G98 vs G99 for Farm Solar: DNO Grid Connection Explained Simply

Every farm solar installation in the UK must be connected to the grid under either Engineering Recommendation G98 or G99. The distinction matters enormously: G98 connections are straightforward self-notification; G99 applications involve your DNO, can take months, and sometimes require grid reinforcement at significant cost. Understanding which applies to your farm — and how to navigate the process — is one of the most important decisions in your project timeline.

G98 vs G99: the key difference

G98 covers generating units up to 16A per phase (approximately 3.68 kW single-phase, 11.04 kW three-phase). G99 covers everything above that threshold, which includes the vast majority of farm solar installations. Almost all commercial farm solar systems — from a 30 kWp rooftop to a 2 MWp ground array — fall under G99.

G98: notification only

If your installation genuinely falls under the G98 threshold (rare for farms), you simply notify your DNO 28 days before energisation. No prior approval is needed. The DNO may carry out a check but cannot refuse connection for a compliant installation.

G99: application and approval required

G99 requires you to submit a formal application to your DNO with technical details of the generating plant, protection relay settings, and export management arrangements. The DNO then assesses the local network capacity and issues either an unconditional offer or a conditional offer requiring reinforcement.

How long does a G99 application take?

Ofgem requires DNOs to issue a connection offer within 65 business days of receiving a complete application. In practice, this varies widely by DNO and local network congestion. UKPN (South East) currently averages 35–50 days. Northern Powergrid has been running closer to 65 days on upland networks. NGED (South West/Midlands) is variable — urban substation areas are quick; rural radial networks can exceed the 65-day target.

What slows G99 applications down

Incomplete applications are the biggest cause of delay — missing protection relay details or incomplete site plans. Constrained 11 kV networks in rural areas require load flow studies that take time. And solar projects are competing with EV charger and wind applications in the same queue.

Export limitation and G99 fast-track

If you are willing to accept a zero-export or limited-export arrangement, most DNOs now offer a significantly faster “flexible connection” route. You install an active export control device that caps what you push to the grid. In return, the DNO processes your application in 20–30 days without a full network study. For farm sites where self-consumption exceeds 70% of generation, this is often the right choice.

Grid reinforcement: the cost surprise

If your local network is already at or near capacity, your DNO will quote reinforcement costs as part of the connection offer. These costs can range from a few thousand pounds (new service cable) to £100,000+ (new transformer or 11 kV line extension). Understanding your local network situation before committing to a system size can save significant time and money.

Conclusion

G99 is not something to be afraid of — it is a well-understood process that our project team navigates on every commercial installation. The key is to commission a pre-application grid study, submit a complete application first time, and consider zero-export limitation if your farm has high self-consumption.

Related reading

• UKPN Grid Connection Guide — UKPN-specific G99 process.
• Northern Powergrid Guide — Northern Powergrid G99 application process.
• NGED Grid Connection Guide — NGED (South West and Midlands) connection guide.
• Installation Process — Full timeline from survey to energisation.

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