The East-West Interconnector linking the power grids of Ireland and Britain has been officially opened.
The interconnector is around 260km in length and has the capacity to carry 500 megawatts of electricity between Ireland and Britain, which is enough energy to power 300,000 homes.
It is the largest single piece of energy infrastructure to be built in Ireland since the Ardnacrusha Hydroelectric Power Station was opened in 1929.
It will allow electricity to be bought and sold between the two countries.
Minister for Communications, Energy and Natural Resources Pat Rabbitte said he is hopeful that the interconnector could lead to cheaper electricity for consumers.
He said: "The entire thrust behind the integration of European markets, of which this is a leading example, is to produce more competitive energy for consumers and for business."
Eirgrid, which was in charge of delivering the project, said it had come in on time and below its €600m budget.
Its chief executive Dermot Byrne said the interconnector is transformational and the benefits will continue to flow for many years.
He said the interconnector creates a security of supply for Ireland and will also place a downward pressure on prices.
The interconnector will begin commercial operations on 1 October. It runs between Deeside in north Wales and Woodland, Co Meath.
Today's event in Meath was also attended by Taoiseach Enda Kenny and EU Energy Commissioner Günther Oettinger.
Mr Oettinger said: "The East-West Interconnector represents a very good example of cross-border integration of energy markets.
"It is a milestone in the continued efforts by Ireland to develop its electricity grid and to respond to changing markets and opportunities."