Benefits of shopping for power.

Brokers and suppliers say the offers that commercial and industrial customers receive depend upon many factors: the customer's energy-use profile, its credit rating, and its appetite for price risk.

More risk-tolerant customers might opt for market rates, which can vary hourly depending on season, weather, and demand. Suppliers also may offer incentives to customers that can curtail their demand during peak periods, when costs are high.

The Hill School, for instance, can shift much of its electrical load to off-peak evening hours because it makes tons of ice at night that is used during the day to cool many of the campus' 50 buildings. The novel air-conditioning system is built around ice-making equipment originally installed in 1952 for the school's hockey rink.

"Making ice in off-hours makes us an attractive customer, because our peak demand in the summer is not that high," Silverson said.

The 500-student prep school also maintains a 125-kilowatt diesel generator that can supply about 20 percent of its electrical power when the utility asks it to shed its load during peak hours - also meriting a discount rate.

Some customers are investing in conservation measures to reduce costs, said Thomas Petrella, regional sales manager for Hess Energy Marketing.

"For many customers, energy is one of their top three costs," he said. "Some are looking at moving shifts around to take advantage of discounted power."

Advocates of competition say the new market-based system will lead to innovations similar to the transformation of telecommunications after the phone system was restructured in the 1980s.

"If the goal is to change people's consumption so they use electricity more efficiently and cost-effectively so we don't have to build big new power plants, that's a win for the environment, and that's a win for customers," said David I. Fein, a vice president for energy policy for Constellation Energy Group.

"Those are the type of market signals that people need."

Power Shopping

Pennsylvania's Public Utility Commission explains electrical choices and lists alternative suppliers at www.papowerswitch.com.

Peco Energy Co. responds to customer questions at www.pecoanswers.com.

Contact staff writer Andrew Maykuth at 215-854-2947 or amaykuth@phillynews.com.