific meteorological data and calibrated shading analysis to produce accurate yield and peak output figures. AutoCAD single-line diagrams are produced to professional standards, reflecting the actual proposed electrical architecture rather than generic templates. Protection relay settings schedules are prepared in accordance with the specific DNO’s interface protection requirements and the selected inverter manufacturer’s compliance documentation.

Where the project involves structural considerations (such as rooftop ballasted arrays where load data is critical to both structural approval and grid connection documentation), the load data is integrated into the submission package alongside the electrical schematics. This is particularly relevant for projects where the structural assessment and the grid connection application are submitted concurrently to reduce the overall programme timeline.

EPC contractors working on projects that require early-stage design coordination will find the solar design preparation checklist a practical tool for ensuring that all necessary inputs are gathered before the grid connection documentation process begins. Having the correct site survey data, network connection point details, and client consumption data available from the outset avoids the mid-process information gaps that slow down application preparation.

The output of Lion Solar Solutions’ grid connection package preparation service is a document set that covers the G99 application form, the single-line diagram, the protection settings schedule, the PVsyst simulation report, inverter compliance documentation, and export limitation scheme details where applicable. The package is structured to align with the specific DNO’s submission preferences, reducing the likelihood of requests for additional information that extend the review period.

The Role of National Grid ESO in UK Solar PV Projects

For the majority of EPC contractors working on commercial and industrial solar PV projects, the National Grid ESO solar connection process is not directly relevant. National Grid ESO (Electricity System Operator) manages the high-voltage transmission network in Great Britain, and solar PV projects typically connect directly to it only when capacity exceeds approximately 50 MW. Below this threshold, connections are handled entirely through the relevant DNO.

However, National Grid ESO’s work is indirectly significant to all solar developers. The ESO publishes Future Energy Scenarios and network development roadmaps that inform DNO investment plans. Grid reinforcement programmes undertaken by DNOs in response to ESO’s strategic planning directly affect the availability of headroom at distribution connection points. Staying informed about ESO publications gives EPC contractors and their clients a forward view of where grid capacity constraints are likely to ease or tighten over the coming years, which can influence site selection and investment timing decisions.

Additionally, National Grid ESO operates the Balancing Mechanism and sets certain technical requirements for generators above defined capacity thresholds. For solar-plus-storage projects that cross into mandatory frequency response territory, understanding the ESO’s requirements is essential even where the physical grid connection is managed through a DNO.

Programme Planning: Realistic Timescales for EPC Contractors

One of the most persistent sources of project programme errors in the UK solar sector is the underestimation of grid connection timescales. EPC contractors who plan construction programmes without accounting for the full G99 approval timeline regularly find themselves with installed systems that cannot be energised because grid approval has not yet been received.

The following represents a realistic programme framework for a typical commercial solar PV project connecting under G99:

1. Pre-application feasibility enquiry submission and response: 4 to 8 weeks
2. Preparation of formal G99 application documentation: 2 to 4 weeks (dependent on design complexity)
3. DNO formal application review and connection offer: 8 to 13 weeks (regulated timescale for standard projects)
4. Offer acceptance and connection agreement execution: 1 to 4 weeks
5. Technical design submission and DNO engineering approval: 4 to 12 weeks
6. Commissioning, testing, and energisation consent: 2 to 4 weeks

In aggregate, a commercial solar PV project can expect the grid connection process from initial feasibility enquiry to energisation to take a minimum of 6 months and potentially 12 to 18 months where network reinforcement is required. EPC contractors should initiate the grid connection process as early as possible in the project lifecycle, ideally at the feasibility and design stage rather than after procurement or construction has commenced.

Frequently Asked Questions About Grid Connection Approval for Solar PV in the UK

Conclusion: Grid Connection Approval as a Project-Critical Discipline

Grid connection approval is not an administrative formality sitting at the end of the solar PV project lifecycle. It is a project-critical technical discipline that must be engaged from the earliest stages of feasibility and design. For EPC contractors operating in the UK solar market, the ability to manage the grid connection approval UK solar process competently is a genuine competitive differentiator. Contractors who initiate the DNO application process early, produce technically rigorous documentation, and conduct pre-application engineering studies consistently deliver projects on programme and within budget. Those who treat grid connection as an afterthought consistently absorb delays, cost overruns, and in the worst cases, project failures.

The G98 versus G99 threshold, the multi-stage DNO application process, the technical documentation requirements, and the common rejection grounds explored in this guide represent the core knowledge set that separates expert EPC delivery from reactive problem-solving. Whether a contractor is managing a 100 kW rooftop installation or a multi-MW ground-mounted array, the fundamental discipline of the grid connection process remains consistent.

For EPC contractors who want to ensure that their grid connection submissions are technically complete and DNO-ready from the outset, Lion Solar Solutions provides end-to-end grid connection package preparation services integrating PVsyst simulation outputs, AutoCAD schematics, and protection documentation into a single coherent submission. Starting with accurate design inputs makes this possible. Reviewing the solar design preparation checklist and understanding how a PV solar system is designed provides the foundation on which every successful grid connection application is built.

Heval Arcan