The ESB's main rival, Viridian, has won a major contract to supply electricity to three Government departments, including the department responsible for the future of the ESB.
Under the €6.1 million contract, Energia, the electricity supply arm of Viridian, will provide power to over 100 Government offices, including the Department of Communications, Marine and Natural Resources.
Offices within the Department of Social and Family Affairs and the Department of Enterprise, Trade and Employment are also covered by the deal.
The contract was awarded under a competitive tendering process by the Office of Public Works.
Energia's sales and marketing director, Gary Ryan, welcomed the decision as part of what he said was a growing trend by the public sector to seek out competitive electricity packages.
In May, Energia won a €1.7 million contract to supply power to 150 Garda stations throughout the State. It also provides power to some State agencies, local authorities and other public sector organisations.
On an all-island basis, Energia has a 25 per cent market share of the corporate electricity market. It has offices in Dublin, Cork, Galway and Belfast.
It sources power from the Viridian Group's power station in Huntstown, north Dublin. The group is currently investing in a second power plant in Dublin, which will bring its investment in the Republic to €500 million.
Viridian Group, which also owns Northern Ireland Electricity, Huntstown Power and Powerteam Electrical Services, is listed on the Dublin and London stock exchanges and has a market capitalisation of around £1.1 billion (€1.6 billion).
Minister for Communications, Marine and Natural Resources Noel Dempsey last week told an Energy Ireland conference in Dublin that the Irish energy sector needed more competition to deliver better choice and innovation to consumers.
Mr Dempsey said the ESB should not be broken up but that some structural reforms were needed for the semi-State company.
The Minister said the Government recognised the "strategic value" of maintaining the ESB as a strong and commercially viable entity.
