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Supercritical Carbon Dioxide Can Make Electric Turbines Greener

The U.S. Department of Energy (DOE) is on the hunt for technologies that can support a smarter electric grid. It is currently devoting millions of dollars, via its SunShot Initiative, to create more efficient photovoltaic systems. But in addition to the solar power that is SunShot's focus, the DOE it is looking to improve conventional electric power generation. Sandia National Laboratories in Albuquerque, New Mexico, along with its new partners, has received $8 million to make advances in supercritical carbon dioxide gas turbines.

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Synchronization Controls Could Help Smooth Microgrids

Circadian rhythms and microgrids might not seem to have much in common, but in the world of theoretical mathematics, they do.

New research published Friday in Science Advances suggests that the same mathematical models that help scientists better understand and explain biological phenomena could also be applied to making small, islanded power grids run more efficiently.

Microgrids come in various flavors, but usually they are localized grids that can disconnect from the larger power grid and operate independently. More recently, microgrids have combined clean energy generation and more traditional generation (such as diesel or natural gas turbines) to deliver both heat and electric power. They manage current with energy storage and controls.

Because the grids are small, they’re prone to more severe fluctuations in voltage and frequency than are larger grids, which can more easily smooth fluctuations across their wider systems.

This is where a well known mathematical model for synchronization, the Kuramoto model, can help, says Per Sebastian Skardal, assistant professor of mathematics at Trinity College and lead author of the paper.

The Kuramoto model is a phase oscillator model that defines each oscillator as just a phase angle. The behavior of each phase depends on its interaction with the other phases, explains Skardal.

The model has helped to explain the synchronization of various processes, including the rhythmic flashing of fireflies and neurons firing in the brain. “With the power grid, on the other hand, we are going one step further and using what we know about networks and synchronization to make deliberate choices to improve the functionality of a given system,” says Skardal.

Skardal and his collaborators found that in islanded microgrids that are disconnected from the large power grid, there are essentially a few problematic oscillators. They tend to prefer a frequency that is either much higher or lower than the other oscillators in the network, or they’re loosely coupled to the network. These problematic oscillators could be a set of solar panels that have widely variable output, or a large power draw that turns on and off suddenly.

Skardal says the model should apply regardless of the microgrid configuration. Although the work is firmly theoretical at this point, Skardal and his collaborator Alex Arenas, professor of physics at Rovira i Virgili University in Spain, are interested in applied mathematics, which would take further studies and engineering work.

The model would ultimately inform control systems for microgrids, giving the ability to identify the problem oscillators and adjust them in real time. Preventing or minimizing the grid fluctuations within a microgrid could potentially reduce costs because fewer inverters would be needed or a more simplified and standardized control scheme could be implemented.

Whether this research would apply to a microgrid when it is connected to the main power grid, or help to limit fluctuations in larger power grids whose stability is affected by the variability of inputs from renewable energy sources, is yet to be seen.

Skardal says he believes both may be future applications of the current research, but it is too early to say for sure. In the case of a microgrid that is not islanded, “I believe that the intuition behind the idea will hold,” says Skardal. But the Kuramoto network model would have to be adjusted to take some external forcing, which would be the influence of the larger grid, into account. 

For large power grids with high levels of renewable energy generation, the complexity of the system would make the model more complicated, but the same math could potentially apply.

But power grids aren’t the only things that could benefit from this line of research, the authors argue. “We hypothesize that our findings here may potentially shed some light on the control of synchronization in other contexts,” they conclude in the paper, “such as cardiac physiology and neuroscience.”

New Mapping Tools Show Just How Bad China's Air Pollution Really Is

By crunching data from satellites and ground monitoring stations, environmental scientists are creating maps and forecasts that reveal the scope of China’s air pollution problem in unprecedented detail. The big question is: Will all this data have any impact on environmental policy?  

The maps show that China’s air pollution is beyond bad, it’s catastrophic. In Beijing, residents are responding to the ongoing “airpocalypse” by wearing heavy-duty respirator masks as they go about their daily business, or, increasingly, by never going outside. Fancy schools now feature domes that enclose their playgrounds and sports fields, and residential towers connect directly to underground malls and subway stations. 

At the time of this writing, Beijing’s air quality index is 159, which is actually a pretty good day for the megacity. True, the widely used EPA rating system calls anything above 150 “unhealthy,” likely to aggravate heart and lung conditions and to cause respiratory problems among the general population. But there have been days when Beijing’s air quality is literally off the charts, exceeding the “hazardous” rating that tops out at 500. 

