A G99 application is the formal approval a Distribution Network Operator (DNO) issues before any generating equipment above 3.68kW per phase can be connected to the UK electricity distribution network. It applies to commercial-scale solar PV, wind, battery storage, CHP and hybrid systems, and is split into four cumulative types (A to D) based on capacity and connection voltage.
Introduction
Almost every commercial-scale renewable energy project in the UK needs a G99 connection offer before it can be built. The application sits at the centre of the development timeline, determining technical viability, connection cost, and the conditions under which a project can export to the grid. This article explains what G99 is, who needs one, and how the application process works.
What is a G99 application?
A G99 application is a request to a DNO to connect generating equipment to the public electricity distribution network under Engineering Recommendation (EREC) G99, the standard published by the Energy Networks Association (ENA). G99 replaced G59 in April 2019 and is mandatory above the G98 micro-generation threshold (Energy Networks Association, 2025).
The Distribution Network Operator (DNO) is the regional company responsible for delivering electricity from the national transmission network to homes and businesses. There are six DNO groups operating 14 licensed areas across Great Britain: UK Power Networks, National Grid Electricity Distribution (NGED), SP Energy Networks, Northern Powergrid, Electricity North West, and Scottish and Southern Electricity Networks (SSEN).
G99 applies to solar PV, wind, battery storage, diesel and gas generators, CHP, and any hybrid system exporting above 3.68kW per phase (single-phase) or 11.04kW total (three-phase). Below those thresholds the lighter G98 "install then notify" process applies. G99 reverses this logic: apply first, install only after the connection offer is accepted (NGED Generation (G99), 2025).
Why G99 exists
G99 protects network stability, voltage quality, and worker safety. By requiring DNOs to assess every connection above the micro-generation threshold, it ensures generators do not destabilise local voltage, exceed thermal limits on cables and transformers, or create islanding risks during faults (Energy Networks Association, 2025).
The four G99 types
G99 splits generators into four cumulative categories based on Registered Capacity and connection voltage (ENA Distributed Generation Connection Guides, 2025):
| Type | Capacity | Voltage |
|---|---|---|
| Type A | Less than 1 MW | Below 110 kV |
| Type B | 1 MW to less than 10 MW | Below 110 kV |
| Type C | 10 MW to less than 50 MW | Below 110 kV |
| Type D | 50 MW and above | Typically at or above 110 kV |
Each type inherits the requirements of the categories below it. A Type D project must comply with the obligations of Types A, B and C as well as its own additional duties. The type determines the depth of compliance testing, witness requirements, and documentation needed, and is a primary driver of how complex the application becomes. Type A projects follow a streamlined compliance route (ENA G99 Type A Full Guide, 2025), while Types B to D face progressively heavier testing and witness obligations (ENA G99 Types B-D Full Guide, 2025).
The application process step-by-step
A typical G99 application follows six stages (NGED G99 Connection Procedures Guidance, 2025):
- Pre-application enquiry (optional but recommended). The developer asks the DNO for an informal view on capacity at the proposed connection point, often informed by a DNO heat map.
- Formal application. The developer submits the G99 form with site location, capacity, technology, single-line diagram, and equipment compliance certificates. Most DNOs accept applications via online portals (NGED Generation (G99), 2025) (Electricity North West EREC G99, 2025).
- DNO assessment. The DNO checks available capacity, identifies any reinforcement needed, and produces a quote. The statutory 45-working-day clock starts here.
- Connection offer. The DNO issues a written offer specifying connection cost, point of connection, any reinforcement charges, and an expiry date, typically valid for three months.
- Acceptance and payment. The developer accepts the offer, pays the connection charge, and signs the connection agreement.
- Installation, commissioning, energisation. The site is built, the DNO witnesses commissioning tests for Type B and above, and the connection is energised.
What information the application requires
A complete G99 application typically requires: site address and grid reference, technology type and manufacturer, Registered Capacity, single-line electrical diagram, protection settings, type-test certificates demonstrating EREC G99 compliance, and details of any energy storage or export limiting equipment (SP Energy Networks Distributed Generation Connection Guide, 2024). Missing or inconsistent documentation is one of the most common causes of delay.
Indicative costs in 2026
Assessment fees vary widely by DNO and project complexity, from a few hundred pounds for simple LV applications to several thousand pounds for larger HV schemes. Final connection costs range from tens of thousands of pounds to many millions where major reinforcement is required.
Reinforcement costs, the charges levied where the existing network must be upgraded to accommodate a new connection, can be more significant than the connection charge itself and are the single largest source of cost surprise at the offer stage. Under Ofgem's Significant Code Review, the cost allocation between developer and DNO for reinforcement has shifted over recent years, but developer exposure remains material for projects in constrained parts of the network (NGED G99 Connection Procedures Guidance, 2025).
UK regulatory context
G99 sits within a layered UK regulatory framework. The ENA publishes the engineering standards (Energy Networks Association, 2025) (ENA Distributed Generation Connection Guides, 2025), Ofgem regulates the DNOs through the RIIO-ED2 price control, and the National Energy System Operator (NESO) coordinates the interface between distribution and transmission. The standard is mandatory and applies uniformly across England, Wales and Scotland, although individual DNOs publish their own application portals and supporting guidance.
The Department for Energy Security and Net Zero (DESNZ) target of clean power by 2030 depends on connecting a significant volume of new distribution-connected generation, much of it solar PV, onshore wind, and battery storage. G99 is the procedural gateway for that capacity.
Why this matters for site selection
Most delays in the G99 process originate before the formal application is even submitted. Sites chosen without adequate grid headroom, sites that sit on the wrong side of a constrained transformer, or sites that trigger reinforcement at a higher voltage tier all result in slow, expensive, or rejected connections. Pre-application screening is the single highest-leverage activity in the development cycle.
Feasibly compresses this screening work by pulling live data from all UK DNOs alongside planning and geospatial datasets, accessible via natural language. For commercial developers, this means a better-targeted G99 application with a higher chance of an acceptable offer. For community energy groups, it means the feasibility check that historically priced them out becomes affordable.
Conclusion
A G99 application is the formal route by which any generator above 3.68kW per phase joins the UK distribution network. Understanding which of the four types applies, what documentation the DNO requires, and where reinforcement costs are likely to bite is essential preparation. Developers who pre-screen sites thoroughly before submitting their G99 form move through the process faster, pay less in unexpected charges, and avoid the most common reasons for connection offers being delayed or refused.