Electricity grid capacity and when it stops a scheme

A distribution network operator cannot usually stop a planning permission, but it can stop a building being occupied. That is the real shape of the grid capacity planning application problem. Councils rarely refuse schemes for lack of electrical capacity, because capacity is a deliverability matter rather than a policy objection. What capacity does instead is break the link between permission and delivery, and it does so most sharply on all-electric schemes where heat pumps and vehicle charging have replaced a gas connection.

So the evidence a planning application needs is not an argument about the grid. It is a dated position from the network operator and a phasing plan that works with it.

Why capacity became a planning issue

Three changes arrived together. Heat pumps moved the heating load onto the electrical supply. Vehicle charging added a second large load to each dwelling and to commercial parking. And the removal of gas from new development, through building regulations tightening and local policy, took away the alternative.

The result is that the assumed electrical demand per dwelling used in network design has risen, and the margin that used to absorb a new connection has gone in many areas. Operators publish their own demand assumptions and their own capacity heat maps, and those assumptions are what the connection offer will be calculated on, so read them before estimating the load.

For planning, this surfaces in three ways: a consultee comment from the network operator or the authority's climate team, an objection that the energy strategy is undeliverable, and a condition or obligation about phasing.

Getting a capacity position you can rely on

There are several products, and they are not interchangeable.

A heat map is not evidence of anything specific to your site. A budget estimate names a likely point of connection and gives a cost order, which is usually enough for a planning submission. Only a formal offer tells you the date.

What to supply with the enquiry: the site address and boundary, the number and type of units, the proposed heating system and its design load, electric vehicle charging provision and its diversified load, any commercial loads, on-site generation and storage capacity, and the intended phasing with dates. An enquiry submitted without a load estimate comes back with a generic answer.

Where the connection is large enough to affect the transmission system, the operator has to refer the application upstream before it can offer firm terms, which adds months. Ask whether that applies as part of the enquiry rather than discovering it later.

Reading a connection offer

Four items in an offer matter for planning.

The point of connection, which determines whether cables cross third-party land. Wayleaves and easements over land you do not control are a programme risk and sometimes a Grampian condition.

The capacity offered, in kVA, against the capacity requested. Partial offers are common and the shortfall is what the phasing plan has to accommodate.

The charges, split between sole-use assets and any contribution to wider works. Charging arrangements for demand connections were reformed so that customers are generally no longer asked to fund wider network reinforcement beyond the point of connection, with those costs recovered through use-of-system charges instead. The arrangements continue to change, so check the current charging basis rather than relying on an older project's experience.

The programme, and the offer's validity period, which is short. An offer accepted late loses its place.

Reinforcement, who pays, and what to tell the council

Where reinforcement is needed, the questions for the application are not about cost allocation. They are about time and certainty.

A substation upgrade within the operator's own programme is a different proposition from one triggered by your connection alone, and the operator's investment programme is published. Where the works are already funded and programmed, say so and give the date. Where they are not, the honest position is that the connection date is uncertain, and the application should deal with that through phasing rather than through optimism.

If a new substation has to sit on the site, it needs to be on the planning drawings with its footprint, access for a transformer delivery, ventilation and acoustic treatment. A substation added after permission is a non-material amendment application at best and a redesign at worst.

Phasing a scheme around a connection date

This is the practical answer, and councils accept it when it is set out properly.

1. Establish the connection date for the capacity available now, and for the full capacity.
2. Split the scheme into phases whose cumulative load sits inside each capacity step.
3. Show the phasing on a plan, with unit numbers and loads per phase.
4. Propose a condition tying occupation of later phases to the provision of the connection capacity, drafted so the trigger is a measurable event.
5. Where the works are on land outside your control, check that a condition requiring them is appropriate at all. A condition dependent on third-party action is only reasonable where there are realistic prospects of it being carried out, which is the established test.

A temporary arrangement sometimes bridges the gap: a smaller connection with active load management, a battery to shave peaks, or a temporary generator for construction power. All three are legitimate and all three need describing rather than implying.

Load management as mitigation, honestly

Demand-side measures reduce the connection size needed, and they work. Diversity in vehicle charging through smart charging, time-of-use scheduling for hot water, thermal storage on heat pump systems and battery storage sized to the peak all reduce the kVA requested in practice.

The limitation worth stating plainly. Load management reduces peak demand, not the energy delivered, and it depends on control systems being installed, commissioned and left operational by occupiers. A network operator will accept a diversified load figure based on recognised assumptions. It will not accept a figure that depends on residents behaving in a particular way without any technical constraint.

Fabric comes first in any case, because a lower heat demand means a smaller heat pump and a smaller connection. Glazing ratio is a significant part of that, as heat loss from glazing ratio and design policy sets out, and on-site generation changes the net position, which is where roof area arithmetic comes in.

Evidence to put in the application

Put the capacity position in the Energy Statement rather than in a separate note, and make it specific.

The load calculation, with the assumptions named: heating design load, hot water, vehicle charging provision and the diversity factor applied, commercial loads, and the resulting maximum demand in kVA.

The enquiry correspondence, dated, with the operator's reference and its response in full rather than summarised.

The phasing plan, with loads per phase.

The metering and submetering arrangement, which matters for mixed use schemes and affects both the connection design and the eventual billing, as metering and submetering strategies for mixed use explains.

Any substation or switchroom shown on the drawings, with dimensions and access.

And a short statement of what happens if the connection is later than expected. Officers respond well to that because it is the question they are actually worried about, and grid connection capacity as a planning constraint covers how it is weighed in the balance.

PlanScope can draft an Energy Statement that carries the load assumptions and the connection evidence in a structure officers recognise, flagging the figures that need confirming from the operator. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Electrical load design is engineering work for a qualified designer. This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.