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An artist's rendering of EMBR Labs' thermoelectric wearable by Italian designer Niccolo Casas.

Wristify: Thermoelectric Wearable Would Reduce Energy Consumption

Last week Computex, the largest ICT trade show in Asia, was accompanied by record breaking heat (38.7ºC). So it should be no surprise that Wristify, a thermoelectric bracelet, was popular with visitors to the Taipei show.

Wristify, invented by MIT startup EMBR Labs, works because the wrist is rich with blood-flow, so the cold provides quick relief. Similarly, it could also rapidly warm up a shivering skirt-wearing lady (your reporter) who’d been in an air-conditioned room for hours.

“… anytime you’re feeling too hot, too cold, stressed, or anything like that, you can basically control the sensation that you have on your skin and that can produce the overall effective, feeling better,” says co-founder David Cohen-Tanugi. 

The watch-shaped prototype wearable is manually controlled, letting the user adjust the temperature to their preferred level.  The team is adding intelligence so that a future product will be able to automatically adapt, according to Cohen-Tanugi. And the company is in the final preparations for a public launch of product pre-orders, which should happen by the end of September, he says.

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A device combines a silicon solar cell with a triboelectric generator that can harvest wind energy.

Solar and Wind Energy From the Same Device

A device that can simultaneously harvest energy from both the sun and wind might one day help generate power for "smart cities," researchers say.

Cities are growing smarter as networks of electronics help them monitor and control infrastructure and services. Ideally, these devices would be powered by renewable energy sources such as the sun and wind. Solar energy can come from rooftops and into even windows. However, large amounts of wind energy often gets wasted in cities—conventional wind turbines are usually not suited to urban areas because of their size.

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A wind turbine in China.

Why China's Wind Energy Underperforms

China accounted for 36 percent of global investment in renewable energy last year, pouring $102.9 billion into non-hydro renewables such as wind and solar power. The country is a laggard, however, in maximizing return on renewable energy dollars, especially for wind power. China closed out 2015 with nearly twice the installed wind power capacity of the U.S., yet last year it generated less wind energy.

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Photo: You Zhou

Perovskites Key to New Type of Hydrogen Fuel Cell

Crystals known as perovskites promise to revolutionize solar cells. Now researchers have found that they could improve fuel cells as well.

Fuel cells convert the chemical energy stored in fuels such as hydrogen into electricity. They do so by reacting the fuel with oxygen or another oxidizing agent that can strip electrons from the fuel. An electrolyte—commonly a polymer or ceramic—interposed between the fuel and oxidizer helps shuttle ions within the fuel cell.

Fuel cells are typically more efficient and environmentally friendly than heat engines, such as the internal combustion engines that usually power cars. However, fuel cells are often limited by how well their electrolytes can prevent electrons from leaking through them at the interface where the fuel and the oxidizing agent meet. Such electron conduction not only reduces fuel cell power output, but it can also lead to catastrophic fractures in the electrolyte.

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Plexiglass Gel Boosts Nanowire Battery Lifespan

A new battery material based on nanowires that can be recharged hundreds of thousands of times, could lead to commercial batteries for smartphones, laptops, appliances, cars, and spacecraft that have greatly enhanced lifespans, researchers say.

Scientists have long sought to create batteries using nanowires—strands only nanometers, or billionths of a meter, wide. Their tremendous surface area when compared with their volume makes them spectacular at storing and transferring electrical charge.

“Nanowires enable battery technology with higher power; you're able to get more current out of a battery the same size as [today’s] batteries, and make batteries smaller and get the same performance out of them as [the ones that are commercially available],” says Reginald Penner, an electrochemist at the University of California, Irvine.

The one drawback of nanowires has been their fragility, Penner says. Their thinness increases their susceptibility to dissolving and fragmenting under repeated cycles of discharging and recharging.

But now, Penner and his colleagues have developed a way to counteract that fragility. The researchers coated gold nanowires in manganese dioxide shells and formed an electrode by encasing hundreds of these nanowires together in a gel made from the same molecule found in acrylic glass. “The gel has the consistency of peanut butter,” Penner says. The scientists detailed their findings in 20 April online edition of the journal Energy Letters.

