An area in which the island operate as a single market is electricity . For much of their existence electricity networks in the Republic of Ireland and Northern Ireland was entirely separate . Both networks was designed and constructed independently post partition . However , as a result of changes over recent years they are now connected with three interlinks and also connected through Great Britain to mainland Europe . The situation in Northern Ireland is complicated by the issue of private companies not supplying Northern Ireland Electricity ( NIE ) with enough power . In the Republic of Ireland , the ESB have failed to modernise its power stations and the availability of power plants have recently averaged only 66 % , one of the worst such rates in Western Europe . EirGrid is building a HVDC transmission line between Ireland and Great Britain with a capacity of 500 MW , about 10 % of Ireland 's peak demand .