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

G99 by DNO: Fees, Timelines & Quirks

Each DNO handles G99 applications differently. Official guides won't tell you this, but turnaround times, admin fees, and capacity vary significantly. Here's what we've found from real-world data and published DNO documents:

The 2026 Grid Queue Crisis (& Reform)

The UK grid queue has undergone the biggest reform in its history. The pre-reform queue held 722GW of projects — four times what the UK needs to hit its 2030 clean energy targets. Under the new "First Ready, First Connected" system, that's been slashed to 283GW — a 61% reduction. If your project is viable, this is the best news in years.

The Numbers Behind the Reform

Gate 2 Timeline: When Offers Are Being Issued

Gate 2 is the mechanism that replaced first-come-first-served. To secure a firm connection date, your project must pass Gate 2 criteria — land rights + planning permission (or advanced progress). Offers are being issued now:

• Transmission offers (Phase 1): Mid-May to mid-September 2026
• Distribution offers (Phase 1): Early July to mid-November 2026
• Transmission offers (Phase 2): Early September 2026 to mid-January 2027
• Distribution offers (Phase 2): Mid-October 2026 to mid-March 2027
• Next application window: Q2 2026 at earliest (delayed from original timeline)

The Data Centre Problem

A new threat to the queue: data centre demand surged from 41GW (November 2024) to 125GW (June 2025). Around 50GW of data centres now sit in the connection queue — exceeding the UK's entire peak electricity demand of 45GW. The government has designated "AI Growth Zones" as strategically important, giving them queue priority. This directly competes with renewable energy projects for connection dates.

What This Means for Your Project

• 8 milestones now track progress from planning consent through construction — miss one and you lose your place
• 90 days to respond to transmission connection offers (non-negotiable)
• Projects with planning permission + secured land are being fast-tracked through Gate 2
• Projects without both are being held in the Gate 1 waiting list or terminated

Why Do G99 Applications Get Rejected?

G99 applications are rejected for five main reasons. The first two are technical constraints you can check before applying. The last three are preventable errors that waste months:

4 Options After G99 Rejection (Ranked by Speed & Cost)

A G99 rejection isn't the end. Most guides bury this information, but you have four clear paths forward — and one of them is often the smartest option even before you get rejected:

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