Denis Naughten (Roscommon-Galway, Independent) | Oireachtas source

I am told the only feasible way to underground a circuit with 1,500 MW capacity over a distance of 138 km is to use a specialised high-voltage direct current with conversation equipment at either end, not AC technology. For a DC link to act reliably with a synchronous network, it would be necessary to develop new and complex control systems that have not been tried before in order to replicate the functionality of an AC interconnector. I am told that it is not the same as undergrounding in regard to some other projects. The example that has been given in the past is the Aachen to Liege project, where there was undergrounding, but over a much shorter distance and with a lower capacity. If we take the cost of that project based on the bigger scale that is required here, the DC undergrounding cable option as applied there would cost in the region of €992 million, which is significantly higher than what is projected here. The argument is made by EirGrid, based on its research, that the underground option would be three times more expensive.

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