Changes to the power grid system could cost "many millions of pounds" in transmission constraints, the national grid operator has claimed.
EirGrid, which is to be formally separated from the ESB this year, made its concerns known in a paper sent last week to the electricity regulator, Mr Tom Reeves.
He has proposed changing the grid connection system, requiring EirGrid to provide full access to the network to whichever groups required it. Such access is not available to all at present, due to constraints on the transmission system.
The EU Competition Commissioner, Mr Mario Monti, is believed to have told the Minister for Public Enterprise, Ms O'Rourke, that implementing this change will be crucial to the market's liberalisation.
However, EirGrid told Mr Reeves that such changes have potential "to greatly increase the level of regulatory risk faced by market players, which may not be conducive to competition".
Without grid connections, power generators cannot supply electricity into the network.
Only two groups which plan new power stations have secured "deep" grid connections for their plant.
They are Viridian, the former state monopoly in the North; and the ESB, whose joint venture with Statoil secured its connection before the market was partly liberalised last February.
Another group, Ireland Power, has secured only a "shallow" connection. It is backed by a US businessman, Mr Larry Thomas, in addition to the British-based energy multinational, BP, and ePower, a Dublin firm controlled by Esat's founder Mr Denis O'Brien.
This group would secure a "deep" system connection under the new arrangement proposed by Mr Reeves.
The ESB, however, has "grave concern" about the plan. It told Mr Reeves the new arrangements would discriminate against its legitimate interests.
In Mr Reeves's plan, EirGrid would transmit power from generators according to "economic precedence". This could mean older ESB generation plant is used only when newer plant operated by its competitors was at full capacity.
EirGrid's submission said: "We are particularly concerned at the cost implications and possible planning and development implications of the proposed changes."
It added: "The approaches referred to in the accompanying letter could lead to a fundamental change in the existing trading arrangements and tariff regime and also result in a significant increase in the level of complexity, uncertainty and risk facing generators, suppliers and the Transmission System Operator [i.e. EirGrid]."
While two other options could promote competition with less impact on the existing market rules and tariff design, EirGrid said it should not be assumed that it was proposing or supporting change in the existing regime.
An action by ESB Independent Energy against Mr Reeves is due before the High Court this morning. The subsidiary is challenging a direction by Mr Reeves who said it was insufficiently ringfenced from its parent.
