Using underground cables on a north/south electricity interconnector could increase costs five-fold, an independent report said.
The development is planned to link the grids of Northern Ireland and the Republic of Ireland to produce cheaper energy costs. Some residents on the route along the Monaghan-Tyrone border are unhappy at the prospect of new pylons being built across the countryside.
A report was announced by UK energy minister Charles Hendry on Tuesday.
"Overhead line is the cheapest transmission technology for any given route length or circuit capacity, with the lifetime cost estimates varying between £2.2 million and £4.2 million per kilometre," it said. The £4.2 million cost compares with up to £24.1 million per kilometre of underground cable.
The Electricity Transmission Costing Study is an independent report endorsed by the Institution of Engineering and Technology. It was commissioned by the Department for Energy and Climate Change in London and the National Grid.
Chairman of the project board, Professor Mike Sterling, said: "Naturally new electricity supply infrastructure, especially in sensitive areas of the country, is likely to be controversial and will be subject to detailed planning scrutiny.
"Any network reinforcement or new connection can take a number of different forms, the most common of which has been the use of overhead transmission lines, but other technical solutions exist. The costs of these solutions can, however, vary considerably, not just by small percentages but by multiples of the cheapest option."
Alternatives to overhead lines include burying cables in the ground directly, the next cheapest technology. Another option is a deep tunnel, which can cost up to £23.9 million per kilometre, depending upon the tunnel length. Longer connections are proportionately more efficient than shorter ones.
Earlier this month another report by three experts said using underground cables would see the cost of the north/south project rise from 167 million euros to 500 million euros. It also said that overhead cables could be made more attractive by spending more on new pylon designs rather than using the steel lattice towers which are currently proposed.
The report was commissioned by the Republic's energy minister Pat Rabbitte. A public planning inquiry into the Northern Ireland part of the project is due to begin in Armagh on March 6.