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Fluttering Flag Generates Power From Wind

Just by flapping in the wind, a new energy-generating flag produces enough electricity to power small electronic devices. The flag converts mechanical energy into electricity using the effect behind static electricity. Floating high above the ground using balloons, it could harvest high-altitude winds to power weather and environmental monitoring sensors, as well as navigation systems.

Winds at high altitudes are faster and more consistent than those near the ground, but ground-based turbines are unable to reach those heights. Many groups are testing technologies such as floating turbines, kites, sails, and winged craft to harness these high-altitude winds.

“How about a little piece of fabric for wind power?” asks Zhong Lin Wang, a materials science and engineering professor at Georgia Tech, in Atlanta. The flag’s low cost and easy scalability could make it competitive with other airborne wind power technologies, he says.The details of the Georgia Tech team’s research appear in the journal ACS Nano.

The flag operates on the triboelectric effect. When the surfaces of two different materials touch and separate, electrons transfer from one to the other, building up opposite charges on the two surfaces. This can lead to a voltage that drives electric current.

Wang’s group has made several generators that scavenge energy from body movements and mechanical vibrations to produce electricity. In early 2015, the team reported a slinky-shaped generator and an energy-scavenging fabric that could power gadgets using human motion.

The flag is the researchers’ newest form of triboelectric generator. They made it by weaving together 1.5-centimeter-wide, 30-cm-long strips made from two kinds of fabric. The weft is a nickel-coated polyester textile belt and the warp is a polyimide plastic-coated copper film. All the nickel belts are connected using copper tape to form one electrode; all the copper belts are connected together as the other electrode. The flag, which weighs 15 grams, can be bent, folded and twisted. 

“The weave is loose and there is a few hairs’ distance between the two fabric strips,” Wang explains. So as the flag flutters in artificially generated wind, the two fabric units repeatedly touch and separate from each other, generating power.

At a wind speed of 22 meters per second, the flag produces a maximum of about 40 volts and 30 microamperes. Three flags connected in parallel could light up 16 commercial LEDs. As a demonstration, the researchers connected the flag’s output to a button cell battery that powered a humidity and temperature sensor node that transmits data wirelessly to a computer. This whole system was tethered to a meteorological balloon that hovered in an indoor laboratory where the researchers were able to vary temperature and humidity. 

Hydrogen Adds Longevity to Laptops, Phones, and Drones, But Is It Practical?

Back in August, when we wrote about Intelligent Energy’s prototype fuel cell iPhone, we weren’t totally convinced that it was an idea that would catch on. We’re still not totally convinced, but yesterday at the Consumer Electronics Show in Las Vegas, we stopped by Intelligent Energy’s suite to check out the prototype ourselves, along with a fuel cell-powered MacBook and a drone that can fly for up to two hours on a small canister of hydrogen gas.

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Stable Perovskite Cell Boosts Solar Power

By adding cesium to a kind of crystal known as a perovskite, researchers say they can create tandem solar cells that may be much better at converting light to electricity than conventional solar cells while also being far more stable than previous comparable tandem cells.

Photovoltaic cells based on silicon currently make up about 90 percent of the global photovoltaic market. However, the rate at which the power conversion efficiency of silicon photovoltaics has improved has slowed dramatically, growing only from 25 percent to 25.6 percent in the past 15 years.

In order to create more efficient solar cells while making the most of the existing industrial capacity for silicon photovoltaics, researchers would like to create so-called tandem solar cells that combine silicon with other materials. One set of potential partners for silicon in these cells are perovskites, which are inexpensive and easily produced in labs.

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A Renewable Supergrid in Russia

Russia and Central Asia could rely on an economically viable 100 percent renewable energy system—wind and solar—in 2030,  says a report commissioned by the Neo-Carbon Energy Research Project in Finland. (By economical they mean a price per kilowatt-hour slightly higher than € 0.045 but lower than the cost of energy produced by today’s solar plants.) It's highly doubtful that Russia will actually move to such an energy system, according to the report’s authors, but their simulation at least showed that it’s possible.

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Ossia's Cota Wireless Power Tech Promises to Enable the Internet of Everything

Over the past year or so, we've seen enough companies promising to deliver truly wireless power that we're almost, almost starting to believe in it. But there's an awful lot of hype, compounded by the fact that there are a bunch of very different technologies all targeting the same goal: charging everything, everywhere, without plugs or cables or pads. Recently, we've taken a closer look at a few of these technologies, including uBeam's ultrasonic power transmitters and Energous' WattUp pocket-forming antenna arrays.

Yesterday at CES, we were introduced to Ossia, another company that wants to transform how we power our devices using wireless energy. Ossia's solution, called Cota, uses thousands of tiny antennas to deliver substantial amounts of power directly to embedded receiving antennas in devices located up to 10 meters away. Cota emphasizes safety, efficiency, and reliability, and their technology seems pretty incredible.

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Climate Change Could Challenge the Water Needs of Power Plants

Most power plants need water. As water resources are challenged in coming decades due to climate change, the bulk of the world’s power plants could see reduced capacity, because of water limitations or temperature changes according to a new study published today in Nature Climate Change.

The output of more than than 80 percent of thermoelectric plants could be affected after 2040, according to the research. However, the technologies to mitigate any capacity reductions due to change in water availability already exist.

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Nitrogen Can Triple Energy Capacity of Supercapacitors

Nitrogen can triple the energy storage capacity of carbon-based supercapacitors, researchers in China and the United States say, potentially helping make them competitive against some advanced batteries.

Supercapacitors can capture and release energy much more quickly than batteries, but they usually can store less energy. Most supercapacitors in use today use carbon-based electrodes, because their high-surface area stores more charge. "We are able to make carbon a much better supercapacitor," says Fuqiang Huang, a material chemist at the Shanghai Institute of Ceramics.

