The Energy Star labelling scheme for energy efficient PCs will receive its first revamp since 2000 this week with the introduction of a raft of stringent new standards that will ensure three quarters of PCs in the market no longer qualify for the label.

The previous version 3.0 specifications had simply required PCs to use less than 20w/h when in sleep mode to qualify for an Energy Star label. However, subsequent developments in PC energy efficiency meant that the label had become devalued in recent years with 98 percent of PCs on the market estimated to qualify under these criteria.

The US Environmental Protection Agency (EPA) unveiled plans to tackle the problem late last year with a revamped set of more stringent standards that address a wider range of performance criteria. The EPA said at the time that these new standards, which come into effect this Wednesday, should ensure that just the most energy efficient 25 percent of desktop PCs qualify for the label.

Catriona McAlister, senior consultant at environmental consultancy AEA and a contributor to the Energy Star initiative, said that early indications showed that the EPA was set to achieve its goal. "An analysis of the EU Energy Star database has shown that the specification is currently on track to qualify [just a quarter] of models on the market," she said.

Central to the updated specifications is a new requirement that Energy Star-qualified PCs have a power supply boasting 80 percent efficiency. Corrinna Kammerer, desktop and green PC manager at Fujitsu Siemens Computers, said that power supply units with 80 percent efficiency were now widely available, but they did come at a price premium and as a result many PCs currently in the market only boast efficiency of around 65 percent.

The new standards also introduce more stringent specifications for system power consumption, requiring qualified PCs to use no more than four watts in sleep mode and 2 watts in stand by mode. A sliding scale of requirements for energy consumption when the system is idle has also been introduced meaning that low end single core CPU machines must use no more than 50 watts; mid-range multi-core CPU systems with 1GB memory must use no more than 65 watts; and high-end gaming PCs boasting graphic cards and other power hungry components must use no more than 95 watts.

The EPA said that compliance with these new standards will mean that the average Energy Star labeled PC will consume 65 percent less energy than conventional models.

Energy Star labeled products are expected to carry a small price premium, according to Kammerer, with prices for qualified machines expected to be €10 to €20 higher than conventional alternatives. However, industry estimates suggest qualified models could save firms up to £10 a year on their energy bills meaning that the extra up front cost will be offset within a year to 18 months.

John Madden of analysts Ovum predicted many customers would use the Energy Star label as a factor in purchasing decisions. "Once these rules are implemented and people see the standards have some teeth I could see it becoming one of the top three or four factors in [purchasing] decisions," he said.

As a result the proportion of Energy Star labeled PCs is expected to increase rapidly over the next few years as more vendors look to gain a green stamp of approval for their PCs. "All the big brands are already offering Energy Star 4.0 compliant models and with customers likely to just cut and paste current requirements for Energy Star kit into new tenders there will be customer pressure to offer more Energy Star qualified options," said Kammerer. "We will see more and more new models meet the standards."

However, the EPA appears to have learnt from its mistakes and is planning to guard against the label being devalued by technology improvements again with a stricter version 2 of the 4.0 standard already scheduled for 2010.