GUIDE · FOR UK SOLAR INSTALLERS · 11 MIN READ

Grid Connections Reform: What Solar Installers Need to Know

Ofgem approved the reform (TMO4+)

15 Apr 2025

Ofgem approved the reform (TMO4+)

Transmission threshold in England and Wales, on export capacity

5MW

Transmission threshold in England and Wales, on export capacity

Threshold in mainland Scotland (50kW on the islands)

200kW

Threshold in mainland Scotland (50kW on the islands)

Last Gate 2 distribution offers due, on NESO's Feb 2026 timeline

Mar 2027

Last Gate 2 distribution offers due, on NESO's Feb 2026 timeline

Ofgem has said new connection offer dates were stretching into the 2040s, and customers who read that ask whether their roof is stuck in the same queue. Below the threshold, it isn't. This guide explains what Ofgem and NESO changed, which jobs it touches, where the offers have got to, and what it means for a G99 application. The forms themselves are in our G99 application guide and DNO application guide.

Last updated 21 October 2026. The reform is still being rolled out and its dates have moved before, so check NESO's timeline and your DNO for the current position. General information from Ofgem, NESO and DNO sources, not advice on a particular connection.

What changed

Ofgem's case for reform was a queue far bigger than the system needs. It reported 444GW of new connection applications across transmission and distribution in 2023/24, against 233GW in 2019/20, and said the queue held far more generation than needed for Clean Power 2030 and net zero by 2050.

On 15 April 2025 Ofgem approved NESO's reform package, known as TMO4+. Its aim, in Ofgem's words, is connection on a "first ready first connected" basis. Projects in scope now need to be:

• Ready — for most projects, obtaining, evidencing and keeping exclusive land rights, and progressing planning within a set period.
• Needed — for most, aligned with the capacities in the government's Clean Power 2030 Action Plan. Demand-only projects are automatically treated as needed.

Projects that meet both get a Gate 2 offer, with a confirmed connection date, connection point and queue position. Projects that don't get a Gate 1 offer, which is indicative, and can reapply in a later window once they're ready. The same tests were applied to the existing queue, in a process called "Gate 2 to Whole Queue". Some projects were protected, including those due to connect in 2026.

Who it applies to

The reform is led from transmission. It covers projects connecting to the transmission network, and generation and storage projects connecting to the distribution network that qualify for a Transmission Impact Assessment (TIA), NESO's check of a distribution project's effect on the transmission network. Ofgem says smaller generation and storage projects, and all demand projects connecting at distribution, are out of scope.

So the threshold decides it:

The England and Wales change came from Ofgem's CMP446 decision of 12 May 2025. Before it, a TIA was needed above 1MW. Ofgem approved the version that measures the threshold on export capacity, the most power that can be transferred to the distribution network, after any on-site use, rather than the generator's full capacity. NESO estimated the change affected 337 projects in the queue, 682MW in total. Where a grid supply point has little or no fault level headroom, the threshold stays where it was. Ofgem said Scotland's lower thresholds, which have their own technical reasons, were being reviewed separately.

In practice: a rooftop job in England or Wales exporting under 5MW is below the threshold, so the reform's Gate 2 process isn't part of its connection. In Scotland, a rooftop system exporting more than 200kW on the mainland, or 50kW on the islands, can be.

Timeline and where offers have got to

• 15 Apr 2025Ofgem approves the TMO4+ connections reform package.
• 12 May 2025Ofgem approves CMP446: the Transmission Impact Assessment threshold in England and Wales rises from 1MW to 5MW, measured on export capacity.
• 26 Aug 2025The Gate 2 evidence window for the existing queue closes, extended from 29 July.
• Dec 2025NESO creates the new connections delivery pipeline.
• 8 Dec 2025Ofgem approves CMP448, the Progression Commitment Fee (in force 2 January 2026).
• 13 Feb 2026NESO and the network companies publish revised dates for issuing offers (below).
• Jun 2026Ofgem confirms the authority needed for the revised timeline.

The offer dates NESO and the network companies published on 13 February 2026 (clarified on 17 April 2026) are below. Offers are being released area by area as the technical work is finished, so some places get theirs earlier than others; NESO said Scotland would be first. NESO has removed the "no earlier than" date for the next application window, so there is no date for it.

