Report says that underground cables are still expensive

Underground power cables are still at least five times more expensive than overhead lines, new research says — despite advances in technology.

Burying underground cables (UGC) is the second-cheapest way of transmitting power but lifetime costs are £10.2m–£24.1m per km, compared to £2.2m–£4.2m per km for overhead lines (OHL), the government-commissioned report found.

The research, carried out by engineering consultancy Parsons Brinckerhoff and funded by National Grid, will disappoint campaigners who object to new electricity pylons and highlight the fact that new technologies are bringing underground costs down.

‘We still find, despite all the developments in technology, that overhead line is the cheapest way of providing a transmission connection in relevant places,’ said Mark Winfield, principal energy consultant for Parsons Brinckerhoff, at a press conference.

‘It’s not always appropriate to have overhead line but, where it is appropriate, it is the cheapest way of doing it.’

National Grid expects to build around 350km of transmission lines in the next 10 years. New cables will be needed as new power stations are built, particularly renewable energy plants in locations where there is no existing infrastructure.

The report, which drew on data provided by 24 power infrastructure companies and was scrutinised by the Institution of Engineering and Technology (IET), examined each transmission method in scenarios with different power capacities and route lengths.

It studied costs associated with building and maintaining power infrastructure over a typical lifetime of 40 years, as well as power lost as heat during transmission, but not social or environmental costs.

Other transmission methods studied included:

  • cables buried in a deep tunnel, which had lifetime costs of £12.9m–£23.9m per km;
  • underground gas-insulated line (GIL) technology, which is not used in the UK and had lifetime costs of £13.1m–£16.2m per km;
  • and 75km high-voltage direct-current (HVDC) connections, which had lifetime costs of £13.4m–£31.8m per km.

New technologies have brought down the costs of UGC, particularly in the last five to 10 years, said Winfield, although the build costs alone are still 10 times those of OHL.

For example, cable insulation made from crosslink polyethylene (XLPE) has replaced paper- and oil-based insulation because it is quicker and easier to manufacture and doesn’t carry the risk of oil leaking into the environment.

Overhead cable technology has also improved, however, and better-value conductors that can safely reach higher temperatures and so carry more current are now available, although not yet widely used in the UK.

The researchers also looked briefly at the new overhead pylon systems being considered by National Grid, said Winfield.

‘Our initial view is that the new type of overhead line wouldn’t be any cheaper and may be a little more expensive than the existing types, but that isn’t a fully engineered costing.’