The company did not provide estimates of rate changes when additional plants are due to go on line in 2014 and 2016.
FPL is the state's largest electric utility, serving about 4.6 million homes, businesses and other customers in South Florida and along the state's east coast.
The Florida Industrial Power Users Group, South Florida Hospital and Health Care Association and Federal Executive Agencies have agreed to the proposal.
Kelly said they represent an extremely small percentage of FPL's customers. He also noted the Florida Retail Federation, which represents the largest segment of commercial customers, also isn't a party to the deal.
Another aspect of the agreement is a cost shift from high end users to residential and small business customers, Kelly said. He added that while his office represents all consumers, it also has an interest in fairness.
Company figures show that while residential bills will go up, rates for most commercial customers are expected to remain flat or down 3 percent in January. Most small business customers should see a decrease, FPL officials said.
Jon Moyle, a lawyer for the industrial power group, defended the deal.
"This agreement will provide Florida's largest industrial and commercial customers with predictable rates for the next four years, something that is important as the Florida economy emerges from the Great Recession," Moyle said in a statement.
Two years ago, the five-member commission sharply cut rate increases sought by FPL and Progress Energy Florida. Within months of that decision, the Florida Senate refused to confirm two of the commissioners and a nominating panel, which is appointed by legislative leaders, declined to interview two others for reappointment.
The ousted commissioners and then-Gov. Charlie Crist said it was retaliation for rejecting most of the rate increases, which Crist opposed. Opponents argued they were not qualified and complained the commission lacked diversity because it then had no black or Hispanic members.