Obtaining import and export permissions from your Distribution Network Operator (DNO)

  • 1 June 2021
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Obtaining import and export permissions from your Distribution Network Operator (DNO)
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The regional Distribution Network Operators (DNOs) must be contacted when permission is required for certain higher-power devices which import or export electricity. These include PV Solar Panels, Home Battery Storage, Wind Turbines, Electric Vehicle chargers and Heat pumps.


Export :

G98 (was G83); a single device which exports no more than 16A per phase (3.68kW) to the Distribution Grid.

G99 Fast Track; required for sites where two or more export devices are installed, but only one exports to the Grid. The other device(s) therefore have G100 accreditation (see below).

G99 Full; required for sites where more than one device can export to the Grid. Note that the assessment procedure is not the same as the G99 Fast Track calculations.

G100; a site or device generating more than 16A per phase, but which incorporates some form of export limitation. The limit must be declared even if it is Zero (ie all the energy is to be used within the site).


Import :  covers Low Carbon Technology (LCT)

Electric Vehicle charger. A domestic charger taking more than the power available from a 3-pin 13A socket outlet (3kW).

Since most domestic EV chargers are rated 7.5kW and will typically be used for a period of 2-8hours, there is an obvious drain on one-phase passing through the local sub-station transformer. Transformer imbalance causes energy-loss and is of concern to the DNO.

Heat pumps. Ground Source Heat Pumps (GSHP) or Air Source Heat Pumps (ASHP) taking more than 3kW peak.

The load imposed by a Heat pump is usually lower than an EV charger, and spread across the entire day. However, it is more likely to be operating during the early evening period of peak-demand. Heat pumps are known to cause voltage fluctuations (flicker) and create harmonics on the Grid. The DNO is required by Ofgem to minimise losses from such variations.

See Balancing the Grid tutorial.

See further down for more information on obtaining Import consent:



Export consent:


1: When can the G99 Fast Track process be used?

Assume a site which requires an Inverter delivering power from Solar Panels and a separate Storage Battery, both of which have a Grid connection.


Here is the Fast Track guidance from the Electricity Networks Association (ENA), which is the body representing British DNOs.


This complex set of criteria for G99 Fast Track applications is recreated in pictorial format below.


2:  G99 - Full application

G99 is most commonly used by community and commercial organisations who require a 3-phase connection to the Grid.

G99 also applies to single-phase domestic sites where

  • there is more than one device which can export
  • the level of export is to be greater than 3.68kW (16A)

The DNOs use a computer-modelling system which requires a number of parameters to be defined that are local to that site. The software outputs a number which is the percentage of voltage rise if the devices were to be approved.

The parameters required include:

  • the cable length between the site and the sub-station transformer
  • the cable characteristics; its cross-sectional area and composition
  • the number of houses between the site and the transformer
  • the transformer rating and its free capacity

The principle difference between the G99 and its Fast Track equivalent is the way in which the export potential of the on-site devices are calculated. This means it is possible for a site to be granted certification under G99 Fast Track, but to be refused if a Full Application were made.


3:  G100 - devices with export limitation

The G100 standard is most commonly referred to for the installation of PV Solar Panels on a house with an East/West facing roof.



The total output of both the East and West solar arrays can be higher than the permitted 3.68kW (16A) because the sun can’t fully fall on both sides of the roof simultaneously. Instead, the inverter is equipped with Export Limitation software. Such an inverter is certified to G100, which the DNO therefore accepts for grid-connection. The 3.68kW limitation cannot be exceeded, even when both arrays are in sunlight at midday.

The key point for G100 is that it contains accredited Export Limitation technology for whatever current is specified - usually 16A per phase.

Some Storage batteries have their limit set to zero.

When the export limit is zero, there cannot be any electricity sent to the Grid because this is locked into the design of the battery. All the energy stored can only be used within the house. A current-clamp attached to the Live supply cable provides the measurement which gives this assurance.

current measuring clamp on live feed to house


Import consent: 

A DNO cannot refuse you a connection to operate a high-current device. However, they can insist on an upgrade to your Service Fuse and/or its cable connection to the 3-phase supply in the road if that is inadequate to support the increased load.

Additionally, a DNO can request a financial contribution towards network infrastructure upgrades where your connection is deemed to impose a significant additional load. Typically this might be a charge of £1000 - £3000.


Guidance for the connection of Low Carbon Technology to the Distribution Network have been laid down by Electricity Networks Association. A single Flow-chart shows the required procedure for an EV charger, a Heat pump or both.



Either click on the above image to open it up, or download the chart as a PDF from the ENA’s Resources Library.


Applying to your DNO for Low Carbon Technology

The uptake of EVs and Heat pumps is happening faster than the application process can be streamlined.

