G99 Application

A G99 application is the process by which a UK renewable energy installer requests approval from the local Distribution Network Operator (DNO) to connect a power generation system to the electricity distribution network. Engineering Recommendation G99 - published by the Energy Networks Association - sets out the technical standards that generating plant above 16A per phase must meet before connection. For installers of commercial solar PV, battery storage, and larger renewable generation systems, the G99 process is a mandatory step before commissioning. Without approval, a system above 16A per phase cannot legally export to the grid.

What the G99 Application Process Involves

The application requires technical documentation: a single-line diagram of the proposed installation, inverter and panel datasheets, protection relay settings, and the earthing arrangement. The installer typically submits on behalf of the system owner. Six DNOs cover different geographic regions in mainland UK: UK Power Networks (London and the South East), Northern Powergrid (Yorkshire and the North East), SP Energy Networks (Central Scotland and South Wales), Western Power Distribution (Wales, the Midlands, and the South West), Electricity North West (the North West), and Scottish and Southern Electricity Networks (northern Scotland and Central Southern England).

A typical G99 timeline for a commercial system up to 250kWp runs 8-16 weeks end to end. A pre-application enquiry (1-2 weeks) establishes feasibility and network capacity. The formal submission goes through a DNO technical review (4-8 weeks for systems above 17kWp), after which the DNO issues a connection offer specifying any export limit, connection charges, and technical conditions. Commissioning and witness testing - required in person by the DNO for systems above 50kWp - follows acceptance of the offer. Sites above 250kWp requiring capacity studies extend to 16-26 weeks. Sites needing network reinforcement can take 6-12 months.

Costs, Export Limits, and Common Complications

G99 connection charges vary by DNO and project size. Standard application fees range from £500 to £2,000. Witness testing for systems above 50kWp adds £500 to £1,500. Capacity studies for larger systems cost £2,000 to £8,000. Where network reinforcement is required, costs range from £15,000 to over £500,000. For a typical 100-500kWp commercial project, budget £3,000-£8,000 for DNO costs, excluding reinforcement.

The most commercially significant risk is an export limit lower than the system's nameplate capacity. If the DNO determines the local network cannot absorb full export, it caps the maximum. For sites with high self-consumption - manufacturing premises, data centers, busy hospitality sites - a reduced export limit has limited financial impact. For sites with low daytime occupancy - schools, weekend venues, seasonal operations - the inverter curtails generation rather than export beyond the limit, reducing annual yield and return on investment. Battery storage, sized to capture curtailed generation and shift it to higher-load periods, is the primary mitigation for export-constrained projects.

In Zigaflow, the G99 application can be tracked as a milestone within the installation job record - recording the submission date, DNO reference number, and target date for the connection offer. When the offer does not arrive within the expected window, the overdue milestone prompts the team to follow up with the DNO rather than let the application stall silently.