Siting studies- how do we locate new assets?

As the high voltage electricity network owner for England and Wales, National Grid Electricity Transmission has recently seen a significant increase in connection applications. This shift in volume has meant greater numbers of required network reinforcements have been triggered, including new assets potentially planned across our network to accommodate connections.

Under current processes, if a new asset is triggered, several steps must be followed. Firstly, since applications are currently handled on a first come first serve basis, applications which trigger new assets are assessed according to the order in which they apply. If a new application were to be submitted now, we could not assess its connection date or locations without considering those connections which come before. If certain connections do not come to fruition and are reviewed under proposed reform measures currently underway- dates and connections could change. This might mean proposed new substations may not be built- or could change location and size depending on identified network needs. This means that siting studies for new substations cannot begin immediately upon application submission- until clarity of connections and network requirements are confirmed. Further information is shared with relevant customers when it is available directly through the connections process.

Siting studies themselves must encompass a variety of factors. They seek to assess the best possible outcome, assessing both wider network needs and the requirements of any connections. The most economic and efficient option both for the end consumer and our direct customers is balanced against the need to protect the environment and geographical considerations.

Some of the areas we might consider in our siting studies are:

Location of the new asset

Solutions could look very different depending on the specific part of the network the new asset is needed in.

Chesterfield substation
Air insulated substation

For example, a new site in a more populated area might need to be smaller and quieter, so a gas insulated substation might be considered.

For larger areas or more isolated industrial locations, an open-air insulated substation could be a more economic option. 

For more information on different insulation and asset configurations, read our article on the different types of substations we have on our networks.  

Projected demand

When assessing options for a new site, we account for the current and projected demand in a region. If there is a predicted increase in demand, or a trend of increase in connection applications, a new site will consider the need for future expansion, either by increasing the number of bays, or adding land to extend in future. Locations might also need to provide space for Grid Supply Points to bring power into the local District Network Operator's  (DNO) systems- which can then be provided directly into homes and businesses. 

Existing Infrastructure

The location of existing circuits and equipment is also assessed, to minimise the length of additional infrastructure required- further ensuring the option chosen is the most economic and efficient available.  Options will ideally be within 2km of an existing circuit to prevent the need for a new Development Consent Order (DCO)- which would add additional time and resource. Overhead line diversion or additional transmission towers may need to be considered depending on the location- which also require their own assessment for best possible placement from a visual, environmental, and cost perspective. The Holford rules for overhead line construction further establish our requirements for the routeing of any additional infrastructure. 

Geographical considerations

Characteristics of the land are crucial to the safe and sustainable build of a substation. Land that is prone to floods cannot be considered, or land that is boggy in nature. Equally, land subject to subsidence, or with general soil issues cannot be considered. Topographically, the flatter the land the better- as hills or valleys can make constructing equipment difficult and requiring equipment of all different heights to retain safety distances. The site must also be accessible by foot and vehicle, for maintenance and emergency attendance. 

Environmental, cultural, and visual considerations.

These form some of the most extensive considerations when assessing the best location for a new asset. There are several guidelines we adhere to during the siting studies, including the Horlock rules. These rules ensure that we consider many varied factors, including visual aspects:

‘The siting of substations, extensions and associated proposals should take advantage of the screening provided by landform and existing features.’                     

This means that wherever possible, we will seek to mitigate the visual impact of our assets using the natural features of the landscape. We will also account for land which is culturally important:

‘Siting… should as far as reasonably practicable seek to avoid altogether internationally and nationally designated areas of the highest amenity, cultural or scientific value.’

Searching for insects
Assessing insect populations

This includes any historically or culturally significant areas, as well as national parks and other priority locations. 

Environmental studies also form a key cornerstone of our siting, and we seek to avoid or mitigate any environmental impacts from our activities. The Horlock Rules state that:

‘In the development of new substations, consideration must be given…to balance the technical benefits and capital cost requirements for new developments against the consequential environmental effects… to keep adverse effects to a reasonably practicable minimum. 

Important existing habitats and landscape features including ancient woodland, historic hedgerows, surface and ground water sources and nature conservation areas should be protected as far as reasonably practicable.’     


We must conduct extensive species studies on any land identified, and ensure the habitats are well understood- accounting for any protected characteristics and assessing mitigating measures like providing alternative habitats. For more information on what we do to ensure we prioritise protection of the environment in our development activities, read our article here. 

Connections Reform

We are working alongside industry to reform the connections process- and move towards a more strategic network investment approach, meaning the consideration of siting studies and plans for new assets could change. For more information please visit our Connections Reform page.