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Solar Boost

Hybridizing fossil plants with solar thermal technology.

Fortnightly Magazine - July 2012

to hybrid generation is eSolar, which produces relatively low 75-meter towers that concentrate solar energy from ground reflectors. “Our basic module size for a steam system combined with combined-cycle gas or coal would be approximately 4 MW electric,” says John Van Scoter, eSolar’s CEO. The company also has a U.S. DOE grant to investigate solar thermal storage, ramping up heat levels to that of superheated steam.

In June, General Electric announced an investment and licensing agreement with eSolar, allowing GE to use eSolar technology and software in its integrated renewable combined-cycle plants, which are based on GE’s FlexEfficiency 50 plant design. With a 61 percent fuel efficiency fueled by gas alone, GE says the FlexEfficiency 50 unit can achieve greater than 70 percent efficiency in combination with solar boosters.

The first project to be developed with this technology combination is a 560-MW solar, wind, and gas hybrid for MetCap Energy Investments, in Turkey. The project includes solar tower technology from eSolar, GE wind turbines, and a 510-MW GE combined-cycle plant. The hybrid’s thermal steam flow is directly integrated into the bottoming cycle of the gas plant’s steam condenser.

Source: FPL

“If we can put 10 percent to 15 percent solar into rated power [as in the MetCap project], it can provide a 6-percent to 8-percent fuel efficiency lift, averaged from daylight generating hours. Where we can drive that fraction higher, there’s an incremental lift,” Gradiola says.

With modular designs, new hybrid investments can be phased in for some plant configurations, easing a fuel-type transition at an older plant, for example. “A solar hybrid can extend the life of a coal plant, and when the coal boiler is retired the rest of the mechanical assets on site can be reused for a large solar installation,” Scoter says.

Dispelling Doubts

Such large-scale installations as the GE-eSolar project in Turkey might help dispel doubts among U.S. utilities considering a solar hybrid development. The potential for solar-coal hybrids among U.S. utilities seems particularly strong. “EPRI studied the potential for adding solar steam into coal and natural gas, looking at combined-cycle plants above a minimum size in 16 states along the South, considering location, solar resources, and available land,” Turchi says. “When they tallied the total market potential, the bottom line was several gigawatts.”

The global adoption of hybrid solar is being led now in areas like the Mediterranean, the Middle East, and North Africa, but the U.S. market seems poised to accelerate rapidly. According to market analysis firm SBI Energy, “The global capacity of utility-scale concentrated solar power (CSP) was 2 GW at the close of 2011 with approximately another 2,500 to 3,500 MW becoming operational in 2012. SBI Energy estimates the cost of the installed base of CSP at the end of 2011 at $9.5 billion with power tower technology increasing its market share.”

Analysts further predict that the U.S. CSP market will move at least as fast as the global market. “While some forecasters believe U.S. concentrating solar power capacity alone will reach 6 GW by 2015 … factors suggest an installation rate consistent with the