By Jim Loney

MIAMI, June 25 (Reuters) - FPL Group Inc (FPL.N: Quote, Profile, Research) unveiled plans on Wednesday to build 110 megawatts of solar-power generating plants in Florida as part of a long-term goal to ramp up its renewable energy portfolio, the company's chief executive said.

The new plants would take FPL more than a third of the way to a goal announced last year to build a total of 300-MW of solar capacity in Florida, and the company is more bullish than ever on the prospects for solar, Chief Executive Lew Hay told Reuters in an interview.

Florida Power & Light, an FPL subsidiary, said it would build a 75-MW solar-thermal plant at an existing FPL site in Florida's Martin County, and two photovoltaic plants, one of 25 MW in DeSoto County and one of 10 MW at the Kennedy Space Center on the east coast.

The projects, which have not yet been approved by state regulators, carry a $688 million price tag and would provide power enough for 35,000 customers, the utility said.

"Costs are coming down and they're coming down more rapidly than I would have thought," Hay said.

Coupled with the skyrocketing cost of conventional power-plant fuels like oil and natural gas and the rising price of commodities to build such power plants, solar is becoming more competitive, Hay said.

The company, which bills itself as the top U.S. producer of wind power, has other solar projects on the drawing board, he said.

"We've been, both in Florida and the southwestern parts of the United States, locking up land, usually through option agreements and in some cases buying it outright, for future projects," he said.