New England’s grid operator should closely monitor new combined cycle power plants which performed poorly during the past 2 years, according to new analysis of the region’s power plant availability.

ISO New England Inc., Holyoke, Mass., initiated the study in August 2000 to determine the causes of an increase in outages during early 2000. Separately, the ISO and the Massachusetts attorney general are investigating whether market power was exercised in the region by comparing marginal costs of energy production with wholesale clearing prices.

Seven new combined cycle units recently entered service, almost doubling to 4,957 Mw New England’s resources of this type. The ISO study found the new plants were generally larger, with five being larger than 200 Mw, but performed less reliably than the 20 units built earlier.

Last year only one of the new plants had an availability factor greater than 81%, and only one of the old units had an availability index of less than 81%. Those entering service before 1999 had an average availability index of 89%, while those coming on line after 1999 had an average availability index of 63%.

The report noted combined cycle units have become popular because their capital costs per kilowatt are low compared to conventional steam units, they are more efficient than straight-through combustion turbines or conventional steam units, they burn gas cleanly and are relatively easy to permit, and they can be built quickly.

However, since the new and old technology differ the new plants appear to be experiencing a debugging period “characterized by high forced outages or deratings,” the report said. In one case, an operator reported spending or budgeting $8 million in capital improvements and system redesign since entering service.

Most of the expenses were gas turbine related. “Clearly, problems associated with this plant are due at least, in part, to an immature design,” the report said, and while possibly more severe than at other units, are “representative of what can occur during the first years of operation, particularly as a newer technology is pushed to expand its limits.”

Overall, excluding nuclear units, average availability of New England generating units dropped 6% from 1995-1998 to 1999-2000, the report said. Last year availability rose to slightly higher levels than in 1995. Besides problems with new combined cycle plants, fossil steam units also played an important role in the overall decline.

The analysis found some were stressed making up for lost nuclear power production and others could have reacted to incentives to keep availability high during peak load seasons, but not necessarily year round. Though annual availability of nonnuclear units declined, the seasonal availability matched demand better in 1999-2000 than it did before, the analysis concluded.

ISO New England Chief Operating Office Stephen G. Whitley said plant owners are responding to economic incentives to keep plants running when demand is highest and are scheduling maintenance during off-peak periods.