Underground or Overground –should we bury electricity cables?

The electricity transmission system in England and Wales consists of approximately 7,200 kilometres (4,470 miles) of overhead line and 1,400 kilometres (870 miles) of underground cable operating at 275,000 and 400,000 volts (275kV and 400kV). The term ‘undergrounding’ refers to the replacement of overhead cables with underground cables. When and where is undergrounding currently used – and should it be rolled out in more rural areas? Jessica Sellick investigates. ………………………………………………………………………………………………..

It was during the Industrial Revolution, and the work of Benjamin Franklin in 1752, which started the use of human-generated electricity. Coal was used to power tools and machines and, in 1769, James Watt patented the world’s first coal-powered steam engine which was used in factories and mills. The UK’s gas industry was founded in 1812 when Frederick Winsor formed a company to build a public gas works and distribute gas to customers through a network of underground pipes. London’s network provided gas to almost 70,000 streetlights by 1827, and in 1882 the Edison Electric Light Station was built in London to supply light and heat to urban residents.  

In the early 20th century electricity started to be pumped into people’s home using pylons designed by Sir Reginald Blomfield – with electricity being provided across the country. After the First World War the electricity industry wanted cheaper and more reliable energy supplies. In 1925 Lord Weir chaired a committee that proposed the development of the Central Electricity Board (CEB) which would connect power stations in Britain and be called a ‘national gridiron’. The Electricity (Supply) Act 1926 established the CEB as a statutory body with the duty of supplying electricity.  

The world’s first integrated national grid began in 1935, with 7 grid areas established and overseen by control rooms in Manchester, Leeds, Newcastle, Birmingham, Bristol, London and Glasgow. In 1937 control room engineers combined all seven grid areas for the first time. 

In the post first world war era power stations were being built less frequently, coal was rationed, yet electricity usage was increasing. In 1949 National Grid initiated talks with Électricité de France, a French-based power company, about constructing a cross-Channel power link. Still not able to keep up with supply demands, in 1950 a 12-year project was launched to establish a 275kV ‘supergrid’. 42-metre-high pylons and 4,000 miles of transmission lines were installed as part of this work. In 1957 the Central Electricity Generating Board (CEGB) was established – and its structure reduced to five regions to allow for more efficient operations. Between the 1960s and 1980s a new 400kV supergrid was constructed. 

In 1989 the Electricity Act was approved. This led to the privatisation of the electricity industry. Section 9 of the Act gave National Grid a statutory duty to maintain ‘an efficient, co-ordinated and economical system of electricity transmission’. National Grid also has to meet minimum standards of quality in terms of voltage and frequency; and is responsible for maintaining its transmission system and managing a programme of asset replacement. 

In 1995 National Grid was listed on the London Stock Exchange and its shares traded publicly. Its seven control centres across Britain were replaced by the Electricity National Control Centre (ENCC) in Wokingham. In practical terms National Grid transmits electricity at high speed (of 275kV and 400kV) across the country, through pylons and overhead lines, and then transports electricity into homes and businesses through its distribution networks. To make the electricity safe for domestic use National Grid must lower the voltage of electricity to up to 132kV– which can be done via smaller pylons or underground cables that carry lower voltage lines. In addition, small-scale electricity generators (e.g. wind farms, solar parks) connect direct to the distribution network through embedded generation. In 2019, for the first time in the UK and the United States, more energy was generated from zero carbon sources than fossil fuels and the National Grid launched ‘The Great Grid Upgrade’, infrastructure projects to connect more renewable energy to homes and businesses.

In England and Wales National Grid owns, builds and maintains pylons and overhead lines (OHL) and underground cables that make up the electricity transmission network. Distribution network operators (DNOs) manage the poles, pylons and cables in a local area – in some local areas these are also run by the National Grid while in other areas other operators manage the network.  

What is undergrounding – and when and where is it used? Undergrounding is a process whereby overhead lines (OHLs) providing electrical power or telecommunications are replaced with underground cables. The technology to do this ranges from direct burial (1.5 metres wide and 1.2 metres deep) through to deep bore tunnels (12 metres wide and 25-30 metres deep). 

Early undergrounding can be traced back to the first submarine communications cables laid in the 1850s which carried telegraphy traffic, with the first transatlantic telegraph cable becoming operational on 16 August 1858. Around 1890 Sebastian Ziani de Ferranti designed high-voltage underground mains cables which he used to connect the Grosvenor Galleries to Deptford substation – he further developed this cabling so they could handle 10,000 volt current to be rolled out more widely. During the 20th century Direct-buried cable (DBC) became commonplace. Unlike standard power cables, which have a thin layer of insulation and a waterproof outer layer, DBC consists of multiple layers of heavy metallic-banded sheathing, reinforced by rubber covers, shock absorbing gel, waterproof tape and stiffened by a heavy metal core. 

