Why We Recommend G100 Export Limitation 80% of the Time

The grid reality in 2026

A third of the G99 applications we submit in 2026 come back from the DNO with a reinforcement quote attached — typically £15,000 to £450,000, with timelines of 6 weeks to 24 months. For most commercial businesses, both the cost and the timeline are deal-breakers. G100 export limitation is the practical alternative: design the system to limit exports below the available grid threshold (often 0kW), and the DNO will approve the install without reinforcement, on a routine G99 timeline.

What G100 actually does

A G100 device is a small monitoring CT clamp at the building's main incomer, connected to the inverter. The CT measures the net flow at the incomer in real time. When the building's load is below the solar generation, net flow is outward (export); the G100 device commands the inverter to throttle output until the net export is at or below the set threshold. When the building's load rises, the throttle relaxes and the solar inverter produces its full available output.

The cost — actual generation lost

On commercial sites with high daytime self-consumption (factories, warehouses, supermarkets, hospitality), G100 export limitation activates only when net export would exceed the threshold. For a typical KMM commercial install with 75%+ self-consumption, that means G100 cuts in for:

• 22-35 minutes per typical weekday (lunch hour when load dips and sun is high)
• 3-6 hours per Sunday (closed days when load drops)
• Total: roughly 3-6% of total annual generation lost to export limitation

What G100 saves

The reinforcement contribution avoided typically runs £50,000 to £300,000 on a 500kWp-1MWp project. The project starts 6-12 months earlier than it otherwise could. Both translate directly to faster payback and earlier savings realisation.

When G100 doesn't work

For sites with low daytime self-consumption — weekday-empty schools and offices in summer, retail with significant Sunday closure, agricultural sites with seasonal load — G100 export limitation can curtail 15-25% of output. At that level, the maths starts pointing toward either a battery to absorb the export, or paying the reinforcement contribution to unlock the grid. We model both cases for every project.

The 80% number

Looking back at our 2025 and 2026 commercial project pipeline, around 80% of projects above 250kVA either chose G100 or had it offered as the cheapest alternative to reinforcement. That share rises to over 90% in UK Power Networks territory (London, SE England) where reinforcement queues are particularly long.