If you're developing a solar farm or large-scale renewable energy project in the UK, you'll need to navigate the G99 grid connection process. This guide explains everything you need to know about G99 applications, from initial feasibility to final energisation - including the queue management reforms that are reshaping how projects get connected.

What Is a G99 Application?

A G99 application is the formal process for connecting power-generating equipment over 3.68kW per phase to the UK electricity distribution network. G99 (Engineering Recommendation EREC G99) replaced the older G59 standard in April 2019 and applies to all large-scale generation including solar farms, wind turbines, and battery storage systems. Every solar farm in the UK requires G99 approval from the local Distribution Network Operator (DNO) before installation can begin.

You must submit a G99 application if your project meets any of the following criteria:

• Capacity over 3.68kW per phase (single-phase) or over 11.04kW (three-phase)
• Any commercial solar installation - even with zero export, the installed capacity dictates the application type
• Non-type tested equipment - common for large-scale solar inverters

The key difference from smaller installations is that G99 requires formal DNO (Distribution Network Operator) approval before you can install. You cannot simply install and notify as you would with a residential system.

G99 vs G98: Which Do You Need?

The choice between G99 and G98 depends primarily on your system size:

For solar farms, there's no question - you'll need G99. Even a modest 50kW commercial rooftop system requires G99 approval.

For a more detailed breakdown of the differences, including Fast Track options and common scenarios, see our dedicated G98 vs G99 comparison guide.

What Is the G99 Application Process?

The G99 application process has five phases: feasibility study (10-20 working days), formal application via Standard Application Form (45-65 working days for DNO response), connection offer acceptance (30-90 days to decide), construction and commissioning (6-24 months), and operational notification. The total process from initial enquiry to energisation typically takes 2-5 years for solar farm projects.

Phase 1: Feasibility & Budget Estimate (Optional but Recommended)

• Action: Apply for a "Budget Estimate" or "Feasibility Study" from your local DNO
• Outcome: A rough cost estimate (±50%) and indication of available grid capacity
• Timeline: 10-20 working days
• Cost: Usually free or minimal fee

This step is crucial for solar farms. It tells you whether there's grid capacity in your area before you invest in detailed technical designs. Many projects discover at this stage that local infrastructure is constrained.

Phase 2: Formal Application

• Action: Submit the Standard Application Form (SAF) to the local DNO
• Requirement: You must demonstrate "Land Rights" with a Letter of Authority from the landowner
• Timeline: DNO has 45-65 working days (approximately 3 months) to issue a Connection Offer

Phase 3: Connection Offer & Acceptance

• Action: DNO issues a formal "Connection Offer" detailing costs, connection date, and required works
• Decision: You typically have 30-90 days to accept and pay the deposit
• Important: New offers include "Queue Management Milestones" - miss these and you lose your place

Phase 4: Construction & Commissioning

• Action: Build the solar farm (DNO may need to complete reinforcement works first)
• Timeline: 6-24 months depending on project size
• Milestone: G99 Witness Testing - DNO engineers visit site to witness protection tests

Phase 5: Operational Notification

• Action: Submit Form B3 (final commissioning forms)
• Outcome: DNO issues "Final Operational Notification" (FON) - you are now live

What Documents Do You Need for a G99 Application?

A G99 application requires three essential documents: a Single Line Diagram (SLD) showing the electrical schematic, a Letter of Authority signed by the landowner, and evidence of planning status. Additional technical data includes inverter datasheets, fault level analysis, protection settings, and proposed cable routes. For solar farm projects, prepare the following:

Essential Documents

• Single Line Diagram (SLD): Professional electrical schematic showing point of connection, protection relays, and isolation points
• Letter of Authority: Signed by landowner granting developer permission to apply
• Planning Status: Evidence of planning application or pre-application advice (now critical for queue position)

Technical Data Required

• Inverter datasheets with PQ diagrams and fault ride-through capabilities
• Maximum Export Capacity (MEC) required
• Earthing arrangements
• Protection settings and relay specifications
• Proposed cable routes and lengths

How Much Does a G99 Application Cost? (2026 Rates)

G99 application costs have two components: assessment fees (£500-£8,000+, non-refundable) and connection charges (£50,000-£2,000,000+). Assessment fees cover the DNO's design work to produce a Connection Offer. Connection charges cover the physical infrastructure — cables, switchgear, and any substation reinforcement required.