The security and reliability of the UK’s current and future energy supply is dependent on having a network and infrastructure to meet electricity demand – this includes above and lower voltage OHL and underground cables of any voltage. The Department for Energy Security and Net Zero (DESNZ) publishes planning guidance for developers of nationally significant energy infrastructure projects. Overarching National Policy Statement for energy (EN-1) was presented to parliament in November 2023 and came into force in January 2024. Section 5.10.7 states: 

National Parks, the Broads and AONBs have been confirmed by the government as having the highest status of protection in relation to landscape and natural beauty. Each of these designated areas has specific statutory purposes. Projects should be designed sensitively given the various siting, operational, and other relevant constraints. For development proposals located within designated landscapes, the Secretary of State should be satisfied that measures which seek to further purposes of the designation are sufficient, appropriate, and proportionate to the type and scale of the development. 

Section 5.11.20 states: 

The general policies controlling development in the countryside apply with equal force in Green Belts but there is, in addition, a general presumption against inappropriate development within them. Such development should not be approved except in very special circumstances. Applicants should therefore determine whether their proposal, or any part of it, is within an established Green Belt and if it is, whether their proposal may be inappropriate development within the meaning of Green Belt policy. 

DESNZ’s National Policy Statement for electricity networks infrastructure (EN-5) was published in November 2023. This sets out the Government’s policy on OHL and underground cables. Sections 2.9.11-12 state: 

Landscape and visual benefits may arise through the reconfiguration, rationalisation, or undergrounding of existing electricity network infrastructure. Though mitigation of the landscape and visual impacts arising from overhead lines and their associated infrastructure is usually possible, it may not always be so, and the impossibility of full mitigation in these cases does not countermand the need for overhead lines…However, in nationally designated landscapes (for instance, National Parks, The Broads and Areas of Outstanding Natural Beauty) even residual impacts may well make an overhead line proposal unacceptable in planning terms. 

Sections 2.9.20-23 state: 

Although it is the government’s position that overhead lines should be the strong starting presumption for electricity networks developments in general, this presumption is reversed when proposed developments will cross part of a nationally designated landscape (i.e. National Park, The Broads, or Area of Outstanding Natural Beauty)… However, undergrounding will not be required where it is infeasible in engineering terms, or where the harm that it causes (see section 2.11.4) is not outweighed by its corresponding landscape, visual amenity and natural beauty benefits…Additionally, cases will arise where – though no part of the proposed development crosses a designated landscape – a high potential for widespread and significant adverse landscape and/or visual impacts along certain sections of its route may result in recommendations to use undergrounding for relevant segments of the line or alternatively consideration of using a route including subsea cabling. 

These documents set out the factors that the Secretary of State should consider in granting development consent, including:

  • The landscape and visual baseline characteristics of the setting of the proposed route. 
  • The additional cost of the proposed underground or subsea alternatives, including their significantly higher lifetime cost of repair and later uprating. 
  • The applicant’s commitment to mitigate the potential detrimental effects of undergrounding works on any relevant agricultural land and soils (including peat soils). 

Overall, OHL is the Government’s strong starting presumption for electricity network infrastructure developments. However, this is reversed in nationally designated landscapes where the strong starting presumption should be that the applicant will underground ‘relevant sections’ of the line. 

The Visual Impact Provision (VIP) is managed by National Grid and administering £465 million of funding from Ofgem to reduce the impact of existing transmission lines in English and Welsh AONBs and National Parks. The National Grid has  assessed 571km of its electricity transmission lines in these protected landscapes to identify which sections have the highest visual impact on their surroundings. Using input from technical experts, local stakeholders, communities and a Stakeholder Advisory Group, 4 individual priority schemes have been selected where replacing the OHL with an underground connection could have a transformative effect on the landscape: (1) Cotswolds, (2) Dorset, (3) Snowdonia, and (4) North Wessex Downs. Alongside this, the VIP project includes the Landscape Enhancement Initiative (LEI) which is a grant scheme which awarded almost £4 million between 2015 and 2021 for localised visual improvement projects. From 2022 National Grid intends to make £11-12 million available over a 5-year period to National Landscapes  and National Parks in England and Wales.  

What are the benefits of undergrounding? Back in 2015 the National Grid published a technical report on undergrounding high voltage electricity transmission lines. This looked at the technical merits and challenges associated with underground lines compared to installing overhead lines. While costs will vary depending upon length, power, voltage, and ground conditions; the operation, maintenance, and energy losses over the life of the connection are broadly the same for undergrounding as for overhead lines. The report found ‘The use of underground cables has a long-term positive visual impact when compared with the use of overhead lines, and in some instances this will be the preferred choice’ (page 8). 

Given the future pipeline for NSIP projects will consist of significant numbers of energy projects coming forward, the Government consulted on an updated suite of energy NPSs. In November 2023, the Government published the consultation response to planning for new energy infrastructure. On the presumption for OHL except in nationally designated landscapes, some environmental organisations commented that this should be expanded to all biodiverse areas, including those adjacent to nationally designated areas. Similarly, a few local government respondents called for the presumption to be expanded to areas of local or historic value. They suggested these areas could equally benefit from the starting presumption and their lack of inclusion risked damaging the local character, biodiversity, and value of these areas. Some members of the public and local authorities expressed concern about the visual impact of OHLs, describing them as ugly and/or a blot on the landscape. Some respondents described: 

  • OHL as being highly damaging to habitats and bird strikes into power lines as being a major killer acknowledged in the national policy statements. 
  • OHL as being less resilient in extreme weather than underground cables or sub-sea grids. 
  • OHL causing significant damage to landscape, archaeology and cultural heritage including the settings of AONB (even when the pylons are outside of the AONB), scheduled monuments and listed buildings. 
  • How forcing pylons upon communities without genuine alternatives is not fair. 

