The number of "amber alerts" warning of potential shortages in the electricity system have doubled to 50 so far this year, new figures show.

It has also emerged that the Republic suffered a more serious "red alert" last August when the danger of a serious shortage of power increased after a series of technical problems developed.

An "amber alert" is when the system has only approximately 400 megawatts of power in reserve, the equivalent of one large gas-fired station.

A red alert indicates an even smaller reserve. The alerts warn suppliers of power to the national grid to act with caution.

The figures supplied by members of the industry highlight the challenge ahead for the national grid to manage supply and demand, particularly this January.

The peak period of electricity consumption normally occurs between 5pm and 7pm, and supply is likely to be very tight at this time of the day during January.

Cold weather, especially snow, puts huge pressure on the system.

In the whole of 2004 there were 25 amber alerts, but no red alerts. The system then benefited from peaking or emergency capacity shipped into the State by the ESB.

However, since then, demand has risen again, mainly because of new housing estates, many of which are on the outskirts of Dublin.

Industry is also increasing its consumption, although an energy conservation project has managed to improve the situation.

According to figures from the Committee on Energy Regulation, demand for electricity peaked at a record 4,700 megawatts at 5.30pm on November 28th.

The system managed to meet this demand, but it needed the 238 megawatts of wind energy and another 108 megawatts of energy from the interconnector with Northern Ireland.

Some industry sources working with power plants have claimed that, in order to balance supply and demand, "load shedding" - cutting off certain parts of the country for short periods to balance the energy supply - has occasionally occurred.

An ESB spokesman yesterday refused to comment on this.

This week the Minister for Communications, Marine and Natural Resources, Noel Dempsey, said supply remained tight though he believed the addition of two new stations - at Tynagh and Aughinish Alumina - would help to address this problem.

The Tynagh plant, the larger of the two, is expected to become operational next year. This will provide up to 400 megawatts of power.

One of the shareholders in the this project, Gama Construction, is currently trying to sell some or all of its 80 per cent stake in the station.

Another power station is also on the way with Viridian planning a second plant at Huntstown, north Co Dublin.