New figures reveal that, in 2005, there were 57 'amber alerts' . . . an internal signal to generators that electricity demand is coming uncomfortably close to meeting supply. And natural resources minister Noel Dempsey has confirmed that the "margin between capacity and demand for electricity is tighter than normal this winter".

Two new private sector plants are due to bring an extra 500 megawatts of power into the grid this spring, while construction has begun on a 400MW plant in north Dublin.

The should ensure a more comfortable margin between supply and demand over the next couple of winters.

However, with ESB likely to be restricted from building new generating plants because of its dominant market position, Green TD Eamon Ryan says there are no new plants on the horizon after those three.

With demand continuing to grow, he warned that by 2008 or 2009, there was a "very real possibility" of blackouts unless more new capacity is added.

This was confirmed by a union source who said that, "with things so close to the wire", nobody in the energy sector would deny there was a fear of future blackouts.

Dempsey has expressed concern about the performance of older ESB generating plants. There are widespread claims that special mobile generators brought in to provide emergency back-up are being used almost daily to prop up performance.

Latest figures show an average plant availability rate of around 82%, which is considerably less than the international norm of 90%. It is also understood that, at times, almost 25% of generating capacity has been out or unavailable.

Demand for electricity, driven by the booming economy, has continued to grow at record levels. A new demand high of 4,823MW was set on 13 December. Although total capacity is now 6,000MW, with close to one-fifth of plant unavailable, there is little margin for error.