No sun? No problem: These parabolic mirrors gather heat energy for a 150-megawatt hybrid solar/natural-gas power plant under construction south of Cairo. During the day, solar heat will displace a fraction of the natural gas required to drive the plant's turbines. At night, natural gas alone will assure continued power generation.
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How solar-thermal energy could shrink coal plants' carbon footprint.
Feeding heat from the sun into coal-fired power stations could turn out to be the cheapest way to simultaneously expand the use of solar energy and trim coal plants' oversize carbon footprints.
At least that's what the Electric Power Research Institute (EPRI), a nonprofit organization backed by the electricity industry, is hoping. Last week, the institute launched a nine-month, $640,000 study to pin down the scale of the opportunity and the engineering challenges involved with making these seemingly disparate technologies work together. The study will examine the potential use of solar-thermal technology at a pair of coal-fired power stations, in New Mexico and North Carolina.
Combining solar power with fossil fuels is not a wholly new idea: over half a dozen new and existing natural-gas power stations are being designed or adapted to incorporate solar-thermal technology, which involves capturing heat generated using fields of mirrors and heat-collection tubes.
Retrofitting existing power plants is a low-cost option for solar-thermal projects because the steam turbines that are needed come for free. Such is the case at a giant natural-gas- and oil-fired power plant operated by the utility Florida Power and Light (FPL) in Martin County, FL, where construction of a solar-thermal collector field of 180,000 mirrors covering roughly 500 acres began in December 2008. Steam turbines can comprise 30 percent of the cost of a stand-alone solar-thermal plant.
FPL's solar field will provide up to 75 megawatts of the Martin County plant's 3,705-megawatt capacity by feeding solar-generated steam into the plant's steam turbines. This solar energy is just sufficient to replace the steam currently generated using relatively inefficient "duct" burners that employ extra gas to increase the heat fed into the steam turbines during spikes in power demand.
Purpose-built hybrid solar/natural-gas power plants, such as those being constructed by Flagsol GmbH in Egypt and by Spanish solar-power developer Abengoa in Morocco and Algeria, should boost efficiency even more. Heat from the solar collector fields will be blended with heat from the gas turbines to produce hotter steam. At retrofitted gas plants or stand-alone solar-thermal plants, steam generated directly from solar collectors tops out at 400 °C. At a purpose-built hybrid plant, this heat can generate 500 to 550 °C steam when combined with the heat already used to power the steam generator, meaning more efficient operation.
But the overall efficiency of retrofitted hybrid solar-gas plants is still limited. That's because a gas steam turbine that has been modified to accommodate waste heat plus solar heat will suffer an efficiency penalty from running at partial load whenever the sun goes down. This is part of the reason why none of the solar-gas hybrid plants under construction rely on solar for more than 15 percent of their power.
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A new strategy could reduce coal plant emissions and cut the cost of solar power.
Concentrating Solar Won't Work in NC
I hate to burst bubbles, but because of a couple of embarrassingly simple facts, concentrating solar, or solar thermal, will be nowhere near economical in North Carolina. Or anywhere in the southeast, for that matter. While the southeast is drenched in solar energy, a huge percentage of the solar light in the southeast is diffused by clouds over the course of the year. CSP (concentrating solar power) requires fully clear skies to operate. Thus, the percentage uptime of a CSP plant is a tiny fraction of what a PV plant might produce. Even the slightest amount of high clouds will crater the output of a CSP plant, while a PV plant will keep on cranking. Anyone who bothers to run the numbers on paper with NC weather, let alone try a pilot plant for a year in NC will be gravely disappointed at its output.
New Mexico, on the other hand, has an abundance of completely cloudless days. Perfect for CSP. Along with Nevada, Utah, Arizona, and much of California.
Good luck!
Re: Concentrating Solar Won't Work in NC
Thanks for pointing out that little oversight on our part Freddy-boy. You did a great job of over-stating the obvious. Keep up the good work.
Re: Concentrating Solar Won't Work in NC
Alternative energy is good stuff but we need to put the good stuff in the right places.
I live in Arizona in an area where wind turbines would be a big waste of money. However, give me some photovoltaic or concentrating solar panels and watch me make kilowatts.
But if I lived on the East Coast of the U.S. where massive amounts of offshore wind are available I would be buying and installing wind turbines like crazy.
If I lived in certain other areas of the good old USA I could have my choice of geothermal, wind or solar. The moral of the story is:
Put the right technology in the right places. We can become energy independent if we believe this is important to the future of our country. Here is a good link to show where we have abundant alternative energy resources [pdf format].
Have a great day :-)
http://www.oceanenergy.org/Pickens_Plan_Plus_Jul_21_08_Ver_1-1.pdf
tomgarven@hotmail.com
I look forward to the day when we no longer use coal for power generation. Maybe we can use Coal To Liquid (CTL) with sequestration for transportation but I even doubt that. However, on with the story.
There are two natural gas powered generating station near where I live in AZ but I will discuss only the one located about 20 miles west of Kingman, AZ. For the most part the construction of the plant was supported by the community, local & state governments. There were of course lots of ideas how to spend all the extra tax revenue everyone was going to be receiving from the operating plant. After the plant was built however the price of natural gas spiked and it sits idle most of the time.
Well what can we do; some solar maybe? This plant is located in an area surrounded by hundreds of acres of open desert. This open area could be used to build some type of solar augmentation. Will it happen; probably not. Why not? No one has the additional $10 million to invest to make the plant a financial success. So why is this important? If we are going to use alternative fuels like natural gas for transportation some day [e.g. over-the-road trucking] instead of power generation then its important.
It is really sad to see these two power stations just rusting away in the desert sun.
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bj
50 Comments
Encouraging future Coal Use is not "Cutting" it.
The author's headline, "Cutting Coal Use with Sunshine" is inaccurate. Any tech that allows the Coal Companies to spin their industry as "green" is to be avoided, considering their mountaintop removals, sludge pits, etc. As we all found out once and for all with the TVA debacle in Tennessee, there is no such thing as clean coal. There has to be other uses to which this research can be applied, surely!
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phoenix
172 Comments
Re: Encouraging future Coal Use is not "Cutting" it.
Although the coal-fired energy industry accounts for over 50% of electricity production in the USA, this massive lumbering behemoth has a ravenous insatiable apetite which has been known to consume entire ecosystems in its path. That doen't mean, however, we have to just turn a blind eye to its environmental destruction. So keep turning up the heat on burning this dirty atmospheric pollutant BJ, because if you'd like see it replaced with solar-thermal, solar-voltaic alternatives your not alone.
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Kevin Bullis
177 Comments
Re: Encouraging future Coal Use is not "Cutting" it.
Point taken about the environmental problems with coal.
The pairing of solar and coal, however, doesn't encourage coal use--as long as existing coal plants are retrofitted with solar technology, instead of new coal plants being built. And the retrofits would allow more solar technology to be installed, since money would be saved by using existing steam turbines.
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phoenix
172 Comments
Re: Encouraging future Coal Use is not "Cutting" it.
Although during the Industrial Revolution, England was responsible for supplying about two thirds of the worlds demand for coal, the Royal Navy stopped using it to power their fleet of battleships once they were able to convert them to burning oil instead. That monumental shift in replacing one form of an antiquated technology with a slightly more advanced one, has apparently been lost on the Utlility Cartels, at least up until now. I guess all that smog released by the continued burning of this overly abundant, and reasonably cheap fossil fuel, has affected their thinking, and virtually obscured the light of sustainable energy production at the end of the proverbial tunnel in the process.
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