The scientists began with a framework of porous silica and lined the pores with carbon. They next etched away the silica, leaving porous tubes 4 to 6 nanometers wide, each made of five or less layers of graphene-like carbon.

They then doped the carbon with nitrogen atoms. The nitrogen altered the otherwise inert carbon, helping chemical reactions occur within the supercapacitor without affecting its electric conductivity.

These changes enhanced the capacitor's ability to store energy by roughly threefold without reducing its ability to quickly charge and discharge. "It is as if we have broken the sound barrier," Huang says.

The scientist say that their devices could store 41 watt-hours per kilogram, comparable to lead-acid batteries.

"A bus can run on an 8 watt-hours per kilogram supercapacitor for 5 kilometers, then recharge for 30 seconds at the depot to run on the trip again,” says I-Wei Chen, a materials physicist at the University of Pennsylvania who also worked on the breakthrough. “This works in a small city or an airport, but there is obviously a lot to be desired," he says. "Our battery has five times the energy, so it can run 25 kilometers and still charge at the same speed. We are then talking about serious applications in a serious way in transportation."

The new supercapacitor does not store as much energy as lithium-ion batteries, which achieve 70 to 250 watt-hours per kilogram. However, the researchers say their supercapacitor beats them on power. The nitrogen supercapacitor can crank out 26 kilowatts per kilogram, while lithium-ion batteries are only capable of 0.2 to 1 kilowatts per kilogram.

The scientists are now investigating ways to create these supercapacitors in a scalable, robust, and inexpensive manner, Huang says. They are also experimenting with a variety of electrolytes to further improve the energy and power of these devices.

They detailed their findings this week in in the journal Science.

Metal Powder: the New Zero-Carbon Fuel?

The two solid fuel boosters that burned for two minutes helping the U.S.’s old space shuttle fleet to reach its orbit each contained 80 tons of aluminum powder, which corresponds to 16 percent of the total weight of the solid fuel.  "This idea of burning metals as a fuel sounds pretty far out there, but this is something that has been done in rockets forever," says Jeffrey Bergthorson, an aeronautics engineer at McGill University in Montreal, Canada.  He and colleagues at McGill and at the European Space Agency  published this week in Applied Energy a study outlining how metal powder could serve as a zero-carbon fuel to power transportation and the grid.

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How the Paris Climate Deal Happened and Why It Matters

One month after the terror attacks that traumatized Paris, the city has produced a climate agreement that is being hailed as a massive expression of hope. On Monday the U.K. Guardian dubbed the Paris Agreement, “the world’s greatest diplomatic success.” Distant observers may be tempted to discount such effusive language as hyperbole, yet there are reasons to be optimistic that last weekend’s climate deal finally sets the world on course towards decisive mutual action against global climate change. 

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"Hydricity" Would Couple Solar Thermal and Hydrogen Power

Solar heat could help generate both electricity and hydrogen fuel at the same time in a system that scientists in Switzerland and the United States call "hydricity." Such a system could supply electricity round-the-clock with an overall efficiency better than many photovoltaic cells, researchers add.

There are two ways solar energy is used to generate electricity. Photovoltaic cells directly convert sunlight to electricity, while solar thermal power plants—also known as concentrating solar power systems—focus sunlight with mirrors, heating water and producing high-pressure steam that drives turbines.

Photovoltaic cells only absorb a portion of the solar spectrum, but they can generate electricity from both direct and diffuse sunlight. Solar thermal power plants can use more wavelengths of the solar spectrum, but they can only operate in direct sunlight, limiting them to sun-rich areas. Moreover, the highest conversion efficiencies reported yet for solar thermal power plants are significantly less than those for photovoltaic cells.

Scientists now suggest that coupling solar thermal power plants with hydrogen fuel production facilities could result in "hydricity" systems competitive with photovoltaic designs.

Today’s solar thermal power plants operate at temperatures of up to roughly 625 degrees C. However, the researchers noted that solar thermal power plants are more efficient at higher temperatures. What’s more, when they reach temperatures above 725 degrees C they can split water into it’s constituents, hydrogen and oxygen.

An integrated "hydricity" system would produce both steam for generating electricity and hydrogen for storing energy. And each makes the other more efficient. Set to produce hydrogen alone, its production efficiency approaches 50 percent, the researchers claim. This is because the high-pressure steam the system generates can easily be used to pressurize hydrogen. The substantial amount of power needed to compress hydrogen fuel for later transport and use is often neglected when it comes to calculating hydrogen production efficiency.

Furthermore, this new solar thermal energy design can generate electricity with standalone efficiencies approaching up to an unprecedented 46 percent, researchers say. This is because the high-temperature steam leaving high-pressure turbines can run a succession of lower-pressure turbines, helping make the most of the solar thermal energy the system collects.

Moreover, the hydrogen fuel the system generates can be burned to  generate electricity after nightfall, for round-the-clock power. The researchers say the efficiency of this hydrogen-to-electricity system could reach up to 70 percent, comparable to the highest reported hydrogen fuel cell efficiencies.

Altogether, the researchers say the sun-to-electricity efficiency of hydricity, averaged over a 24-hour cycle, might approach roughly 35 percent, nearly the efficiency attained using the best multijunction photovoltaic cells combined with batteries. In addition, they note that the hydrogen fuel the system produces could find use in transportation, chemical production, and other industries. Finally, unlike batteries, stored hydrogen neither discharges over time nor degrades with repeated use.

The scientists at Purdue University in West Lafayette, Ind., and the Federal Polytechnic School of Lausanne in Switzerland detailed their findings online 14 December in the journal Proceedings of the National Academy of Sciences.

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