Most countries go for overhead system – apart from Germany
IRELAND is not unusual in erecting the vast bulk of its high-voltage power lines overground.
Pylons rising up to 45 metres into the air are common across most of Europe, and experts believe that most new projects will remain overground for the foreseeable future because of the technical difficulties and cost of building them below the surface.
Europacable, which represents wire and cable manufacturers, says the maximum length of high-voltage cable that can be placed underground is about 20km.
Some countries, including the Netherlands and Germany, are engaged in pilot projects to use underground technology – where it must be considered when it passes close to individual homes or settlements.
Denmark has committed to sinking lower-voltage cables as new lines are delivered and older ones upgraded. But on the issue of 400kv lines – the ones at the centre of the current controversy – Denmark has only committed to exploring placing them underground when the technology allows it.
Sections of line will be sunk, but most of the line will remain visible.
In general, lines are built in trenches in urban areas. In Japan, the vast majority of its electricity power cables are over ground, and the country's ministry for construction and transport says the main factors involved in using overhead lines are cost and the ease with which they can be repaired.
This has proved crucial in the past following natural disasters such as earthquakes and tsunamis.
In Tokyo, more than 90pc of power cables are overhead and of the cables that are underground, less than 1pc are in the super-high voltage range of between 315kV and 500kV.
This is in stark contrast to the approach taken in central London, where everything goes underground.
There is a £1bn (€1.2bn) project to create a 32km electricity superhighway under London.
UK National Grid spokesman Stewart Larque said: "The underground cables get used in the specifically sensitive areas, areas of particular beauty or central London, where you have no other option."
Three-quarters of the high-voltage lines constructed by National Grid over the past three years have been overhead lines, with some exceptions. The Hinkley Point connection linking to a nuclear power station in the south-west of England will involve 8km of the 57km line going underground. The Mid Wales Connection, linking up wind farms in central Wales, is set to involve 13km of the 53km-line being routed underground.
The planning system also differs in EU member states. In Italy, just one process is completed by the developer which deals with deciding environmental concerns, granting permission and issuing permits for operation.
In Germany, two processes must be completed including identifying the route, which is decided by a regional authority, followed by plan approval which results in the issuing of a permit to build and operate the project.
There are seven processes in Hungary, which can lead to lengthy delays, while in England and Wales the process takes about 12 months.