Editor’s Note: Last month our Mountain Bureau reported on an interesting new collaborative effort between Xcel Energy and Abengoa Solar, which has its U.S. headquarters based in Lakewood. The goal of the project is to prove that the heat produced by a solar facility can increase the efficiency of a conventional power plant while also lowering carbon dioxide (CO2) emissions. Successful integration of this technology may enable future large-scale applications of this technology into other power plants. Here are additional details:

Expected to begin construction this month, the four thermal megawatt solar installation will use state-of-the-art parabolic trough collectors developed by Abengoa Solar. The project will consist of building an array of parabolic mirrors designed to concentrate heat from the sun, and using that heat to help make the steam that drives the coal plant’s turbines and generators, making electricity. Using  parabolic mirrors this way is not a new application and, in fact, they’ve been in service for decades to generate electricity at stand-alone concentrated-solar power (or solar-thermal) facilities because they are currently the cheapest source of solar power. Pairing the concentrating mirrors with a coal power plant, however, could make this type of solar power even more cost effective because a significant portion of the cost of a solar-thermal plant is the equipment for converting heat into electricity. The Abengoa Solar project will use existing boilers, turbines, generators and other equipment to reduce this cost.

“The thing that’s attractive about this is you only have to buy the solar field portion of the plant, which is 50 to 60 percent of the cost of the plant,” says Hank Price, director of technology at Abengoa Solar. That could effectively make solar-thermal power about 30 to 50 percent cheaper, according to various estimates. That would equate to a range of about six to 12 cents per kilowatt-hour, which is competitive with many conventional sources of electricity. “It’s potentially the most cost-effective way to get significant solar power on the grid,” he says.

Because parabolic troughs don’t generate sufficiently high temperatures, the heat they produce won’t be fed directly into the turbines. Consequently, in the new demonstration project outside Grand Junction, it will be used to preheat water that will be fed into the coal plant’s boilers, where coal is burned to turn the water into steam. Usually, this preheating is done by siphoning off some coal-generated steam. Under the new design, more of that steam can be directed to the turbine to generate electricity. The net effect is that less coal is used to generate a given amount of electricity, and the augmented system reduces carbon dioxide emissions as much as a stand-alone solar-thermal plant with the same size array, but at a much lower cost, says Craig Turchi, a senior engineer in the concentrated-solar power program at the National Renewable Energy Lab in Golden.

Ken May, Director of Abengoa Solar IST, emphasized the high potential of large-scale applications of the industrial solar installation technology: “Proper use of the solar thermal energy produced at these facilities can improve plant efficiency while lowering CO2 emissions. The successful integration of solar and coal technologies will encourage more widespread use throughout the utility sector.”

For its part, Colorado’s largest power supplier thinks that a positive outcome with the solar thermal project could prove beneficial down the road in reducing the carbon footprint of coal plants. Xcel Energy’s David Wilks, President of the company’s Energy Supply, says, “”We continue to move forward in developing ways to help us reduce our impact on the environment.” 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.”

Closer Look: Parabolic Trough Technology for Industrial Solar Installations

Parabolic trough technology can be used for both electricity generation as well as for producing thermal energy for industrial processes. More extensive use of this technology could have a significant positive impact on the environment. Abengoa Solar’s industrial parabolic trough technology installation utilizes collectors that track the sun during the daytime in order to concentrate solar radiation onto a heat-absorbing pipe located at the focal line of the parabola. The heated fluid that circulates through the pipe reaches high temperatures and, by means of a heat exchanger, produces energy that can be used to generate steam, to heat water or air, or to run an absorption machine for an air conditioning system.