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Green Flow Battery Based on Cheap, Nontoxic Reagents

Flow batteries are an interesting alternative to conventional batteries because they can store charges in the form of a liquid electrolyte that can be kept in tanks. Only the size of the tanks limits the amount of energy that can be stored. Utility companies and energy engineering firms have been eying these devices because they might replace storage batteries, devices that: have a limited lifetime; are known to be fire hazards; require metals such as lithium, that are limited in supply; and can only store energy in the electrode material, which has a fixed volume. What stands in the way of the wide implementation of flow batteries, in spite of the fact that they are commercially available, is that the compounds they use are expensive, toxic, and corrosive. Additionally, the energy storage capacity per unit volume of the electrolyte is low, typically just squeaking past 20 watt-hours per liter.

Recently IEEE Spectrum reported on a flow battery that has a better performance and uses a basic electrolyte instead of an acidic one, keeping a zinc compound in solution.  Now a team of researchers at Harvard University have reported in the 25 August issue of Science that they’ve created a version that uses two alkaline electrolytes that contain quinone and ferrocyanide—both widely available and non-toxic compounds—in solution. The researchers reported that after 100 charge-discharge cycles, the battery’s stored energy capacity had degraded less than 1 percent.  

Michael Aziz, who led the research group, realized that if the negative points of today’s flow batteries—cost and toxicity—could be overcome, the flow battery could become a commercially viable alternative for the storage now badly needed for intermittent energy sources such as solar and wind.  

“This looks like a compelling value proposition if you can find inexpensive chemicals that work well,” says Aziz.  “We noticed that there is a molecule in plants that takes the electrons from chlorophyll, and it forms an electron shuttle in photosynthesis that ports electrons over and over, without any sign of degradation. That is exactly the functionality you want for the battery,” says Aziz.  

However, the molecule did need some work; it was not soluble, and the reduction potential was not the right value.  “All these things can be changed,” he noted. “We found ways to render the molecule soluble, and change the voltage, so we have something that works and that is highly soluble.” 

The team made it clear that it was headed in this direction last year, when the researchers published a paper in Nature describing how they paired up this compound with bromine, which is a toxic substance. Aziz explains that, “We switched to alkaline chemistry because of the availability of a positive electrode material that is stable and soluble in base, but not in acid, and that is ferrocyanide.” Ferrocyanide is a widely available compound, used as a food additive and which, paradoxically, is not toxic because the cyanide groups are so strongly bonded to the iron atoms already present that they cannot attack the iron atoms in hemoglobin. “So now we have fulfilled our promise by coming through with non-toxic molecules on both sides [of the ion-selective membrane],” says Aziz. “We now have an entirely non-toxic chemistry.” 

Flow cells need electrolytes that keep these compounds in solution with extreme pH values so that electrons and ions can flow easily.  Most current flow batteries use acids, but the use of a base has other advantages. “Base is just less corrosive than acid, and this allows us to contain these electrolytes with much less expensive materials,” says Aziz.

At this point, about 95 percent of stored energy in the United States is in the form of water pumped up into a reservoir, which can be released to generate power by driving turbines when flowing back down. But in flat or arid areas, this storage option is not available, and it is here that flow batteries could play an important role, argues Aziz. “We are looking at a technology that can be used where pumped hydro cannot—in the middle of a city, on rooftops, near windfarms and solar farms,” he says.  However, reaching this goal will require further work.  “We need to prove that these molecules can last many thousands of cycles of oxidation and reduction, without doing anything else.” 

Is industry interested? When they published their first paper in Nature last year, there was a lot of interest from companies. According to Aziz, “Most of them said, this is really interesting, call us as soon you get rid of the bromine.”

Carbon Polluters Fund XPrize to Repurpose Their Emissions

XPRIZE—the organization behind grand technology challenges such as the race to space won in 2004 by SpaceShipOne and current contests to land a Lunar rover and a Star Trek-style medical tricorder—unveiled a competition today that tackles a more mundane yet critical challenge: transforming carbon dioxide emissions from power plants into saleable products to help slow or reverse climate change. The competition's $20 million kitty has been raised from major carbon emitters: a coalition of oil and gas producers producing high-carbon oil from Alberta’s oilsands, and New Jersey-based electric utility NRG Energy. 

Entrants will have until early 2020 to develop CO2 conversion technologies on two tracks: one targeting flue gas emissions from coal-fired power plants, and a second targeting the less concentrated emissions from natural gas-fired generators. The technologies that convert the most CO2 into products with the highest net value will win. 