A number of existing websites and apps provide real-time air quality info for worried city residents wondering if they dare cycle to work or open their windows. But precise data for air quality across the country has been hard to come by, and both forecasts and historical data have been lacking. A startup and a nonprofit, both hailing from the San Francisco area, are now addressing those gaps.

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Google Introduces Project Sunroof

Does it make sense to install solar panels on your roof? You probably have no idea. But as of today, Google knows. The colorful and recently alphabetized search monstrosity has launched a new tool called Project Sunroof. It will use data you may not have realized that Google even had to tell you how much money you can save by turning your roof into a photon harvester.

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Hourly Model of Air Pollution Can Reduce Health Costs

Fossil-fuel-burning power plants can reduce the impact their pollution has on air quality and human health by controlling how active they are during certain hours, scientists at Georgia Institute of Technology say. These findings could help limit the drawbacks of generating electricity from fossil fuels without additional investment, they add.

Burning coal and other fossil fuels releases pollutants such as sulfur dioxide and nitrogen oxides. Prior research suggested that air pollution causes 200,000 early deaths each year in the United States alone.

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MIT Has Plans for a Real ARC Fusion Reactor

The Marvel movie version of Tony Stark graduated from MIT in the early 1990s. He built an ARC reactor at Stark Industries later on, but apparently, some of the initial research he did as an undergrad stuck around in some notebooks somewhere on a dusty shelf at MIT. It took them only a few decades, but a team of MIT researchers has been able to develop tentative plans for a fully armed and operational ARC fusion reactor of their own.

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Supercomputer Network Simulates Material That Might Not Melt in a Sunspot

Computer simulations can save time and money when investigating new technical designs but also when looking for new materials. Some serious supercomputing helped two scientists at Brown University in Providence, RI, to—virtually—break a melting-point record.

The current record is held by a mixture of hafnium, tantalum, and carbon (Ta4HfC5), which melts at 4,215 K (3942 oC).  The Brown scientists predicted that a material made up from a mixture of hafnium, nitrogen, and carbon, could have an even higher melting point, 4,400 K (4127 oC), which is about two thirds the temperature at the sun's surface. (Sunspots range from 3000 – 4500 K, so such a material would probably stay solid in one.) At that temperature, the theoretical material would emit light with an intensity about one third of the sun’s surface. The researchers, Axel van de Walle and Qi-Jun Hong, published the results of the computer simulations of this compound in the journal Physical Review B on in June.

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Renewables to Overtake King Coal Under Obama Carbon Regs

At the White House on Monday, President Obama announced final rules intended to cut carbon emissions from the electric power sector by nearly one-third by 2030. The rules, part of Obama's Clean Power Plan, are projected to turn the tables on today’s power supply mix, putting King Coal one rung below renewable power sources. 

The U.S. Environmental Protection Agency (EPA) projects that full compliance with the rules will drive down the portion of the nation’s power supply that comes from burning coal to 27 percent by 2030—a major slip from its 39 percent share in 2013. Renewables will more than double their share of U.S. power generation over the same period, rising from 13 percent to 28 percent, projects the EPA.

Natural gas–fired generation is expected to maintain its current role of roughly 27 percent, rather than grow substatially as predicted when EPA released its draft plan in June 2014.

Timelines for initial compliance, meanwhile, have slipped back two years to 2022. This is mainly the result of the power industry’s complaint that a compliance regime beginning in 2020 would spur a rushed shuttering of coal-fired power plants and increase the risk of power grid blackouts

Despite the delay, however, the final rule is actually projected to achieve greater carbon reductions. By 2030, the EPA projects, carbon emissions from the power sector will be 32 percent lower than their 2005 level, an improvement on the 30 percent goal in the EPA’s 2014 proposal. This reflects, to a large extent, the carry-forward effect of strong recent growth in installations of renewable generation such as solar panels.

Obama said the pledged action by the United States sets the stage for an international deal at the Paris climate change negotiations to take place later this year. “In December, with America leading the way, we have the chance to put together one of the most ambitious international climate agreements in history,” said Obama.

The North American Electric Reliability Corporation (NERC), which sets grid standards, issued a statement yesterday saying it was pleased that “the final rule addresses several topics identified as needing attention” in its evaluations of EPA’s proposal. “NERC’s principal finding recommended additional time in order to allow for extensive planning and significant investments in new energy infrastructure that will be needed to achieve emission reduction goals,” said NERC in its statement. 

The Washington, D.C.-based Edison Electric Institute, a trade group representing investor-owned utilities, struck an equally conciliatory tone. In a statement issued yesterday, EEI president Tom Kuhn welcomed the flexibility offered by the final rules and said they would “work with the states” as they develop plans to comply with the rules. “Today utilities are focused on the transition to a cleaner generating fleet,” said Kuhn.

