Three top U.S. power companies posted higher-than-expected quarterly earnings on Wednesday, but drew a mixed picture of the nation's economic outlook and demand for electricity

Exelon Corp , which operates the largest U.S. fleet of nuclear power plants, raised its full-year profit forecast based on results in the first half, when it relied on strong residential and small-business demand to offset weak electricity usage from industrial customers.

NextEra Energy , the largest U.S. renewable energy producer, said its earnings benefited from greater demand at its Florida Power & Light utility and stronger output from its wind farms, but warned of uncertainty ahead.

The economic recovery in Florida appears to continue to take hold, but the progress is slow and uneven, Chief Financial Officer Armando Pimentel Jr. told a conference call.

Still, Southern Co , which is trying to build the first new U.S. nuclear power reactor in decades, said demand had increased in its markets.

The industrial sector continues to lead the economic recovery in the Southeast, Chief Executive Officer Thomas Fanning said in a release. Our region is well positioned for future expansion, and we are already seeing new business development in several parts of our service territory.

The company said second-quarter results also benefited from rising residential demand for power.


Southern's second-quarter profit increased 18 percent to $603.3 million, while revenue rose 7 percent to $4.52 billion.

Exelon's quarterly profit rose 39 percent to $620 million. The company, which is seeking regulatory approvals to buy Constellation Energy Group , raised its full-year forecast to between $4.05 and $4.25 per share from a prior range of $3.90 to $4.20.

Exelon forecast no growth in 2011 overall power demand from customers of its PECO utility in Pennsylvania and Commonwealth Edison customers in Illinois, largely because of moribund demand from its largest users.

NextEra's profit jumped 39 percent to $580 million, even though extended refueling outages at its Seabrook and Point Beach nuclear power plants cut into its earnings. Its shares fell 1.2 percent.

Shares of Exelon were up 0.8 percent, while Southern slipped 0.3 percent.

(Writing by Matt Daily; Editing by Lisa Von Ahn and Gunna Dickson)