Solar

The first utility-scale solar hybrid in the United States was the 75-MW solar baseload addition to Florida Power & Light’s 3,705-MW Martin combined-cycle generating facility near Indiantown, Fla. The lead contractor was Rioglass America LLC. The solar unit, completed in 2010, includes 190,000 reflecting mirrors spread over 500 acres to concentrate light with basic parabolic, or trough concentrating technology, which is the most common type of concentrating solar installed in the United States.

The $398 million hybrid addition was approved in advance under a 2008 state law approving the construction of 110 MW of renewable energy in the state, according to Buck Martinez, a senior director of development at the utility. FPL covered the costs with balance-sheet funding, buoyed by an $850 million 30-year bond issue last year.

The Martin solar system has been ramping up production levels steadily. “Last month we hit 85 MW nominal, our highest production to date, and our goal is to get to 155,000 MWh in the near future,” says Martinez.

The plant hasn’t been without its startup problems; last year, a burst valve resulted in the loss of 46,000 gallons of heat transfer fluid, requiring the removal of some 1,000 truckloads of affected soil.–CWT

Xcel Energy in 2010 successfully tested a 2-MW, $4.5 million solar hybrid solution from Abengoa Solar, to boost efficiency by about 5 percent at its Cameo coal-fired plant near Grand Junction, Colo. The Cameo hybrid addition was approved in 2009 by the Colorado Public Utilities Commission, under an Innovative Clean Technology program.

The first of its kind in the United States, the hybrid test was designed largely to help reduce emissions, according to Xcel spokesman Gabriel Romero. Overall, more than 500,000 pounds of coal were saved during the year-long test, and 2,000 tons of carbon dioxide emissions were avoided.

The measured goal of the installation was simple. “If solar provides 20 percent of the fuel for steam production, then you reduce coal consumption by 20 percent and you reduce dioxide emissions by 20 percent,” says Bruce Kelly, a technical specialist at Abengoa.

Temperatures of the food-grade oil heating fluid, heated in the 6.4 acre parabolic solar array, reached 576 degrees F. The heated fluid was used to preheat the feed water in the coal boiler, eliminating the need to divert heat from the steam turbine. “During daylight operation, solar replaces coal for much of the energy supply,” Kelly says. “As the radiation decreases during the late afternoon hours, the coal contribution replaces the solar contribution, allowing the boiler to operate at full load at all times. In the early morning hours, the process is done in reverse, gradually replacing the coal energy contribution to solar, while maintaining the technical minimum to optimize the operation of the coal boiler.”

While the Cameo test equipment has since been dismantled for use in a solar storage project elsewhere, the utility is considering other solar hybrids. At the time of the hybrid announcement, David Wilks, president of energy supply for Xcel Energy, said, “If this demonstration works, we may be able to implement this type of technological advance in other coal-fired power plants to help further reduce carbon dioxide emissions in Colorado and possibly other areas of our service territory.”

Toward that end, the vendor is currently promoting the technology. “Abengoa is now pursuing the concept where you put in solar-heated steam at the same conditions as the existing coal-heated steam plant already operates,” says Kelly.–CWT