Many leaders in the Republican party continue to express serious doubts as to the existence of climate change, or of its human origins, and adjusting the deadlines did not shake their opposition to Obama’s Clean Power Plan. However, Obama’s plan may pencil out even without its climate benefits. EPA Administrator Gina McCarthy has estimated that, thanks largely to the health benefits from reduced smog and soot emissions under the plan, its economic benefit will be 4 to 7 times larger than the $8.4 billion in costs that the EPA is projecting through 2030. 

At yesterday’s White House ceremony, Obama recalled an early personal experience with air pollution, and drew a lesson about critics of air pollution controls. Obama said his lungs constricted when he went running on his first day in Los Angeles in 1979, fresh off an airplane from Hawaii to attend Occidental College. “After about 5 minutes I had this weird feeling like I couldn’t breathe,” recalled the President. 

Obama predicted that, just as ingenuity triumphed over pessimism to clean up LA’s air, innovation and determination could deliver a lower-carbon power system in the years ahead without bankrupting the U.S. or global economies. “Because we pushed through despite those scaremongering tactics, you can actually run in LA without choking. We’ve got to learn lessons and know our history. We can figure this stuff out. We can upend old ways of thinking,” said Obama.

One such innovation is highlighted in the pages of this month’s issue of Spectrum: repurposing old power plant generators to function as voltage stabilizers, thus facilitating the importation of power from more distant power plants or intermittent renewable energy sources. Turning aging coal, gas and nuclear plants into synchronous condensers is a new spin on a rather old idea -- one that’s likely to have even more relevance thanks to the Clean Power Plan. 

Images by Zhiyuan Huang/UC Riverside

Solar Cells Could Capture Infrared Rays for More Power

Solar cell efficiencies could increase by 30 percent or more with new hybrid materials that make use of the infrared portion of the solar spectrum, researchers say.

Visible light accounts for under half of the solar energy that reaches Earth's surface. Nearly all of the rest comes from infrared radiation. However, solar infrared rays normally passes right through the photovoltaic materials that make up today's solar cells.

Now scientists at the University of California, Riverside, have created hybrid materials that can make use of solar infrared rays. The energy from every two infrared rays they capture is combined or “upconverted” into a higher-energy photon that is readily absorbed by photovoltaic cells, generating electricity from light that would normally be wasted.

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Boosting the Transfer Efficiency of Wireless Power Transfer Systems

The wireless transfer of electric current that charges your electric toothbrush is highly efficient: The receiver coil in the handle of the toothbrush fits tightly around the transmitter coil in the charger, making the process about as lossless the operation of the ubiquitous transformer. 

However, using wireless power transfer for electric cars by charging them with transmitter coils embedded in the pavement is more problematic.  The receiver coil in the car has to be placed as close as possible to the ground; still, only a part of the transmitted energy reaches the receiver coil. 

Now researchers from North Carolina State University and Carnegie Mellon University say they have hit upon a way to boost the efficiency of the energy transfer in that situation. They reported, in a paper published in the online edition of the journal IEEE Antennas and Wireless Propagation Letters, that by placing a magnetic resonance field enhancer (MRFE)—a loop of copper wire resonating at the same frequency as the AC current feeding the transmitter coil—between the transmitter and receiver coil, they could boost the transmission efficiency by at least 100 percent. “Our experimental results show double the efficiency using the MRFE in comparison to air alone,” David Ricketts of NC State, said in a press release. The MRFE increases the strength of the magnetic field that reaches the receiver coil, resulting in an increase of the transmission efficiency.

Previously, the team had investigated the use of metamaterials to enhance the magnetic field. “We performed a comprehensive analysis using computer models of wireless power systems and found that MRFE could ultimately be five times as efficient as using metamaterials and offer 50 times the efficiency of transmitting through air alone,” Ricketts says.  

For their experimental setup, the team used two coils of 4.25-centimeter- diameter copper wire with six turns for the transmitter and receiver coils.  The coils were separated by 12.2 cm and the transmitter coil was powered with a 2.94-megahertz signal. They measured the transmission efficiency by placing a metamaterial between the transmitter and receiver coil and comparing it with a setup where a single, 12-cm-diameter copper-wire loop replaced the metamaterial. They found that the copper wire version improved the efficiency by a factor of almost two.

These laboratory experiments, though much smaller systems than would be used in the future applications the researchers envision, clearly indicate how transmission efficiency could be tweaked. “This [research] could help advance efforts to develop wireless power transfer technologies for use with electric vehicles, in buildings, or in any other application where enhanced efficiency or greater distances are important considerations,” Ricketts says.


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