DNO Heat Maps: How to Check Grid Capacity for Commercial Solar

Updated 23 October 2026 · SEO Dons Editorial

What does a DNO heat map show?

A distribution network operator (DNO) heat map colours the operator's substations by how much more generation or demand they can take. NGED says the colour gradings of its map "are intended to guide the user to areas of the network where a connection is more likely to be achieved without significant distribution reinforcement". It screens a site before a connection application and does not replace one.

Most maps work at primary substation, bulk supply point (BSP) and grid supply point (GSP) level. Northern Powergrid (NPg) describes its heat maps as an overview "at Primary, Bulk Supply and Grid Supply Point level using a traffic light system". The colour reflects more than spare megawatts: NPg calculates thermal headroom from firm capacity, demands and existing and contracted generation, then checks fault level, tapchanger and other constraints.

Who publishes which map, and where is it?

The Energy Networks Association (ENA) lists "all the online resources and tools" that operators provide for connection customers. This table picks out the generation-relevant ones for the six GB groups.

Operator	Licence areas	Where to look
National Grid Electricity Distribution (NGED)	East Midlands, West Midlands, South West, South Wales	Network Opportunity and Development Map: demand and generation headroom at BSP and primary substations. Log in or register. Also its Embedded Capacity Register.
SP Energy Networks (SPEN)	SP Distribution (Central and Southern Scotland); SP Manweb (Cheshire, Merseyside, North Shropshire, North Wales)	Green, amber and red heat maps, capacity heatmaps and the register on the SPEN Open Data Portal, which needs an account.
SP Electricity North West	North West England	Heatmap tool: Excel workbook and interactive map for all primary substations and BSPs. Embedded Capacity Register.
Northern Powergrid	North East, Yorkshire and northern Lincolnshire	Network heat maps (traffic light) and its register, in parts below and above 1 MW.
SSEN Distribution	Central southern England; northern Scotland	Generation Availability and Network Capacity map and heat map spreadsheets, and the register, on its data portal.
UK Power Networks (UKPN)	Eastern, London and South Eastern	LTDS Capacity Heatmap, Network Infrastructure and Usage Map and register on its open data portal. Registration needed.

Northern Ireland sits outside these six: NIE Networks publishes a network capacity map with demand, generation and fault level modes. In Wales, NGED serves the south and SP Manweb the north; the Wales page gives the national context.

What changed in 2026?

Ofgem's revised Form of Long Term Development Statement requires DNOs to publish Capacity Heatmap data. After an extension requested by the ENA for all six DNOs, Ofgem gives the publication date as 29 May 2026, and NPg, SPEN and UKPN now publish the result. UKPN calls it "a standardised view of available network capacity, constraints, and recent connection activity", and its version summarises budget estimates, offers made and offers accepted, which shows whether a substation's headroom is being taken up.

The earlier operator tools remain and formats differ, so read each map's own key. UKPN says of its heatmap: "To view this data please register and login."

How do you read the colours and numbers?

Definitions vary by operator. SPEN uses three categories. Green means "All operational factors are within tolerable limits" and a connection may be possible without reinforcement, subject to detailed studies. Amber means at least one factor is "nearing its operational limit" and reinforcement may be required. Red means installing most levels of distributed generation is "highly unlikely". NGED's capacity map page is gentler: connections at red substations "are still possible", but may need "significant network reinforcement".

Generation headroom. NGED calculates it from the reverse power capability of each site, counting connected, accepted and quoted generation.
Fault level. SSEN's spreadsheets include it, and SPEN notes that generation technology "contributes differently to system fault levels".
Upstream limits. SPEN says demand headroom depends on upstream network capacity and generation headroom on voltage constraints on export.
Contracted capacity. NIE Networks warns that capacity shown "may already be contracted to individual customers", and UKPN that unused capacity "may be contractually committed to customers".

What can a heat map not tell you?

It cannot give terms for a particular site. Electricity North West says its tool "cannot replicate the level of accuracy provided by the detailed assessment" in the formal application. NIE says its map "cannot be relied upon to assess the terms of connection for specific premises", and SPEN says its capacity heatmaps do not replace the formal connections process.

