Utilities across the nation are on the hot seat this summer, sweating over generating enough power to keep customers cool while keeping factories running.

What seemed like a simple premise - matching supply with demand - has become fraught with problems. Utilities are plagued by aging plants and power-transmission networks at a time when Americans' love of gadgets is putting more of a strain on the system.There already was one scare during a heat wave last month, when utilities saw their electric reserves depleted and storms knocked out some service. Now, at least one major power provider now is proposing paying big business to turn off electricity in the next crunch.

Utilities were forced during a late June heat wave in the East and Midwest to beg and borrow electricity. Many also had to dust off "rolling" blackout plans to avoid unthinkable cascading outages as reserves dwindled to nothing.

"Frankly, we're still trying to figure out exactly what's happening," said James Owen, spokesman for Edison Electric Institute, a trade association for public utilities. "Utilities recently had to scramble to come up with power to meet customers' needs, but it's important to remember that the system did work, there were no major blackouts."

Electricity that was selling in the range of $30 per megawatt hour soared as high as $7,500 in late June when a powerful storm that downed transmission lines and unexpected plant shutdowns caused some power marketers to default on contracts.

Chicago-based ComEd this week promoted the unusual idea of paying big businesses in northern Illinois the going rate for electricity to turn off all power at a moment's notice.

Utilities for decades have relied on a system in which they generate power from nuclear-powered or coal-fired plants. They buy power from each other when demand is heavy. It then is routed through a series of transmission grids across the nation.

But over the past decade, as Americans increasingly use more high-powered devices at home and at work, nary a new power generation plant has been built, and the aging transmission grids can shuttle only so much power before burning out.

And nuclear power plants have not lived up to their reputation, with many operating below optimal performance levels, shut down unexpectedly or for maintenance.

Critics, meantime, contend utilities are placing an unacceptable risk on business and residential customers.

"They're gambling on the ability to wheel in more power," David Stahr, research director of Illinois watchdog group Consumer Action, said Friday. "They're gambling on the weather (being cooler than normal) to reliably keep lights on."