XPRIZE Chairman and CEO Peter Diamandis said in a statement that the Carbon XPRIZE confronts the fact that our "age of unprecedented technological progress and prosperity” is powered primarily by fossil fuels. According to the statement, competing technologies could incorporate CO2 into such products as chemicals, cement and other building products, and transportation fuels. 

Some carbon dioxide is already being repurposed today, but the price is high. A few oil producers are using post-industrial CO2 as a working fluid to loosen up aging oil reservoirs, simultaneously boosting the flow of oil to the surface and storing the fossil carbon underground. Researchers in China are exploring a twist on such ‘enhanced oil recovery’ to produce water, proposing to sequester CO2 captured from a coal-fired power plant in Tianjin while yielding an estimated 1.4 million cubic meters of deep water annually.

Of course, burning the extra oil produced via enhanced oil recovery releases more fossil CO2, clawing back some of the environmental benefit. And a supply of CO2 for such projects is hard to come by due to the high cost of equipping power plants for carbon capture and operating the equipment.

The Carbon XPRIZE seeks to catalyze carbon capture by turning CO2 molecules into products with higher added value. Scientists are exploring the possibilities already. Austrian researchers have, for example, demonstrated the use of enzymes and electricity to convert COinto alcohol-based fuels. And last year a demonstration plant in San Antonio began capturing CO2 from a cement plant and converting it into minerals and chemicals, including sodium carbonate, hydrochloric acid and bleach.

Unfortunately the environmental benefits of synthesizing CO2 into something new remain dubious because capturing CO2 and chemically refashioning it requires considerable energy. In the case of the alcohol fuels, the energy requirements of the chemical processing completely negate the climate protection achieved by recycling CO2.

The ultimate irony of the Carbon XPRIZE is that it could turn out winners that still do not pencil out economically or environmentally. Meanwhile, the oil producers backing it via Canada’s Oil Sands Innovation Alliance, a Calgary-based trade group, are sitting on advanced production technology that promises to profitably slash their emissions at the source. 

Oilsands emissions are rising as the industry shifts from open-pit mines that scrape Alberta’s tarry bitumen off the surface to operations that attack deeper deposits by drilling wells and injecting steam underground to melt the bitumen and pump it to the surface. But options that could shrink that footprint exist. 

Calgary-based oilsands process developer N-Solv has proven the effectiveness of a low-energy process at a 250 to 300 barrel-per-day demonstration site near Fort McMurray that uses butane to dissolve bitumen instead of steam. This month, the company celebrated production of its 60,000th barrel of heavy oil since starting the demonstration plant in 2014, and announced it had won its own prize—a place among 2015 honorees for Canada's Clean50 Awards

Eliminating steam production from natural gas makes the overall process cheaper while cutting carbon emissions per barrel by as much as 80 percent. “We can be as clean or cleaner than conventional oil,” says John Nenniger, N-Solv’s founder and chief technology officer. 

Oilsands operators have conducted their own experiments with solvent-based production over the past five years, but implementation is lagging. Nenniger says oilsands producers neglected the technology when oil prices were high because they could make a profit with the older and dirtier steam technology. Weak Canadian climate policies meant they were not obligated to take a risk on the cleaner approach. And now that oil prices are low and oilsands projects are losing money, capital for new operations is scarce. 

”It’s so frustrating from my perspective because every other industry is so aggressively competing to get to the bottom of the supply cost curve,” says Nenniger. “The oilsands industry says stuff, but they don’t actually do anything. Investment has been 10 to 20 fold below what it should have been.”

Canadian Prime Minister Stephen Harper pulled his country out of the Kyoto Protocol in 2011, arguing that complying with the treaty's prescribed greenhouse gas reductions would hurt Canada's energy-intensive economies. Change may be coming, however. Harper, who hails from Alberta and has strong support from the oil and gas sector, finds himself in a tight race for re-election in October. 

Thomas Mulcair of the New Democratic Party, a former Quebec environment minister who is leading in nationwide polls, unveiled plans this weekend for a cap and trade program to cut carbon emissions 80 percent by 2050—the same goals established by climate policy leaders such as the European Union and California. As of 2013, Canada's emissions were 18 percent above 1990 levels.

Scotland and Ireland Consider a Linked Renewable Energy Future

The governments of Scotland, the Republic of Ireland, and Northern Ireland plan to coordinate the development of offshore renewable energy projects in their shared ocean water. The goal is to build an interconnected network of offshore wind, tidal, and wave generation and transmission in the Irish Sea, the straits of Moyle, and the western coast of Scotland.

