Alliant Energy Corp. in Madison will have an 18 percent reserve margin. "Given reasonable performance from the major generating plants in the state, given a normal hot summer .

If the economy picks up, that could also increase demand, which was blunted slightly last summer. "The fact of the matter is, utilities never really know what their peak load potential is until it happens," said Roy Thilly, chief executive officer of Wisconsin Public Power, a Sun Prairie power company owned by 37 municipal electric utilities. "So you can be surprised."

Another thing to watch is how other Midwestern states' power systems hold up.

"The thing that has changed all over the country is that markets are much more regional," said PSC commissioner Ave Bie. "If there is an issue in another state, it could impact Wisconsin."

Supplies are not the only big variable this summer. "The question consumers have asked us over the past year is not whether the lights will stay on but at what price," PSC commissioner Robert Garvin said.

Natural gas demand is up 9 percent over last year nationwide, Garvin said, and few new resources are available. Meanwhile, most new power plants being built around the country are fueled by natural gas. The result was gas price spikes this winter, Garvin said, a problem that could continue.

Wisconsin will have one new power plant operating this year, the 83-megawatt Pulliam plant for Wisconsin Public Service Corp. of Green Bay. At the same time, one unit of We Energies of Milwaukee's Port Washington coal plant has been decommissioned, dropping 97 megawatts. The plant will be converted to natural gas fuel by 2005.

Next year, independent power producer Calpine should have the Riverside plant in Beloit on line, with 600 megawatts. Much of that is under contract to WPL and MGE.

But four other independent producers' plants that had been approved by the PSC will not be built and an application for a fifth plant has been withdrawn. Together, they would have added 3,125 megawatts of capacity within the state.