For national landscapes and national parks, the selection criteria for awarding LEI funding takes account of: 

  • The reduction of existing electricity transmission infrastructure on publicly accessible viewpoints, and general visual resource experienced by local communities and/or visitors to the area. 
  • Helping to foster regional and local landscape diversity and distinctiveness (informed by Natural England’s National Character Area profiles).  
  • The other environmental benefits the project will bring – such as protecting or enhancing biodiversity and/or historic features. 
  • The contribution to sustainable social and economic development in the area. 

What are some of the challenges? Underground has other financial, environmental, and socio-economic factors that should also be considered. 

  • Transmission lines intended for open-air use are not suitable for burial underground as they produce heat that cannot dissipate through soil. This means underground lines must be insulated, adding additional expense. Some studies indicate that the cost to install the same length of wire underground can be 10 times more than the equivalent work above-ground. For example, a study from the Institute of Engineering and Technology (IET) and Parsons Brinkerhoff published back in 2012 found OHL was the cheapest transmission technology for any given route length or circuit capacity, with the lifetime cost estimates varying between £2.2m and £4.2m per kilometre. This compares to lifetime cost estimates varying between £10.2m and £24.1m per kilometre for underground cable direct buried; and to £12.9 million to £23.9 million for undergrounding using a deep tunnel. National Grid’s technical report found to match overhead line thermal performance for a 400kV double circuit, as many as 12 separate cables in four separate trenches may be needed if undergrounding, resulting in a work area up to 65 metres wide. 
  • Underground wires have a shorter lifespan than their above-ground counterparts. This is a result of corrosion. Indeed, there are already a limited number of cable manufacturers across the world particularly for cables at the high voltages required by National Grid. 
  • Routine maintenance is more difficult, and service restoration can take longer as it can be harder to pinpoint the exact location of the interruption. 
  • Repairing faults can take longer due to the excavation necessary to make the repair, after which the area must be re-landscaped and restored to its previous state.
  • Environmental impacts result from undergrounding cables – this can pose a threat to sensitive and protected species and habitats and potential damage to archaeological heritage. 

Should more undergrounding take place in rural areas? The Government has not laid down any further rules on the circumstances requiring the use of undergrounding, therefore, the secretary of state must weigh the feasibility, cost, and any harm of the undergrounding against: 

  • The adverse implications of the OHL proposal. 
  • The cost and feasibility of re-routing OHL or mitigation proposals for the relevant line section. 
  • The cost and feasibility of the reconfiguration, rationalisation, and use of underground cabling of proximate existing or proposed electricity networks infrastructure. 

The secretary of state should therefore only grant development consent for underground sections of a proposed line over an overhead alternative if they are satisfied that the benefits accruing from the former proposal clearly outweigh any extra economic, social, or environmental impacts that it presents, the mitigation hierarchy has been followed, and that any technical obstacles associated with it are surmountable. While arguments in favour of undergrounding were seen in response to the Government’s consultation on draft national policy statements for energy infrastructure, the starting presumption remains for OHL with the exception of nationally designated landscapes. 

Where next? The IET and Parsons Brinckerhoff study concluded that ‘no one technology can cover, or is appropriate in, every circumstance, and thus financial cost cannot be used as the only factor in the choice of one technology over another in a given application’. On 22 November 2023, Claire Coutinho, the Secretary of State for Energy Security and Net Zero announced a new programme to deliver transformation of the electricity network. This includes plans to halve the time it takes to build new transmission infrastructure, to reduce the time taken for viable projects to connect to the grid, to introduce a community benefits package for communities who host transmission infrastructure, and to run a national communications campaign to improve public understanding of electricity infrastructure and its benefits. The Government is proposing a package whereby local communities will receive around £200,000/km (~£320,000/mile) for overhead lines, £40,000/km (~£60,000/mile) for underground cables, and £200,000 per substation. It will be for the local community to decide in consultation with the developer what projects they would like to support. No specific references were made to undergrounding or to rural communities. How will rural communities be involved in the design, development, and delivery of future electricity infrastructure – and how much undergrounding do we want to see in the countryside? Watch this space. 

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Jessica is a project manager at Rose Regeneration and a senior research fellow at The National Centre for Rural Health and Care (NCRHC). She is currently evaluating a service that supports older people to maintain their independence; and reviewing neighbourhood-based initiatives (NBI). Jessica also sits on the board of a charity supporting  rural communities across Cambridgeshire and is a member of her local Patient Participation Group. 

She can be contacted by email jessica.sellick@roseregeneration.co.uk. 

Website: http://roseregeneration.co.uk/https://www.ncrhc.org/ 

Blog: http://ruralwords.co.uk/ 

Twitter: @RoseRegen