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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.

Digging for Geothermal Energy with Hypersonic Projectiles

Geothermal energy might be the most appealing of all renewables. Unlike wind, solar, or even wave or tidal energy, it produces constant and reliable long-term power. Iceland has got this all figured out, but they have it easy. The entire country is (luckily) perched on top of an active volcano. For the rest of us, tapping into geothermal power is harder, because you have to dig for it: About 5 kilometers down, you can find rock hot enough to turn water into steam.

The average depth of an oil well is only about a kilometer and a half, and drilling down to 5 km (especially through hard rock) using conventional technology isn’t trivial and definitely not worth the cost. A company called HyperSciences thinks it has a better way. It wants to harness geothermal energy with a new kind of drilling technology that does away with the “drill” bit completely, using projectiles fired into the ground instead.

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Porous Silicon Battery Electrodes from Reeds

Natural structures in reed leaves could find use in advanced lithium-ion batteries, which could lead to a more sustainable way to create sophisticated energy-storage devices, scientists in China and Germany say.

Silicon-based materials can theoretically store more than 10 times charge than the carbon-based materials most commonly used in the anodes of commercial lithium-ion batteries, making them promising next-generation anode materials. However, silicon’s big problem is that it can swell by more than 300 percent when filled with lithium. The constant swelling and shrinking as the battery charges and discharges, causes the anode to crack. One way to overcome this problem is to make silicon porous enough to accommodate the expansion. But synthesizing these structures is commonly a complex, energy-intensive, and costly process.

Now scientists have developed 3-D porous silicon-based anode materials using the kind of reed leaves that are abundant in temperate wetlands. Reeds naturally absorb silica from the soil, which accumulates in sheet-like structures around micro-compartments in the plants.

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Nanowires Boost Hydrogen Production from Sunlight Tenfold

Using the energy of the sun to split water into hydrogen and oxygen gives you access to a completely carbon-free energy source for transportation. But so far, the efficiency of the process has been a bit disappointing, even when using systems called solar-fuel cells—a solar cells immersed in the water it’s splitting.

Now researchers from Eindhoven University of Technology in The Netherlands and the Dutch Foundation for  Fundamental Research on Matter (FOM) report in the 17 July issue of Nature Communications  that they have improved tenfold the hydrogen producing capacity of a solar fuel cell. The key was to use a photocathode—the electrode that supplies electrons when illuminated by sunlight—made from an array of gallium phosphide nanowires.

Previously, researchers used flat surfaces of the semiconductor gallium phosphide as the photocathode, but light absorption was low.  The GaP nanowires, about 500 nm long and 90 nm thick, increased enormously the surface of the photocathode exposed to light.  By adding platinum particles, its catalytic properties improved hydrogen production even more, report the researchers.

At the same time, the nanowires allowed a drastic reduction in the use of GaP material. “For the nanowires we needed ten thousand times less precious GaP material than in cells with a flat surface. That makes these kinds of cells potentially a great deal cheaper,” said Erik Bakkers of Eindhoven University of Technology, as quoted in a press release.

“In addition, GaP is also able to extract oxygen from the water—so you then actually have a fuel cell in which you can temporarily store your solar energy. In short, for a solar fuels future we cannot ignore gallium phosphide any longer,” he added.

Diesel-Powered Fuel Cell Produces Clean Electricity

Although several options to store hydrogen as a fuel for cars have been investigated, a practical and affordable way to store and distribute hydrogen is still the biggest hurdle to the wide deployment of green, CO2-emission-free cars. Now researchers in Europe have built a demonstration system that might be a first step in circumventing the limitations on hydrogen distribution and storage; they simply extract hydrogen from diesel fuel on the go.  

The research group, "Fuel Cell Based Power Generation (FCGEN)," which includes researchers from Volvo Technology (Sweden), Johnson-Matthey (United Kingdom), Modelon AB (Sweden), PowerCell AB (Sweden), Jožef Stefan Institute (Ljubljana, Slovenia), Forschungszentrum Jülich (Germany) and Fraunhofer ICT-IMM (Mainz, Germany) announced in a recent press release the creation of a prototype 3-kilowatt, diesel-fueled fuel cell system that has operated flawlessly for 10,000 hours. 

The extraction of the hydrogen from the diesel fuel happens through autothermal reforming, a catalytic reaction in which the diesel fuel is decomposed into hydrogen, steam, carbon dioxide, and carbon monoxide.  The CO is then converted to CO2 and water, explains Boštjan Pregelj of the Jožef Stefan Institute, and who is the Principal Investigator of the FCGEN project.

It didn’t escape their notice that the extraction of hydrogen from the diesel fuel releases CO2 directly into the atmosphere.  “Actually all carbon in the diesel is converted to CO2, but since the efficiency [of the overall process] is about five times [that of a diesel] engine idling, fuel consumption is 80 percent lower, and consequently, the produced amount of CO2 is decreased by 80 percent,” says Pregelj. That is why the “green” label was given."