Most maps also stop at primary level. NIE states that its map "gives constraints down to primary substation level only" and that 33 kV availability "does not infer availability on the lower voltage levels". An array of 50 or 100 kW may connect below that level, so the local feeder and transformer matter, and some operators publish them: Electricity North West has a dataset on transformer capacity at each distribution substation on its high voltage network. Dates differ too. Electricity North West's heatmap workbook is dated 22 October 2026, while NIE's map data was last updated on 26 June 2026.

What does the Embedded Capacity Register add?

The Embedded Capacity Register (ECR) lists generation and storage of 50 kW or more that is connected or accepted to connect. Electricity North West says the register uses "an industry agreed format" that has been "adopted by all Distribution Network Operators". NGED, Electricity North West and SSEN update it monthly, NPg by the 10th working day of each month. It is not complete: UKPN notes that completeness "may be impacted by low asset registration by DER installers". Systems below 50 kW are outside its threshold; the 50 kW page and 100 kW page show where that line sits.

How do you screen a site with the maps?

Identify the operator and licence area; ENA's network operator finder does this by postcode.
Open that operator's map and search the postcode. Note the nearest primary substation or BSP, its status, any constraint named and the date of the data.
Check the ECR for accepted generation nearby.
Compare the inverter's kW, not the panels' kWp, with the map. NGED's G99 page says solar PV is sized from the inverter's continuous steady state output.
Size the array to the building's demand, decide whether to plan an export limit, and take the findings into the quote conversation. The commercial PV systems guide shows where the grid step sits.

What can you do when the map shows red?

Red is not a refusal. Options include:

Export limitation. SSEN says an export limitation scheme "may be significantly cheaper than paying to reinforce" the network and "may also mean that you can connect your generation more quickly". The export limitation guide explains how G100 schemes work.
Managed connections. SPEN publishes data on "daily aggregated generation losses caused by curtailment" under its active network management and load management schemes, which shows what such a connection can cost in lost output.
Alternative offers. NGED's "Study & Offer" approach lets a customer ask it to consider "up to 3 different capacities", with alternative connections where the network is constrained.
A smaller or staged array, sized to on-site demand, or storage to absorb the midday surplus.

The industry's Gate 2 to Whole Queue reform tracks connections "at 1MVA/1MW and above", so arrays under 1 MW sit outside it (the grid connection reform guide covers the programme). A contractor can check a site against these maps, and you can send an enquiry through the site's form.

Sources

Energy Networks Association, connections data and network operator finder, checked 22 October 2026.
Ofgem, Long Term Development Statement direction, checked 22 October 2026.
National Grid Electricity Distribution, Network Opportunity and Development Map, network capacity map, register and G99 page, checked 22 October 2026.
SP Energy Networks, Open Data Portal dataset descriptions, checked 22 October 2026.
SP Electricity North West, heatmap tool, register and open data dataset descriptions, checked 22 October 2026.
Northern Powergrid, heat maps, register and dataset descriptions, checked 22 October 2026.
SSEN Distribution, capacity map dataset, register and microgeneration page, checked 22 October 2026.
UK Power Networks, capacity heatmap, usage map and register, checked 22 October 2026.
NIE Networks, network capacity map, checked 22 October 2026.

Common questions

Do I need an account to open a DNO capacity map?

Often. NGED asks users to log in or register before opening its Network Opportunity and Development Map, UKPN says its capacity heatmap needs registration and login, and the ENA notes that SPEN's portal requires an account. Electricity North West offers its heatmap workbook as a download.

Does a green substation mean my array can connect?

No. SPEN says green means opportunities "may exist" to connect without reinforcing the network, "subject to detailed studies". Local feeders, the transformer serving the site and other applications ahead of yours do not appear on a primary-level map, so a formal assessment is still needed.

Will a 40 kW array appear in the embedded capacity register?

Normally not. The register covers generation and storage of 50 kW or more that is connected or accepted to connect, so a smaller system falls below its threshold. A system at or above 50 kW would be expected to appear once it is connected or accepted.

How often do capacity maps and registers update?

It varies. The register is updated monthly at NGED, Electricity North West and SSEN, and by the 10th working day of each month at NPg. Heatmap dates differ too, so check the date on the map you use.