By Brian Wheeler, Associate Editor
In September 2010, the Martin Next Generation Solar Energy Center generated its first solar-powered steam and has been providing heat to reduce a nearby combined cycle power plant’s fossil fuel consumption ever since. The Florida Power and Light-owned and operated solar thermal power plant is among the world’s first hybrid solar plants to connect to an existing power plant.
Aerial view of the natural gas plant (right background) and the more than 190,000 mirrors (foreground) used at the Martin Solar Energy Center. Photo courtesy FPL.
Construction began in 2009. With 1,000 workers on-site, the 75 MW solar plant was completed for $400 million, about $75 million under budget. The solar field is on 500 acres of the 11,000-acre site, which includes the 3,600 MW Martin combined cycle power plant. Located near Indiantown, Fla., the solar plant is made up of more than 190,000 parabolic mirrors that concentrate the sun’s thermal energy onto 53 linear miles of heat collection elements that contain heat transfer fluid known as Dowtherm A. The fluid heats up to nearly 740 F and is pumped through heat exchangers to produce steam from feed water supplied by the existing plant. The steam is then sent to existing Nooter-Erikson combined-cycle heat recovery steam generators (HRSG’s) and is further superheated to final steam turbine inlet conditions.
The solar field has been integrated with a pre-existing 1,150 MW combined-cycle natural gas fired plant at the Martin site equipped with four GE 7FA combustion turbines. Gary Kowalczyk, plant manager for both the Martin solar and fossil facilities, said the HRSG’s at the 4×1 combined-cycle plant are equipped with duct burners that can generate 100 additional megawatts of steam to a Toshiba steam turbine. Solar thermal is now displacing the need to fire the less efficient natural gas-fired duct burners.
“The steam (produced by the solar field) offsets the natural gas afterburners so it is also a fuel savings for the customer and very efficient,” he said.
When the solar field is operating at full capacity, the plant achieves a 500 Btu/kWh heat rate reduction, which Kowalczyk called a “positive environmental aspect.”
One concern for FPL when tying-in to the existing fossil plant was to maintain HRSG drum level control without upsetting generation on the existing unit. Once the solar plant began generating steam, plant engineers tuning the system found the control challenge very manageable.
“There were some valve issues initially, but the startup process of supplying solar generated steam to the units for the first time went remarkably well,” said Bruce Kullman, lead plant engineer.
Kullman said the project team responsible for getting the plant commercially operational benefited from the experience from other solar power plants the company owns and operates. NextEra Energy Services, of which FPL is a subsidy, operates one of the largest solar power facilities in the world. The Solar Electric Generating Systems (SEGS) plant in California’s Mojave Desert is made up of nine solar plants that generate roughly 354 MW. And there are two other solar photovoltaic sites in Florida that are also operational.
“Solar generation is not new to us, but this is the first-of-its-kind tied-in to an existing plant,” said Kowalczyk.
Even with the challenge of harnessing the sun’s energy through cloud cover and rainy days, Kowalczyk said the plant has achieved full capacity on numerous occasions. He said the hybrid solar concept can be used at other existing fossil units.
Over its lifetime, the Martin Next Generation Solar Energy Center is expected to save FPL customers an estimated $178 million in fuel costs and prevent the release of 2.75 million tons of greenhouse gases. It will do that by reducing fossil-fuel usage by some 41 billion cubic feet of natural gas and 600,000 barrels of oil. The 75 MW facility is also the United States’ largest solar thermal plant outside of California and is expected to generate about 155,000 MWh annually.
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