The countries launched a feasibility study five years ago. It culminated last week in a series of reports including: a business plan; recommendations for how to implement projects; three proposed projects to serve as initial proof of concepts; and a spatial plan that provides guidance to potential developers regarding the best places to install offshore wind, tidal, and wave energy projects.

The area between Ireland and Scotland has the potential to generate around 16.1 gigawatts of renewable energy, including 12.1 GW from offshore wind and 4.0 GW from wave and tidal energy. The ISLES project's initial goal is to connect 6.2 GW of that potential generation by 2020.

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Researchers Tweak Artificial Photosynthesis for More Efficient Hydrogen Production

A team of researchers from Germany and the U.S. have announced a new record value of 14% for the efficiency of water splitting by solar energy in a single cell.  The previous record, 12.4%, was achieved 17 years ago by the National Renewable Energy Laboratory  and the value in subsequent experiments with a technology called artificial photosynthesis has hovered around that figure.  The researchers published this result last week in Nature Communications.

These figures should not be confused with the light conversion percentages of photovoltaic cells, explains Thomas Hannappel of the Technical University Ilmenau in Germany, who was the academic advisor for the researchers.   “The percentages refer to the hydrogen efficiency,  that is you compare the light energy captured by the photovoltaic cell to the energy that can be supplied by burning the produced hydrogen,” says Hannappel. 

Artificial photosynthesis can be achieved by two different approaches:  The first approach is a photovoltaic cell that supplies the current to the electrodes in a separate cell that splits water molecules into their constituents, hydrogen and oxygen.  In the second approach, the photovoltaic cell also acts as an electrode in contact with water, and the voltage it produces splits the water directly.   Having these two functions, photoelectricity generation  and electrolysis into one unit makes it more usable, says Hannappel.  “We have a greater range for cost reduction with one unit than with two different units,” says Hannappel. 

However, still a lot of research will be necessary to reach this stage.  “One of the referees during the publication process asked us, ‘Is this just a matter of dunking a high-efficiency PV cell into a solution and then getting out hydrogen?’ ” remembers Matthias May of the Helmholz Zentrum Berlin, whose doctoral dissertation dealt with this research.  Indeed, the fact that you have to deal with a liquid-solid interface, the electrolyte, and the photosensitive semiconductor and a its interface with the catalyst surface is not a trio that gets along easily with each other. 

First, the researchers opted for using III-V semiconductors for the photovoltaic material.  Not the cheapest and experimentally easiest choice, but these materials, made from elements residing in the third and fifth column of the periodic table, are more efficient in converting light into electricity than silicon.  To achieve the required voltage, the researchers used tandem cells in which two layers with different band gaps convert photons from the entire solar spectrum into electricity.  

Now, to make the two percent improvement required some experimental ingenuity.  “We tuned the surface of our III-V solar cell on a subnanometer scale, transforming aluminum-indium phosphide into phosphate species and then depositing the catalyst on top,” says May.  “What was important here was that the photochemical transformation process was all done in situ.  This means that this interface never saw ambient air before the catalyst was deposited. That was very important because otherwise you will get charge-carrier recombination centers at the interface and this will reduce your overall device efficiency.”

Also the stability of these devices, complicated by chemical interactions between the electrolyte and the photovoltaic surface is still a far cry from current voltaics, although their prototypes ran for 40 hours.  “One year ago we had stabilities of a couple of seconds, and we have improved that by three-four orders of magnitude, so we are optimistic that we can improve that by another three or four orders of magnitude.”

Ultimately, higher efficiencies, starting with 18–20% will allow the conversion of solar energy into hydrogen  to become part of the burgeoning hydrogen economy.  “In Germany we have a company that uses windmills connected to electrolyzers and they inject the hydrogen directly into the methane gas grid; you can do that up to five volume percent without changing the grid.  This also forms some storage capacity if you have an overcapacity of electricity in the grid,” says May.

Photonic Crystal Uses Coldness of the Universe to Chill Solar Panels on Earth

Last December, researchers at Stanford University developed a passive radiator that uses outer space as a universe-size heat sink. It absorbs ambient heat and then emits it at a very specific infrared band (between 8 and 13 micrometers), for which the Earth’s atmosphere is completely transparent. So the radiator can transfer the heat entirely off-world.

Stanford's radiator is cheap to produce (or so they say), but it would be fighting for rooftop space with all the solar panels that we (should) have up there. In work published today in PNAS, the Stanford researchers describe the performance of a prototype photonic crystal cooling system that can sit on top of a solar cell and cool it by up to 13 degrees Celsius—boosting the amount of electricity that it generates.