Some DNOs, such as Western Power Distribution, have one web-page for EV Chargers, and a different one for Heat Pumps. Each application has a form which can be downloaded and then emailed to WPD, although this is only available in Microsoft’s DocX format at present.

In contrast, UK Power Networks in SE England have developed an online application system called Smart Connect. There are a few circumstances which make the online portal unsuitable, but it can cope with the majority of LCT Applications speedily. Here’s the link signposted from their advice page about Heat pumps


All Grid connections of EV chargers and Heat pumps must be notified, although this can sometimes occur after they are installed and commissioned (known as “Connect & Notify”). Check the Flow-chart above.

If you don’t know who your DNO is, then the ENA provides a web-page into which you can enter your Post Code.

They also retain a downloadable list of Network Operators’ contact details for EV applications. This includes information on the  ten Independent Operators, who are increasingly responsible for electricity distribution on new housing developments.

7 replies

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This is beautifully laid out and explained in a way that even I can understand.


Another top guide from our community’s first ever Plan Zero Legend @Transparent - helping people here in the UK to make informed decisions about the smart technologies that will power the country’s journey to zero carbon. 


I should point out that OVO haven’t fact checked this article. Also I’m curious to know, what propensity do DNOs have for rules changes? Can we be pretty confident the approach for both import and export devices will stay roughly the same?


I’m thinking for example, with the potential mass adoption of EVs, will the process and guidelines need to be adapted?


Great stuff, @Transparent thanks for sharing with us!

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Your curiosity is well founded @Tim_OVO 

I have already received an email from a DNO Network Development Engineer to say that new revisions are in progress for the G100 export certification and also the Fast Track Application process.

The ongoing changes to the rules are essential as the country moves rapidly towards distributed micro-generation, Smart Meters, electrification of heat, and widespread uptake of Electric Vehicles. For that reason this Tutorial will continually be updated with fresh information.

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How do I know if I can make a G99 Fast Track export application?

The Electricity Networks Association has introduced the Fast Track process in order to handle the growing demand for integrated micro-generation and storage.

The following simplified version of the ENA guidance assumes a site with

  • one generation device (a PV Solar array connected via an Inverter)
  • one Storage device (a grid-connected battery)

The ENA has published a downloadable guide to G98 available from their Resources Library. The process is simpler than G99 Fast Track and covers the majority of small domestic installations.

However, if your site has a total export capacity above 16A per phase, then you must proceed with G99. There are two further criteria required for the Fast Track process:


If the criteria above are not met, then the Fast-track scheme cannot be used. A full G99 Application must be made.

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My G99 charge/export levels on the V2G trial were initially set by WPD at 4kWh but when I objected and pointed out I had been charging at 7kW for three years and they had fitted a 100A fuse they increased the level to 5.5kWh.

I’m still waiting for an answer from WPD as to why I can’t operate at 7Kw; apparently the exporting is the problem but I can’t see why?


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Please clarify @PeterR1947 

1: are you telling us that the V2G charger is designed such that the import current and export current must be set to the same value?

2: Do you know if your charger was put through the G99 Full Application process rather than the Fast Track?

And if you want more specific detail, send me your post-code in a PM and I’ll check out your particular sub-station. WPD have allowed me access to their network mapping tool for just such a scenario. That map might give me a clue as to why they need to peg export at 5.5kW (24A).

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Hi @Transparent 


Re: 1. Yes

  1. Unsure, will send you my Postcode
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For the record may I just let others here know that I checked the local Distribution Grid where @PeterR1947 lives.

In order to allow any export greater than 3.68kW, his site application must’ve been for Full G99 approval.

That G99 assessment does this:

  • calculates the aggregate of all possible export devices from his house, and deducts nothing for in-house use (it assumes there are no occupants because they’re away)
  • checks the size of the three-phase 440v cable feed from the substation. In his case that is 70mm² for the smallest part of the cable-run, which is quite adequate
  • checks the cable distance between his house and that substation, which is just short of 200m. From this the algorithm calculates the voltage rise which would occur at the Applicant Site when export is at maximum
  • checks the number of other properties between the Applicant Site and the substation. In this case it was 19 houses.

It is this last point which is most likely to constrain the maximum export which is permissible. 19 houses means that the Applicant Site will be sharing the same phase as 6 or 7 others. That’s not many.

So unless those 6 or 7 absorb the export power which Peter’s V2G charger is producing, then it will be evident at the substation. It would show as a phase-imbalance, which in turn creates losses within the transformer.

Once Kaluza’s Flex Platform is in widespread use, the problem can be overcome. It would be possible for Flex to turn on other devices within those neighbouring homes where the available energy could easily be deployed. An immersion heater or a Storage Radiator would be typical candidates.


The problem of losses due to phase imbalance is discussed more widely in the topic on the OpenLV Project for substation monitoring.