The only thing that can be said with certainty about EirGrid’s two plans to develop high-capacity power connections to the Republic’s west, south and southwest, is that they have become, at best, medium-term projects.

Initially the State electricity network company seemed to be ploughing ahead with the overground option – hundreds of kilometres of 440kV cables and many hundreds of enormous pylons connecting the east to northwest Mayo and the east to the southern seaboard from Wexford to Cork.

The appointment of a commission to oversee the process has changed the dynamic. The Government-appointed commission, chaired by retired Supreme Court judge Ms Justice Catherine McGuinness, will not be the final arbiter on choosing the route but will ensure the alternative options are scoped as thoroughly and comprehensively as the overground options. The final decision-makers will be the company, the energy regulator and An Bord Pleanála.

The Grid West project is at a more advanced state than the Grid Link project running from Kildare to Cork. Hence the earlier publication of its preferred underground route.

This was published yesterday and involves a 113km route from Flagford in Co Roscommon to Moygownagh in northwest Mayo. The route follows a line similar to that of the overground options, with a preference for following secondary rather than primary roads (as it involves less disruption during construction and maintenance).

The work involved in undergrounding is relatively straightforward. Trenches are dug and cables and surrounding ducts are laid before the road is backfilled. In some places the condition of the road is relatively poor and in those stretches the foundation of the road will also be strengthened.

EirGrid chief executive Fintan Slye told The Irish Times yesterday: "We now have an underground option assessed to the same level of detail as the overground route option." He said this showed EirGrid was "listening and responding to the feedback that we got in the latter half of last year and first part of this year, and coming up with an analysis and process".

The underground option will be analysed by EirGrid on a large number of grounds, including engineering, design, environment and cost.

The big and as yet unanswered question is the cost. If, as expected, the underground costs are a multiple of overground it's going to be a hard sell. Some interested parties such as local MEP Marian Harkin are already emphasising the need for commensurate consideration for other factors such as scenic beauty and environment in efforts not to make cost the overriding issue.

What could be the most likely outcome is a hybrid option. That would involve an overground system but with key sections being put underground. Current technology would allow stretches of between 7km and 10km. It might not be an ideal solution but it might be persuasive on grounds of costs, with the most scenic areas getting the benefit.

The commission will assess EirGrid’s analysis of the underground route to ensure it is as comprehensive and thorough as the company’s assessment of the overground option. That is not likely to take place until the end of the year. After that there will be a period of consultation before a decision is made and the regulator and An Bord Pleanála get involved.

A similar exercise will be required with Grid Link. The establishment of the commission effectively removed the pylon issue to a large extent from the local electoral agenda. Autumn 2015 looks like decision time.

The timing of that might be key as it could coincide with the opening shots of a general election campaign.