"Protected" means projects contracted to connect by the end of 2026, and significantly progressed projects contracted to connect on or before 31 December 2027. At the time of writing, Phase 2 distribution offers are in their window.

What it means for G99 applications

Below the threshold: the reform's Gate 2 process doesn't apply. The job is applied for and connected through the DNO under G99 in the usual way. Our G99 guide covers the forms, the steps and the timescales, and the DNO application guide tells you which DNO to apply to.

Above the threshold: the project needs a Gate 2 offer for transmission access, applied for through the DNO. Ofgem's decision sets out how it works:

• If NESO confirms the project meets the readiness and needed criteria, it gives the DNO the connection date, costs, point of connection and technical details, and the DNO updates the offer. That is a Gate 2 offer.
• If it doesn't, NESO gives the DNO an indicative date and point of connection, and the DNO makes the offer indicative. That is a Distribution Gate 1 offer. Such projects don't keep a queue position or capacity at distribution.
• A project also goes to Distribution Gate 1 if it rejects a Gate 2 offer, doesn't apply or submit evidence, or withdraws. It can apply again for Gate 2 later, through the DNO, if it meets the criteria then.

For an installer, the point is timing: on an in-scope job the firm connection date comes from NESO's Gate 2 process, not from the DNO alone, so don't commit to a date in the contract that the offer hasn't given you.

Connection costs

What a distribution connection costs is set by the DNO's charging methodology, which Ofgem changed from 1 April 2023. Since then a generation connection pays for the new extension assets and a contribution to reinforcement at the voltage level of the point of connection (a "shallow-ish" boundary). A demand connection pays for extension assets only. Whether the DNO charges to assess a G99 application is covered in the G99 guide.

For in-scope projects there is one new cost to know about. On 8 December 2025 Ofgem approved CMP448, a Progression Commitment Fee for projects in the Gate 2 queue, in force from 2 January 2026. Its purpose is to encourage unviable projects to leave the queue in good time, and Ofgem says it will be activated only when the need arises. It applies to the Gate 2 queue, which projects below the threshold aren't in.

Network capacity maps

Before you promise a customer a big export, look at what the local network can take. DNOs publish their own data:

• National Grid Electricity Distribution's Network Opportunity Map gives an indication of demand and generation headroom at Bulk Supply Point and Primary substations, colour-graded towards where a connection is more likely without significant reinforcement.
• DNOs publish an Embedded Capacity Register. SSEN's register lists generation and storage of 50kW and above that is connected or accepted to connect, and is updated monthly.

These are indicative. They help you spot a constrained area early; the DNO's offer is the answer. To find which DNO covers the site, use the MPAN lookup in our DNO application guide.

When export limitation is the practical route

Where the local network is tight, or the full export would need reinforcement, limiting the export with a scheme that meets EREC G100 can be the way to a workable offer. Our G100 export limitation guide explains how schemes work, the fail-safe rules and the forms.

It also matters for the reform. Because the England and Wales threshold is measured on export capacity, it is the export in the connection, not the size of the array, that is compared with 5MW. Agree the export figure with the DNO in the application, and check how they'll treat it before you rely on it.

Installer checklist

1. 1Size the export, not just the array. In England and Wales the transmission threshold is measured on export capacity. Know the export the job needs before you apply.
2. 2Check which side of the threshold it is. Below the Transmission Impact Assessment threshold, the reform's Gate 2 process doesn't apply and the job goes through the DNO's normal G99 process. Above it, it does.
3. 3Know the Scottish numbers. In mainland Scotland the threshold is 200kW, and 50kW on the islands, so a large rooftop job there can be in scope.
4. 4Look at network capacity before you quote. DNO capacity maps and the Embedded Capacity Register show where generation headroom is tight. They are indicative, but they tell you which sites to ask about early.
5. 5Consider export limitation. Where the network is constrained, a G100 export limitation scheme can keep the export within what the network can take. Agree it with the DNO in the application.
6. 6Tell the customer what the timeline depends on. If a job needs transmission access, its firm date depends on Gate 2. Don't promise a connection date the DNO hasn't given you.

The supply and export questions belong in the first site visit. See the commercial solar survey checklist.

Grid connections reform: FAQ