The researchers say that the system could generate between 3 and 10 kW of power in trucks; on small aircraft, it would power air conditioners and refrigeration systems. In addition to lowering CO2 emission, the units produce little noise, making them suitable as mobile electricity generators in places, like field hospitals, where quiet is appreciated. 

Transactive Energy Controls Survive First Test in Pacific Northwest

For the past five years, a consortium of researchers, technology companies, and power utilities have been testing a novel power delivery system in the Pacific Northwest of the United States.

The Pacific Northwest Smart Grid Demonstration project was far reaching and had more than 50 experiments, but the most cutting edge was testing transactive controls for the power grid. The project was led by Battelle and funded by the U.S. Department of Energy. 

Transactive control involves an automated communication and control system connecting energy providers and users, who constantly exchange information about price and availability of power. When an energy provider predicts a surge in power demand, and therefore also higher prices, for example, it sends out this information as “transactive signals” to the rest of the network, including users. Based on these signals, smart grid technologies can react, reducing power use at the right time. The goal is improving reliability and efficiency, allowing for more dynamic balancing of resources, especially in regions that rely on high levels of renewables.

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Antineutrino Detectors Could Be Key to Monitoring Iran's Nuclear Program

President Obama has made it clear in a statement that the Iran nuclear deal signed yesterday was “built on verification.” Technology built to detect an elusive subatomic particle called the antineutrino could help.

The International Atomic Energy Agency wants a reactor-monitoring tool that is portable, safe, inexpensive, and remotely controllable. Antineutrino detectors, which give a peek into how much uranium and plutonium are in a reactor core, promise all of that.

The technology, which has been in the works since the early 2000s, has improved tremendously in the past five years, and it is now almost ready for practical use, says Patrick Huber, a physics professor at the Center of Neutrino Physics at Virginia Tech in Blacksburg. “Less than two years from now, you should have at least one maybe several types of antineutrino detector technologies that would work as nuclear safeguard detectors.”

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New Study Finds Feedback Loop Between Air Travel and Climate Change

Airplanes emit greenhouse gases that cause global warming. Now, a study published in Nature Climate Change suggests that air travel and climate change could actually be coupled in a loop. Changing wind patterns due to a warming climate could lengthen certain flight times, resulting in long-haul flights burning even more fuel and emitting yet more greenhouse gases.

Researchers at the Woods Hole Oceanographic Institution wanted to see how flying times between Hawaii and the western US coast were affected by jet-altitude winds. From a Department of Transportation public database, they got departure and arrival times for every single flight going back and forth between Honolulu and Los Angeles, San Francisco and Seattle for the past 20 years. That was a total of 250,000 flights operated by four major airlines.

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Wind Turbines Power Liquid-Air Energy Storage

One startup energy company is looking to reinvent not only wind energy, but also energy storage.

Keuka Energy recently launched a 125-kilowatt prototype vessel that uses its novel floating wind turbine design paired with liquid-air energy storage to create a steady source of electricity.

Unlike traditional wind turbines, which have three blades and a central gearbox, Keuka’s turbine is a pinwheel of aluminum blades that sits atop a floating V-shape platform containing liquid air.

The Florida-based company claims that its wind turbine design allows for larger turbines that could produce far more electricity. The world’s largest single offshore wind turbine is currently about 6 megawatts; Keuka says its full-size turbines could produce at least double that amount.

Liquid-air energy storage, also sometimes called cryogenic energy storage, is a long-term energy storage method: electricity liquefies air to nearly -200°C and then stores it at low pressure. When the energy is needed, the liquid air is pumped to a high level of pressure and heated to a gas state. The gas then drives a turbine.

Although it is an attractive energy-storage technology because of its long duration, liquid-air energy storage requires a significant amount of electricity to make the liquid air, limiting its usage by utilities. Keuka claims that because its design substantially reduced the cost by supplying the power directly from the turbines to the liquefaction equipment.

The company also says its wind turbine design is more cost effective, thanks to elimination of the gear box and the use of light-weight aluminum blades that cost less than 10 percent the price of traditional composite blades. Even if the technology is effective and can come in at lower costs, Keuka will likely face a long road to acceptance by the notoriously risk averse utility industry.

Keuka is not the only startup looking to advance liquid-air energy storage. In 2014, General Electric signed an exclusive global licensing deal with Highview Power Storage, a U.K. startup that makes utility-scale liquid-air energy storage systems.

Another similar technology that has gained more traction is compressed-air energy storage, which does not have the energy density of liquid air, but so far has proven more cost effective. Compressed air, while a cheap form of energy storage once built, is still expensive to build and geographically limited; underground caverns are needed to store the air.

Other startups are also looking offshore for cheap energy storage. Bright Energy is developing a system that would use offshore renewable energy to store compressed air in vessels in the ocean. Canadian startup Hydrostor also has a design to store compressed air underwater. 

If Keuka’s 125-kilowatt prototype is successful, it plans to launch a larger 25 MW demonstration project in early 2017.


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