G99 Connection Overview
G99 (EREC G99) governs the connection of generation equipment to UK distribution networks. Projects are classified as Type C (10-50MW, below 110kV) or Type D (≥50MW or ≥110kV) based on capacity and connection voltage.
Despite the different classifications, the technical study requirements are the same. G99 Section 13 applies to both Type C and Type D, specifying identical requirements for harmonics, voltage fluctuation, reactive capability, and dynamic performance.
The differences between Type C and Type D are primarily administrative: the commissioning process (Type D has a staged approach) and the loss of mains protection methodology (intertripping rather than RoCoF for ≥50MW installations).
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Type Classification
Type C
10MW to <50MW, connecting below 110kV
- • Typical voltages: 11kV, 33kV, 66kV
- • Direct path to Final Operational Notification
- • RoCoF loss of mains protection acceptable
Type D
≥50MW OR connecting at ≥110kV
- • Typical voltages: 33kV, 66kV, 132kV+
- • Staged commissioning: EON → ION → FON
- • Intertripping typically required for LoM
Key point: The technical studies are identical for both Type C and Type D. G99 Section 13 applies to both classifications.
Study Requirements
Our packages include all G99 mandatory studies plus the additional analysis needed to complete the ICP design and DNO submission.
G99 Requirements
Mandatory studies specified in G99 Section 13:
Additional Design Studies
Required for ICP design and equipment specification:
Technologies We Support
Solar PV
Ground-mount and rooftop installations at distribution and transmission voltage
Battery Storage
Grid-connected BESS from 10MW to 100MW+
Wind
Onshore wind farms at distribution and transmission level
Hybrid Sites
Combined generation and storage installations
Connection Voltage Levels
Smaller Type C projects up to ~5MW
Most common for 5-50MW projects
Larger projects approaching 50MW+
Type D by voltage, includes transformer protection
Frequently Asked Questions
What is the difference between Type C and Type D?
The difference is primarily administrative, not technical. Type C applies to projects 10-50MW connecting below 110kV. Type D applies to projects ≥50MW OR connecting at ≥110kV. The technical study requirements under G99 are the same for both—the main differences are the commissioning process (Type D has a staged EON→ION→FON process) and loss of mains protection approach.
Are the studies different for Type C vs Type D?
No. G99 Section 13 covers both Type C and Type D with identical technical requirements. The only technical difference is a slightly more demanding fault ride-through voltage curve for connections at 110kV or above. All other study requirements—harmonics, P28, reactive capability, dynamic studies—are the same.
When is TSO/Grid Code compliance required?
TSO involvement (NGESO) is triggered by system location and impact, not by Type classification. Projects embedded in distribution networks that affect the transmission system may require Grid Code compliance regardless of whether they are Type C or D. We assess this on a project-by-project basis.
What voltage levels do you cover?
We deliver G99 packages for all distribution and transmission voltage levels: 11kV, 33kV, 66kV, 132kV, and above. The study scope is consistent regardless of voltage—the main difference is that higher voltage connections typically involve transformer protection studies.
How many rounds of revisions are included?
We work with you until DNO approval, not a fixed number of iterations. If the DNO raises comments on our reports or requests clarification, we address them at no additional cost—provided the project scope and design haven't changed. We don't limit you to "one set of consolidated comments" like some consultants.
What happens if a study shows non-compliance?
We identify the issue and recommend solutions—whether that's adjusting inverter settings, adding reactive compensation, or specifying mitigation equipment like harmonic filters or pre-insertion resistors. If additional equipment design is needed, we provide a variation quote for that specific scope. The original study itself isn't charged again.
What if the project design changes after studies have started?
Minor updates (cable lengths, transformer tap ranges) are absorbed within the project. Material changes—like capacity increases, additional feeders, or equipment substitutions—may require study re-runs. We discuss the impact and agree any variation before proceeding.
Do you handle DNO correspondence directly?
Yes. We respond to technical queries, submit SAF/PGMD documentation, and address DNO comments on your behalf. You're copied on correspondence but don't need to interpret or relay technical questions.
Get Your G99 Quote
Send us your connection offer and project details. We'll provide a scope and fee proposal covering all required studies.