A. Assessment & Design Fees

Most DNOs charge upfront just to process the application:

• HV (High Voltage) Connection: £500 - £2,500
• EHV (Extra High Voltage) / 33kV+: £3,000 - £8,000+

Note: These fees are non-refundable even if the connection cost is too high to proceed.

B. Witness Testing Fees

• Standard Rate: Approximately £957 + VAT per visit
• Rates vary slightly by DNO (UK Power Networks, SSEN, National Grid, etc.)

C. Connection Charges (The Major Cost)

• Reinforcement: If the local substation needs upgrading, you may pay a share
• Sole Use Assets: You pay 100% for assets installed just for your site
• Typical Solar Farm Cost: £50,000 to £2,000,000+ depending on distance to substation and voltage level

What Is the UK Grid Connection Queue?

The UK grid connection queue currently has over 500GW of projects waiting to connect, with some areas showing connection dates of 2030-2036. The queue is being reformed from a "first-come, first-served" system to a "First Ready, First Connected" model that prioritises projects with planning permission and confirmed land rights. Projects that cannot demonstrate progress are being removed to free capacity for viable developments.

The Current Crisis

There's currently a backlog of over 500GW of projects waiting to connect to the grid. Many areas have connection dates of 2030-2036. This backlog is largely caused by speculative applications from projects that never intended to build.

Queue Management Reforms

The new rules are designed to clear out "zombie projects" and prioritise viable developments:

• "First-Ready, First-Connected": The old "first-come, first-served" queue is being replaced. You can no longer hold a queue position without demonstrating progress.
• Gate 2 Process: To secure a firm connection date, projects must pass "Gate 2" criteria, which typically requires having Land Rights and Planning Permission (or advanced progress).
• Strict Milestones: New connection offers include "User Progression Milestones." Missing these results in automatic termination of your grid offer.

Why Do G99 Applications Get Rejected?

G99 applications are most commonly rejected for five reasons: thermal constraints (local network at capacity), reverse power flow issues at the Grid Supply Point, incomplete technical documentation, speculative applications without genuine land rights, and non-compliant inverter equipment. Understanding these failure modes helps prepare a stronger submission:

• "Thermal Constraints": The local cables and transformers are at capacity. The DNO cannot accept more export without significant (often millions of pounds) upgrades.
• "Reverse Power Flow": Sending power up to the transmission grid (National Grid) is blocked at the Grid Supply Point (GSP).
• Incomplete Forms: Missing single line diagrams or incorrectly specified inverter protection settings.
• Speculative Application: Failure to provide landowner authority or evidence of genuine project intent.
• Non-compliant Equipment: Inverters that don't meet G99 requirements (fault ride-through, protection settings).

How Do You Get a G99 Application Approved?

1. Secure Land First: Never apply without a signed Letter of Authority from the landowner. DNOs now rigorously verify land rights.
2. Check DNO Heat Maps: Most DNOs publish online capacity maps (e.g., UKPN Open Data Portal) showing red/green areas. Target areas with available capacity.
3. Hire a Specialist: For anything over 50kW, the technical complexity typically requires a specialist electrical engineer.
4. Consider Flexible Connections: You may get connected sooner by agreeing to "Active Network Management" (ANM), where the DNO can remotely curtail your output during rare peak congestion times.
5. Progress Planning Early: With the new "First Ready, First Connected" rules, having planning permission significantly improves your queue position.
6. Get a Budget Estimate First: Before investing in detailed designs, get a feasibility study to confirm grid availability.

Frequently Asked Questions