Why the connection offer is not the whole cost
A Section 16A connection offer, as issued by a DNO under the Electricity Act 1989, covers the costs the DNO will charge for connecting your generation to its distribution system (Electricity Act 1989, s.16A). It does not cover the costs your electrician, engineer, or installer will incur on your side of the meter. It also does not always reflect the full scope of electrical infrastructure your site will need.
The distinction matters because developers sometimes build financial models against the connection offer alone, only to discover at the detailed design stage that protection equipment, metering, civil works, and commissioning add a material sum on top. For a 100kW solar project, those additional costs are rarely trivial.
What is inside a DNO connection offer
A formally issued connection offer under Section 16A of the Electricity Act 1989 must specify the charges payable under Section 19 of the Act, which governs connection charges, together with any security deposit required under Section 20 (Electricity Act 1989, s.16A).
In practice, a connection offer for a 100kW generation installation will typically contain two main cost categories.
Extension asset costs are the costs of installing new network assets to extend the distribution system to your point of connection. This means the cables, switchgear, and any transformer tapping needed to bring the network to your site. These costs are charged to the developer in full: the Access SCR reforms did not change this. If the nearest suitable connection point is 300 metres away and requires a new underground cable run and a new pole-mounted switch, the extension asset cost can be substantial even on an unconstrained network.
Reinforcement costs (where applicable) cover upgrades to existing shared network assets required to accommodate your generation. Prior to April 2023, these were commonly charged to developers, sometimes running to six figures on constrained substations. The position has changed significantly since then, as set out in the next section.
The offer will also specify the connection offer expenses, the non-refundable fee the DNO charges for preparing the offer (Electricity (Connection Offer Expenses) Regulations 2018). For a 100kW distribution-level connection, this is typically in the range of £500 to £2,500 depending on the DNO and the complexity of the assessment.
The Access SCR shift: who pays for reinforcement now?
Ofgem's Access and Forward-Looking Charges Significant Code Review (Access SCR), concluded in May 2022 and implemented from 1 April 2023, changed the rules on reinforcement cost allocation in a way that benefits developers connecting renewable generation (Ofgem, 2022).
Under the reformed regime, DNOs are expected to fund network reinforcement proactively, treating it as shared network investment and recovering costs through distribution use of system (DUoS) charges — the standing charges all network users pay. The developer still contributes to reinforcement at their own connection voltage level (and one voltage level above), but only up to the High-Cost Project Threshold; reinforcement beyond that, and at higher voltage levels, is funded by the DNO and recovered through DUoS charges.
The High-Cost Project Threshold (HCPT), set out in the Electricity (Connection Charges) Regulations guidance, provides the key boundary. For generation connections, the threshold is £200 per kW of generation capacity (Energy Networks Association, 2024). For a 100kW project, this means the first £20,000 of reinforcement costs is assessed against the threshold; costs above £200/kW are treated as the DNO's responsibility rather than the developer's.
Two important caveats apply. First, the HCPT applies to reinforcement of existing shared network assets, not to extension assets: the new cables and switchgear running to your site are still your cost. Second, the transition to proactive reinforcement funding has been uneven across DNOs, and some areas continue to carry legacy capacity constraints that produce complex offers. If the substation your site would connect to has been in a queue for reinforcement for years, the practical effect of the reform may not yet be visible in the offer you receive.
[FIGURE: Suggested diagram showing two cost categories in a typical 100kW connection offer: extension assets (developer pays in full) vs. reinforcement (HCPT applies, developer may pay nothing or partial). To be produced separately.]
Costs that do not appear in the DNO offer
Several categories of project cost sit entirely outside the connection offer and are often underestimated in early project budgets.
Protection relay and interface equipment. G99 compliance requires approved protection relays, interface systems, and typically a loss of mains protection device. The equipment itself, together with installation and configuration, typically costs £3,000 to £8,000 for a 100kW installation. These costs are borne by the developer, not the DNO, and must be procured separately.
CT metering. A 100kW solar installation operating under G99 requires current transformer (CT) metering to measure export accurately. Installation costs are typically in the region of £1,500 to £3,500, though this varies by site complexity and DNO requirements.
Electrical design and engineering fees. Preparing the G99 application, producing the single-line diagram, and specifying the protection scheme requires qualified electrical engineering input. Consultant or design-and-build contractor fees for this work typically run to £2,000 to £8,000 depending on system complexity. These fees are incurred before the formal connection offer is even issued.
Civils and trenching. Where the connection requires below-ground cabling on the developer's land (from the inverter to the metering point, for example, or from the boundary of the site to the point of connection), civils costs including trenching, ducting, and reinstatement can add several thousand pounds. On a constrained rural site, where the connection point may be some distance from the generation asset, this can be a significant item.
Commissioning and witnessed tests. For G99 installations, the DNO may require a witnessed protection test before the connection is energised, meaning a DNO engineer must attend site to verify the protection scheme operates correctly. DNO attendance fees vary but can run to £1,000 to £3,000, and the developer's contractor must also be present. Some DNOs carry out Type B and above witnessed tests for generation above certain thresholds. Type B covers generation above 1MW up to 10MW; Type C covers 10MW to 50MW; Type D covers 50MW and above or over 110kV. All three types require witnessed tests for all systems (Ofgem, 2026).
