G99 vs G100: When Export Limitation Saves Your Solar Project

The grid is full. So what?

A third of the commercial G99 applications we submit in 2026 come back from the DNO with a "no capacity, reinforcement quote attached" letter. The reinforcement quotes range from £15,000 to £450,000. The reinforcement timelines range from 6 weeks to 24 months. For most businesses, neither the cost nor the timeline is acceptable.

G100 export limitation is the alternative: design the system to limit exports below the available grid threshold (often 0kW), and the DNO will approve the install without reinforcement, in a routine G99 timeline.

The trade-off

Export limitation costs you the SEG revenue you would have earned on exported kWh. For a typical UK commercial site with 70%+ self-consumption, that loss is around 4–6% of total system output — economically immaterial against the cost and time saved.

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.

The decision belongs in the spreadsheet, not the brochure. We model both cases for every site.