UKPN Grid Connections for London Solar
Every commercial solar system in London connects to UK Power Networks' distribution network, and the G99 application is the one piece of paperwork that can move your whole programme. Here is how it works and how to keep it off the critical path.
Who UKPN are and why they decide your timeline
UK Power Networks operates the distribution network across London, the South East and the East of England — the cables, substations and transformers between the national grid and your meter. Connecting generation to that network requires their permission under the G99 engineering recommendation for anything above 16A per phase, which in practice means every commercial system. The installation itself takes weeks; UKPN's assessment takes anywhere from one to three months. Projects that treat the application as an afterthought discover this the expensive way.
What UKPN assesses
The question is always the same: can the local network absorb your export without voltage or thermal problems? London's urban network is, on the whole, strong — dense, well-reinforced, built for heavy loads. Three answers come back. Clean approval: common for systems sized to building load in well-served areas. Approval with export limitation: increasingly standard for larger systems on busier feeders — you connect now, with a cap on export enforced by a control device. Reinforcement quotation: the rare-in-London case where full export requires network upgrades, priced to the applicant. For most London businesses the second outcome is commercially trivial, because city buildings consume the bulk of what they generate anyway.
The London sequencing play
Our standard sequence puts the G99 application immediately after desk feasibility, in parallel with the planning check and survey — not after the contract is signed. The application requires a stable single-line diagram and inverter schedule, both available once the preliminary design exists. Done this way, UKPN's response arrives while procurement and logistics planning proceed, and the installation slots in as approval lands. Done the other way, a signed contract waits two months for permission to connect — same project, slower cash flow.
Costs to expect
Application and witnessing fees for typical commercial systems run from a few hundred pounds to around £2,500, and belong inside any complete quote — check before comparing bids. Export limitation hardware, where required, adds £1,500–£4,000 depending on system architecture. Reinforcement, in the unusual London cases where it is the chosen route, is priced by UKPN's formal quotation and evaluated against the export-limited alternative; at city self-consumption rates, limitation usually wins. All of these lines appear itemised on the London costs page.
Commissioning and witnessing
Larger systems are witnessed at commissioning: UKPN attends (in person or by agreed evidence) while protection settings are proven — the relays that disconnect the system if the network fails — and any export limitation scheme is demonstrated working. Witnessing is routine when the design matched the application; it bites only when installers deviate mid-project, which is one more argument for the boring discipline of building what was applied for. After witnessing, the system is energised, registered and generating — and the only remaining UKPN interaction is the export meter doing its quiet work.
UKPN connection questions
What is the difference between G98 and G99?
G98 is the simplified notify-and-connect route for very small systems — up to 16A per phase, about 3.7kW single-phase or 11kW three-phase. Practically no commercial system qualifies. G99 is the application route for everything larger: UKPN assesses the network impact before granting permission to connect. Commercial solar in London means G99, applied for before installation, every time.
How long does UKPN take to approve a commercial solar connection?
Smaller G99 applications (under ~50kW on healthy network) often clear in 4–8 weeks. Larger systems needing a network study run 8–12 weeks, occasionally longer where reinforcement options are being priced. This is why the application goes in as soon as the design stabilises — UKPN's clock, not the installation, sets most London project timelines.
What does export limitation mean for my returns?
An export limitation scheme caps what your system can push onto UKPN's network, enforced by a fast-acting control device. Your on-site consumption is untouched — and since on-site use is worth 25–30p/kWh against 4–12p for export, a cap typically costs a London business a few hundred pounds a year at most. It is almost always the right answer when the alternative is paying for reinforcement.
Do we need a new supply or substation for solar?
Rarely for rooftop-scale projects. Systems up to a few hundred kW normally integrate on the LV side of your existing supply. Sites with their own HV substation integrate behind it. The cases that get complicated — very large arrays on modest supplies — are exactly what the G99 study exists to resolve, and why no fixed price should precede UKPN's answer on a big system.