CASE STUDY: Europe’s first upgrade of a medium-voltage transmission line from AC to DC overcame limitations integrating Anglesey renewables

Offshore windfarm, Skegness. This picture probably shows the "Lynn" part of the Lynn and Inner Dowsing Wind Farm. The three stumps which can be seen behind the six turbines are probably foundations for the Lincs Wind Farm, for which construction began in 2011.

One of the best options for reducing UK carbon emissions is through increased use of offshore renewable energy sources.

However, transporting electricity over long distances can result in significant losses.

DC (direct current) transmission is much more efficient than AC (alternating current) over long distances but requires careful integration with the existing AC grid.


Anglesey has significant renewable energy resources, particularly from wind, which could benefit the rest of Wales.

There was an existing AC transmission line between the Isle of Anglesey and mainland Bangor, which was seldom used because of loading issues and the way the network was operated.

By providing simulation studies, models, and technical recommendations, researchers from Cardiff University helped secure a £13.5m investment from Ofgem, with a further £1.5m from SP Energy Networks, to convert the existing but mostly-idle AC line to medium-voltage direct current (MVDC).

This overcame limitations of integrating renewables from the Isle of Anglesey to the mainland, and led to:

  • Carbon emission savings of 128 tonnes a year (worth £20m in carbon benefits).
  • 23% increase in transmission capacity, with £18m worth of economic energy savings predicted over the next 30 years.
  • 200 full-time equivalent jobs created locally between 2016 and 2020.


It can be difficult to integrate new renewable technologies into the UK’s existing infrastructure.

This is because much of it is decades old and was designed to transfer power to consumers from large, centralised power stations rather than smaller distributed generators.

Upgrading existing AC links to DC will reduce the amount of electricity that is lost during transport to our homes and businesses and make offshore renewable energy generation more efficient.


Based on the success of this project, SP Energy Networks anticipated that a further 25 projects across the UK could be investigated, bringing about significant economic and carbon benefits.

For more information about this project and those involved, visit: