What Are G99 and G100 Applications? A Complete Guide for Commercial Solar

If you are planning a commercial solar installation in the UK, two acronyms will appear early in every conversation with your installer: G99 and G100. These are the engineering standards that govern how your solar system connects to the local electricity distribution network, and getting them right is the single biggest factor determining whether your project proceeds smoothly or gets stuck in administrative limbo for months.

G99 is the formal application to connect generation equipment to the distribution network. It is required for any system with a capacity above 3.68 kW per phase — which covers essentially every commercial installation. The G99 process involves submitting detailed technical specifications of your proposed system to your local Distribution Network Operator (DNO), who then assesses whether the local grid has sufficient capacity to accept your generation without causing voltage issues or overloading transformers.

The timeline for G99 approval varies significantly by region and network conditions. In areas with strong grid infrastructure and low existing generation density, approvals can come through in four to six weeks. In areas where the local substation is nearing capacity — increasingly common in industrial estates with multiple solar installations — the DNO may require network reinforcement before granting approval. This can extend timelines to twelve weeks or more and may introduce additional costs if the reinforcement is chargeable to the applicant. Early engagement with your DNO during the feasibility stage is the most effective way to avoid surprises.

G100 is a separate but related standard that governs export limitation schemes. When a DNO determines that the local network cannot accept the full export capacity of your proposed system, rather than refusing the connection outright, they may offer approval under G100 conditions. This means your system must include an export limitation device that dynamically restricts the amount of power sent to the grid, ensuring the network is never overloaded. In practice, this allows larger systems to connect in constrained areas, with the trade-off being that some generation may be curtailed during periods of high solar output and low on-site consumption.

The distinction between G98, G99, and G100 causes confusion even among experienced property managers. G98 is the simplified connection process for small-scale systems up to 3.68 kW per phase — relevant for domestic installations but almost never for commercial projects. G99 is the main application route for larger systems and comes in two forms: Type A for systems up to 50 kW connected at low voltage, and Type B for larger or more complex connections. G100 is the export limitation framework. A single project may involve both a G99 application and G100-compliant equipment if the DNO imposes export restrictions.

The documentation required for a G99 application is comprehensive. Your installer must provide a completed G99 application form, a single-line diagram showing the electrical layout, inverter specifications and G99 type-test certificates, protection settings, and an earthing arrangement diagram. Missing or incorrect documentation is the most common cause of delays. Reputable commercial installers will handle this entire process on your behalf, but it is worth understanding what is involved so you can track progress and ask the right questions.

One frequently misunderstood aspect is the cost. A standard G99 application fee is typically between £250 and £500, but this only covers the DNO's administrative assessment. If the DNO identifies the need for network reinforcement — such as upgrading a substation transformer or reconductoring overhead lines — the costs can escalate significantly. In extreme cases, reinforcement costs can reach tens of thousands of pounds and fundamentally change project economics. This is why a thorough feasibility assessment that includes a pre-application enquiry to the DNO is worth its weight in gold.

The introduction of smart inverters with G100-compliant export limitation has been transformative for commercial solar in constrained network areas. Modern inverters can monitor grid export in real time and throttle generation within milliseconds to stay within agreed limits. When paired with battery storage, any generation that would otherwise be curtailed can be diverted to charge batteries instead of being lost entirely, significantly improving the economics of export-limited systems. This solar-plus-storage configuration is increasingly the standard approach for larger commercial installations in urban and industrial areas.

At Bee Solar, we manage G99 and G100 applications as a core part of every commercial installation project. Our in-house electrical engineering team prepares and submits all documentation, liaises directly with DNO engineers, and tracks applications through to approval. We submit the G99 application immediately upon contract signature, which is typically the longest-lead item in the entire project timeline. For clients exploring solar for the first time, we also offer a standalone pre-application enquiry service that provides indicative grid capacity and connection costs before any financial commitment is made. Early knowledge of your grid connection position is the most valuable information you can have when building the business case for solar.