In experiments, the scientists cycled their electrode on and off up to 200,000 times over the course of three months without detecting any loss of energy storage capacity or power and without fracturing any nanowires. Typically, nanowire-based battery materials die after 7,000 or so cycles at the most, the researchers say. “It's surprising that such a simple change can trigger such a profound change in cycle stability,” Penner says.

The researchers suspect that the highly viscous and elastic acrylic glass plasticizes the manganese oxide shell, granting it flexibility and preventing it from cracking. A control sample of gold and manganese nanowires without the acrylic glass lasted only about 8,000 cycles.

Future research will explore if using a gel electrolyte can enhance other kinds of nanowires, Penner says. Subsequent work can also investigate other kinds of gels, and determine what effects will result from modifying the viscosity and other properties of the gels.

Kyushu Earthquake Swarm Raises Concerns Over Nuclear Plant Safety

The populous island of Kyushu in southwest Japan has been shaken by hundreds of earthquakes and aftershocks over the past eight days, and there is no immediate end in sight to Mother Nature’s upheavals.

The tremors have impacted manufacturing for some companies in the auto and electronics industries, while concerns are growing over the safety of Japan’s two active nuclear reactors (the only two presently online), which are located about 120 km south of where the main shaking is occurring.

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Will Nanophotonics Save Solar Power Tech?

Nanophotonic technology could be the key to driving up the efficiencies of solar cells, making them feasible for widespread global deployment, say researchers from the FOM Institute for Atomic and Molecular Physics (AMOLF) in the Netherlands.

The researchers published a review article in Science today describing current solar technologies and their limitations with regards to efficiency. Silicon-based solar, which is now considered a mature technology, occupies about 90 percent of the photovoltaic market, the researchers wrote. Yet, over the last few years, silicon solar cells have realized only modest gains in efficiency, stalling out in the 20-percent range.

But, according to lead author Albert Polman, advances in nanophotonics could help increase efficiencies for single-junction solar cells to 40 percent and higher, and do so cost effectively. In addition, he said, the technology could be compatible not just with silicon, but any type of solar material.

“It's really an upcoming field,” Polman says.

Efficiency and cost are the two main barriers on solar, and often, one is compromised for the sake of the other, Polman says. Using less material, such as for thin-film solar cells, brings costs down, but drags efficiency down right along with it.

Nanophotonics can be applied to existing solar technologies to harness light more effectively to increase efficiency.

When sunlight hits a solar panel, a good amount of the potential energy is lost due to it being reflected and scattered, Polman says. But nanostructures incorporated into a panel can re-direct the scattered light within the solar cell, “so that the light travels back and forth within the cell and is trapped inside it,” he adds.

In the research described in the Science article, Polman's team calculated that the theoretical maximum efficiency for a single-junction monocrystalline silicon solar cell is 29.4 percent, although the majority of commercial silicon panels are multicrystalline silicon, which have efficiencies of around 20.8 percent. But that’s on paper. Thus far, the highest recorded experimental efficiency is 25.6 percent for monocrystalline silicon and 21.3 percent for multicrystalline silicon.  

Other materials don't fare much better. Solar cells made from gallium arsenide (GaAs) have the efficiency record for single-junction solar cells at 28.8 percent, but GaAs solar cells are expensive and mostly have niche applications for space and satellite technology, Polman says.

Meanwhile, less expensive materials like thin-film silicon, dye sensitized titanium dioxide, and organic solar, have not broken the 12-percent-efficiency mark.

Nanophotonic technology can help, though. Using printing techniques, nanstructures with improved light harnessing properties can be printed onto silicon-based solar cells, he said. Alternatively, cells can be designed with nanstructures incorporated into them from the beginning.

Polman's lab is currently conducting small-scale experiments using a printing technique to layer nanoscale structures onto silicon solar panels, he says, and is in the midst of building larger panels to test in the field.

Incorporating such nanostructures into silicon cells could help silicon reach beyond its maximum efficiency, but even greater gains will be realized when solar cells are built that combine different materials with nanostructures.

For instance, perovskite has recently been touted as a promising material for solar cell technology; demonstrations have shown that it can reach efficiencies of 20 percent. Polman says that layering perovskite on top of silicon could provide further advantages since the two materials capture different wavelengths of light. Earlier this year, researchers demonstrated that layering perovksite on top of a silicon solar cell boosted the efficiency by 7.3 percent. 

