G99 and grid connection
Grid connection is one of the most common sources of surprise cost and delay on a commercial solar project — and one of the easiest things for a proposal to leave vague.
What G99 is
G99 is the industry engineering recommendation that governs connecting generation equipment — including commercial solar — to the UK distribution network above the small-scale threshold covered by the simpler G98 process. In practice, most commercial systems need a G99 application to your local Distribution Network Operator (DNO) before the system can be connected and exported to the grid.
Why it can add cost and time
- Application and assessment time. DNOs assess whether the local network can accept your system as proposed; this can take weeks to months depending on the DNO and local network capacity.
- Network reinforcement. If the local network can't accept your full proposed capacity without upgrades, the DNO may require (and charge for) reinforcement work — this can be a significant, project-specific cost that isn't always visible until the application is assessed.
- Export limitation. An alternative to reinforcement is agreeing to limit how much you export, which can affect the economics of a larger system.
What to check in a proposal
- Is the G99 application fee included in the price, or billed separately?
- Who bears the cost if the DNO requires network reinforcement?
- Is an export limitation assumed, and if so, has it been factored into the generation and savings figures?
- What happens to the project timeline if the DNO assessment takes longer than expected?
These questions are part of the scope comparison in our proposal review — see the full quote checklist for everything else worth checking.