Delay costs. In heavily constrained areas, where the formal offer cannot be issued within the standard 45 working days or where reinforcement works are required before the connection can be made, project financing costs continue to accumulate. The cost of carrying a project in development for an additional six to twelve months — in consultant time, land option fees, and financing — is not captured in any DNO document but can be one of the largest items of all.
A worked cost breakdown for a 100kW solar installation
The table below sets out indicative cost ranges for a 100kW solar grid connection under three scenarios: an unconstrained site with available substation capacity, a moderately constrained site requiring some extension asset work, and a heavily constrained site where extension assets are significant.
| Cost item | Unconstrained site | Moderately constrained | Heavily constrained |
|---|---|---|---|
| Connection offer expenses (non-refundable application fee) | £500–£1,000 | £1,000–£2,000 | £1,500–£2,500 |
| Extension assets (cables, switchgear to connection point) | £3,000–£8,000 | £15,000–£40,000 | £50,000–£100,000+ |
| Reinforcement (post-HCPT, developer share) | Nil | Nil–£5,000 | Nil–£20,000 |
| Security deposit (refundable) | £2,000–£5,000 | £5,000–£15,000 | £10,000–£25,000 |
| Protection relay and interface equipment | £3,000–£6,000 | £3,000–£8,000 | £4,000–£8,000 |
| CT metering | £1,500–£2,500 | £1,500–£3,000 | £2,000–£3,500 |
| Engineering and design fees | £2,000–£5,000 | £3,000–£8,000 | £4,000–£10,000 |
| Civils and trenching | £1,000–£3,000 | £3,000–£10,000 | £5,000–£20,000 |
| Commissioning and DNO attendance | £1,000–£2,000 | £1,500–£3,000 | £2,000–£4,000 |
| Total (approx., excl. deposit) | £12,000–£27,500 | £28,000–£74,000 | £68,500–£168,000+ |
Ranges are indicative and based on publicly available cost data from DNOs and industry sources. Actual costs depend on the specific DNO, site geography, voltage level, and the scope of extension works required.
The security deposit is returned once the connection is made and the developer has demonstrated commitment, so it is not a net cost, though it represents a significant working capital requirement during the development period.
How location and constraint change the numbers
The largest single variable in the cost of a 100kW solar connection is geography: specifically, where the nearest available connection point sits on the distribution network and how constrained the relevant substation is.
In areas where the 11kV distribution network has headroom — typically parts of the Midlands and Wales served by National Grid Electricity Distribution, or recently reinforced substations across other DNO regions — a 100kW solar installation may connect with minimal extension asset costs. The offer may involve a short cable run, standard switchgear, and no reinforcement contribution at all. Total developer-side connection costs in these scenarios are typically in the £15,000 to £30,000 range.
In heavily constrained areas, particularly parts of Scotland (SSEN and SP Energy Networks areas), the South West and East Anglia (National Grid Electricity Distribution and UK Power Networks), and rural areas of Yorkshire and the North West (Northern Powergrid and Electricity North West) where distributed solar generation has grown fastest relative to network capacity, the picture is very different. Extension assets alone can exceed the capital cost of the solar array itself. Even with the Access SCR reforms limiting reinforcement charges, the cost of extending the network to a site that is far from a suitable connection point has not diminished.
Ofgem's connections reform programme, operating through the National Energy System Operator (NESO), is beginning to address some of these constraints through strategic network investment ahead of need (Ofgem, 2026). However, the relief is not evenly distributed, and many sites in constrained areas will continue to face extension asset costs that make the economics difficult.
How Feasibly can help
The difference between a £20,000 connection and a £100,000 connection for the same size solar array often comes down to which substation the site is closest to, and whether that substation has capacity. That information is available before a developer commits to a site, a planning application, or an option payment — but only if it is actively sought out.
Feasibly queries live DNO heat maps and capacity datasets, making it possible to assess the connection landscape for a given location before incurring G99 application fees. For a 100kW project, knowing whether the nearest suitable connection point is 50 metres or 500 metres away, and whether the relevant substation is amber or red on the DNO heat map, can determine whether the project is viable before any material cost has been committed.
Conclusion
The headline figure on a grid connection offer tells only part of the story. For a 100kW solar installation, total connection-related costs depend on three things: the cost of extending the network to the site, the residual reinforcement costs after the Access SCR threshold, and a set of developer-side costs — protection, metering, engineering, civils, and commissioning — that the offer does not cover.
The 2023 Access SCR reforms genuinely improved the position for developers on reinforcement: the high-cost project threshold means that expensive network upgrades are increasingly a cost for the DNO and network users collectively rather than for the individual project. But extension assets remain a full developer cost, and in constrained areas they remain the biggest single variable in a project's financial model. Understanding the full cost picture before the application is submitted is not just prudent, it is the only basis on which project viability can be assessed with any confidence.