Incorporating nanostructures could provide a further boost by allowing researchers to “engineer the scattering of the light in a clever way,” he says.

Looking ahead, Polman says he envisions solar cells that make use of not just two materials, but three or four materials with complementary properties and nanophotonics to make the most use of the incoming sunlight.

“Further advances in nanophotovoltaics will lead to enhanced photocurrents, and thus enhanced efficiency, in several different PV materials and architectures,” the AMOLF team wrote, enabling “very large-scale penetration into our energy system.”

Graphene Could Help Generate Power From Rain

Solar cells could someday generate electricity even during rainshowers with the help of graphene, scientists say.

Rain helps solar cells operate efficiently by washing away dust and dirt that block the sun’s rays. Still, photovoltaic cells depend on light to produce electricity, and so generate a negligible amount of power when there are clouds overhead.

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Stamp-Size Gravity Meter Could Have Big Impact On Oil Exploration

To find buried oil reserves, surveyors have for decades used gravity meters, or gravimeters, along with other instruments. Gravimeters are hypersensitive versions of accelerometers: They measure extremely tiny changes in the acceleration due to gravity. These nanoscale changes can happen because of the presence of subterranean geological features like oil wells. The best gravimeters in use today are the size of a shopping basket, weigh a few kilograms, and cost around US $100,000, which limits their use.

But a new postage stamp–size device developed by Scottish researchers could make oil exploration faster, easier, safer, and more economical.

The new microelectromechanical (MEMS) device, along with all of its electronics, fits in a shoebox. And according to Richard Middlemiss—the physics and astronomy graduate student at the University of Glasgow who, along with other researchers at the school’s Institute for Gravitational Research, created the gadget—it could be shrunk down to the size of a tennis ball.

The team described the breakthrough in a paper recently published in Nature. They note that the gravimeter could be made in bulk from silicon wafers, so it should cost no more than a few thousand dollars.

Right now, oil surveying is done by driving or flying low over areas with a bulky gravimeter, measuring gravity’s effect on a mass attached to a string. Such surveys can’t assess rough terrain and “are expensive to do because of people time,” Middlemiss says.

He adds that, “With small, low-cost gravimeters, you could instead leave a network of sensors around a whole site for months.” He also imagines swarms of drones carrying ultra-light tennis-ball-size gravimeters flying low over otherwise inaccessible areas to do oil prospecting. “Instead of buying one device, you could buy a hundred; that would change the way surveys are carried out,” he says.

Middlemiss, University of Glasgow professor Giles Hammond, and their colleagues pushed gravity measurement forward by shrinking things down to the micrometer level. They carved a 15-millimeter-by-15-millimeter-by-7-micrometer piece of silicon to form a rectangular central mass attached to a square frame with three 7-µm-wide springs. The frame is hung between a white LED and a photodiode so that when the mass moves due to gravity, its shadow falling on the photodiode changes. The result: detectable changes in current.

The design is similar to the MEMS accelerometers used in smartphones. But the new gravimeter is a thousand times as sensitive as those, allowing it to detect extremely small changes in gravity.

To test the device, the team bolted the box to the floor in their building’s basement and used it to measure Earth tides, movements of the Earth’s crust due to the gravitational pull of the sun and moon. As the crust moved up and down by about 40 centimeters over the course of a day, changes in gravity moved the silicon mass in the gravimeter by 16 nanometers. That sensitivity was partly due to the thin springs, but also because the researchers enclosed it in a copper shield and vacuum box and maintained the temperature around it to within 1 milliKelvin.

Still, the device isn’t quite as sensitive as commercial gravimeters, Middlemiss says. So the researchers are working to improve its sensitivity even as they make it smaller. Later this year, they plan to test it in the field alongside its commercial counterparts. The team says it is now in talks with a geophysical exploration company and a survey instrument maker to take the technology closer to commercialization.

Besides oil exploration, the smaller, cheaper gravimeters could open up many other applications, including monitoring volcanoes by measuring magma levels under the crust, and studying geological formations and buried archeological features. As Hazel Rymer of The Open University puts it in an accompanying news and views piece: “Once these instruments become commercially available, the applications will be limited only by the user's imagination.”


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