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Published on May 29th, 2017 | by Tina Casey


Energy Dept. Is Super Excited Over Supercritical Carbon Dioxide Turbine

May 29th, 2017 by  

There they go again. last Friday, just as US President and enthusiastic fossil energy fan Donald J. Trump was in the thick of rendering a key decision on US energy policy, his own Department of Energy weighed in with some great news about renewable energy. For good measure, this time around DOE also took the opportunity to push back against the President’s proposed budget, which would take the axe to its Office of Energy Efficiency and Renewable Energy.

solar CSP GE turbine carbon dioxide

The Paris Climate Agreement: No News Is Good News…So Far

Before we get to that good news about renewables, let’s check in on that key decision forthcoming from President Trump.

The President has just returned from his first overseas trip, capped by a meeting of the G7 group of industrialized nations. The group was expected to renew its pledge to the Paris climate accord, but in true reality show fashion the President left everyone in suspense.

The G7 meeting concluded without a climate change pledge from the US (for the record, everyone failed to render a pledge of fossil fuel subsidies but whatever).

On Saturday the President deployed Twitter to raise the tension another notch:

I will make my final decision on the Paris Accord next week!

So, there’s that.

More Good News About Renewable Energy

Meanwhile, despite Trump’s pro-coal rhetoric, Energy Secretary Rick Perry has kept the DOE media machine turned up to 11 on a scale of 10 when it comes to promoting the agency’s programs for wind and solar.

In effect, Perry has been making a “stealth” case for renewables — and for DOE scientists and engineers — that makes it more difficult, though not impossible, for Trump and the Republican-lead Congress to enact massive budget cuts.

This latest example is a case in point. Last Friday DOE pumped out a new article under the auspices of its SunShot solar program. The article hypes an a “game changing” turbine for power plants that could be up to 30% more efficient than conventional turbines.

The thing is, the turbine itself is not exactly fresh news.

The new turbine is well into the R&D stage through GE and its partners under the SunShot umbrella. Back in 2015 DOE even got a nice writeup about the program in Scientific American.

Last year the Obama Administration also assigned $80 million to build a 10-megawatt test facility to smooth the path to commercialization of the new turbine.

What makes the turbine newsworthy is the latest issue of the journal Science, which showcases SunShot research for deploying the new turbine in concentrating solar power plants.

In its article, SunShot makes it clear that the news hook is more on the Science placement that on the technology itself.

Here’s the title of SunShot’s article:

SunShot CSP Research Showcased in Science Magazine

And, here’s the lede:

Science magazine, an internationally renowned journal for scientific research, features SunShot Initiative concentrating solar power (CSP) research in its late spring edition.


The new turbine really is expected to be a game-changer for concentrating solar power (we’ll get to that in a minute), but DOE seems even more excited about the implications for holding on to its staff in the face of looming budget cuts. SunShot caps off its article with this observation:

Science magazine has more than 125,000 subscribers across the country and is the largest paid circulation, peer-reviewed general science journal. A staple in most doctor’s offices and research laboratories, the magazine is highly regarded and an article published in this prestigious journal demonstrates the technical expertise of SunShot’s staff.

So. There.

About That New Turbine

As for the new turbine, that would be the supercritical carbon dioxide turbine developed by GE Global Research in partnership with the Southwestern Research Institute.

The idea is that using extra hot, extra pressurized CO2 instead of steam will ramp up efficiency (in those conditions, CO2 acts like a dense liquid). The trick is to design a turbine that can withstand temperatures topping 700 degrees Celsius, with pressure inching up to the 3,600 psi range.

GE scientist Doug Hofer is leading the R&D team. Here’s his rundown:

“The pressure and fluid density at the exit of our turbine is two orders of magnitude higher than in a steam turbine…Therefore, to push the same mass through, you can have a much smaller turbine because the flow at the exit end is much denser.”

The result is a 10 megawatt turbine that can fit on a tabletop but pump out enough juice for 10,000 typical U.S. homes.

No, really.

Btw, those of you eyeballing the new turbine for carbon capture can forget about it. The system is a closed loop and only requires a “small amount” of carbon dioxide.

What About Concentrating Solar Power?

The new turbine could be deployed in any steam power plant, and energy stakeholders seem particularly excited about the implications for improving the efficiency of gas fired power plants. For that matter, DOE’s Fossil Energy office is also involved in the test facility.

SunShot comes in because of the concentrating solar angle. Here’s the agency’s rundown on the test facility:

The proposed s-CO2 system uses no water, which is significant given that CSP plants are typically located in hot, dry climates where water is scarce. Researchers plan to demonstrate the inherent efficiencies of the s-CO2 power turbine and associated turbomachinery at a scale relevant to commercial CSP projects.

SunShot sets the expectations pretty high:

Success in this endeavor will provide a foundation for solar applications that exceed the SunShot Initiative’s goal of 50% net thermal-to-electric conversion efficiency.

That’s nice, but if you’re wondering how heat from a CSP facility would make it over to the carbon dioxide, so is everybody else.

The kinks are still being worked out but DOE’s Sandia National Laboratory is on to a possible solution. The lab has been working with private sector partners to explore supercritical CO2 for solar applications as well as fossil power plants.

Sandia runs the nation’s only solar thermal test facility, and in 2015 it began testing a heat transfer method that involves dropping tiny ceramic particles through the concentrated solar beam of a CSP.

No, Really, What About CSP?

If the Sandia research pans out, the supercritical carbon dioxide turbine could amp up the concentrating solar power field.

Over the years, the CSP industry in the US has had its ups and downs, mainly because CSP facilities tend to be more expensive than conventional solar arrays. However, DOE has continued to hold a torch for CSP. The technology’s affinity with solar energy storage gives it 24/7 capabilities, an important advantage over conventional solar arrays.

Right now CSPs typically rely on molten salt for heat transfer and energy storage.

Here’s Sandia on the potential impact of substituting ceramic “sand” for molten salt:

The technology can capture and store heat at high temperatures without breaking down, unlike conventional molten-salt systems. Higher temperatures mean more available energy and cheaper storage costs because less material is needed to transfer heat.

Now combine that with the efficiency gain from a supercritical CO2 turbine and you’re cooking with gas, so to speak.

The DOE cutting-edge tech funding office ARPA-E is also supporting the new turbine.

ARPA-E is interested in the efficiency potentials for a hybrid system that combines CSP and the new turbine with a conventional solar array. To that end ARPA-E awarded a cool $2 million to GE for R&D, with this observation:

Combining the best elements of these two technologies could provide a means to get the most out of the full solar spectrum, generating both electricity and storable heat (for later use) within the same system. Developing hybrid solar energy systems that perform both functions at the same time could provide electricity at cost comparable to traditional sources, whether the sun is shining or not.

Game on!

Photo (screenshot, flipped): Supercritical carbon dioxide turbine via GE.

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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

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