More than 2,000 ESB customers have transferred to another supplier four months before the full opening up of the electricity market.

The customers are believed to have moved to green suppliers. The green or renewable market has been 100 per cent open since February 2000 and the ESB said yesterday that more than 2,000customers had already moved.

The company was outlining how the market-opening process, due to take place in February, is going to work. The company unveiled a new bill format, designed to give customers clearer information in relation to electricity usage and costs.

In the new system, ESB customers will remain with ESB Networks (which runs the electricity distribution system), but can chose their general electricity supplier. Mr Charles Chapman, ESB customer supply general manager, said: "The new electricity bill will allow our customers keep track of their spending on electricity, while at the same time allow ease of transfer between suppliers."

At a press briefing, ESB representatives acknowledged the company could lose revenue in the market-opening process. The ESB, unlike its competitors, will only be able to charge in line with rates approved by the Commission for Energy Regulation.

The company said the electricity market was opening two years ahead of a deadline set by the EU. The cost of the market opening will be €160 million and this will be paid by the whole industry. A software system from German firm SAP is expected to cost €30 million alone.

Meanwhile, the Department of Communications, Marine and Natural Resources said it was switching its electricity account to Energia, a subsidiary of Viridian.

Various Government departments are currently their electricity accounts. Some have moved to sign deals with green suppliers. Government contracts are small compared to others in the industrial segment of the market.