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Wearable Uses Your Local EM Field to Track Your Electronics Use

A prototype of a wearable device can sense what appliance you’re using. Engineers at the University of Washington developed MagnifiSense, a wrist-worn magnetic sensing system that tracks your interaction with specific devices, such as a microwave or hair dryer. Based on which device is detected, the system infers what activity you’re performing: Turning on a stove implies that you’re cooking, for example.

Tracking an individual’s daily activity could help monitor and perhaps reduce a user’s energy footprint, or it could feed data to smart home applications and provide safety alerts for the elderly. The Washington team described MagnifiSense and its potential uses in research [pdf] presented at the 2015 ACM International Joint Conference on Pervasive and Ubiquitous Computing in Japan last week.

MagnifiSense works because each appliance generates a distinct electromagnetic radiation pattern. MagnifiSense uses off-the-shelf magneto-inductive sensors to capture a wide spectrum of frequencies near the user. This allows the wearable device to identify the radiation of the particular components—motors, rectifiers, and various modulators—that make up the pattern. Using signal processing and machine learning techniques, the system can use the combination of components to distinguish one device from another.

 Edward Wang, lead researcher and a PhD student in electrical engineering at the University of Washington gave a hairdryer as an example:

The frequency component of a hairdryer is that there’s a motor that spins, so there’s going to be some changing frequency that has to do with the motor’s speed… There’s also the power that it draws, which is 60 Hz in America. The 60 Hz component can be seen in our signal. So, if it doesn’t have a 60 Hz component signal, then it’s not plugged into the wall.

These type of characteristics, also known as domain knowledge, are gathered into a feature set, which is similar to a template, says Wang. After hundreds of different hairdryer templates are fed into the system, it learns to identify the behavior of a hairdryer. Then, when the template of an unknown device is fed into the system, it compares it against existing templates to determine a match.  

The team studied MagnifiSense’s performance in 16 homes and on 12 commonly used appliances in the kitchen, living room, and bathroom. It also studied the user’s interaction with various devices. In a 24-hour period, MagnifiSense successfully identified 25 of the 29 interactions.  

Although this technology seems promising, researchers still need to work out a few kinks. People tend to interact with multiple electronics simultaneously. But, the current prototype can’t detect when multiple electronics are used concurrently.

“Due to the nature of the signal, they add linearly,” Wang says. “The sensor sees A plus B plus C.” This means that if you turn on the stove and also use the blender, the system detects the appliance closest to you- not both. He also says they’re trying to miniaturize the wearable device. 

Japanese Paper Cutting Trick for Moving Solar Cells

To maximize the amount of electricity that solar cells generate, solar panels can be tilted to track the position of the sun over the course of a day. Conventional solar trackers can increase yearly energy generation by 20 to 40 percent, but they can be costly, heavy and bulky, limiting their widespread implementation.

Now materials scientist Max Shtein and his colleagues at the University of Michigan at Ann Arbor have developed novel solar cells that integrate tracking into their design. The design involves a variation of origami known as kirigami, which uses both folding and cutting to create unique structures. They detailed their findings in the 8 September online edition of the journal Nature Communications.

The scientists cut kirigami designs into a 3-micron-thick flexible crystalline gallium arsenide solar cells mounted on plastic sheets. A solar cell array of this type can tilt in three dimensions in a highly controllable manner when its edges are tugged. So a quick pull can make it flex so that it is at the best angle for catching rays.

The researchers found that their new devices could generate roughly as much power as solar cells mounted on conventional trackers. Moreover, the kirigami trackers proved to be electrically and mechanically robust, with no appreciable decrease in performance after more than 300 cycles of activity.

Shtein and his colleagues suggest that kirigami solar panels could be simple, inexpensive and lightweight, and have widespread rooftop, mobile, and spaceborne applications. They added that kirigami systems might also be useful for phased array radar and optical beam steering.

The scientists are now exploring whether mounting solar cells onto more durable materials such as spring steel could make kirigami systems even more robust. 

Artificial Leaf Is 10 Times Better at Generating Hydrogen from Sunlight

A "hydrogen economy" sounds just about as green and eco-friendly as it gets. Fuel cells that combine hydrogen with ambient oxygen in the air can generate electricity with naught but pure water as a byproduct—which is great if you hate pollution and are thirsty. The problem we face now is the source of our hydrogen: the vast majority of it comes from fossil fuels, specifically natural gas. And while transforming methane into hydrogen is 80 percent efficient, that other 20 percent is carbon dioxide.

The vast majority of the accessible clean hydrogen on Earth is locked up with oxygen in water, but breaking apart H2O into an O and a useful H or two isn't a particularly environmentally-friendly or efficient process to get involved in. The fantasy is an "artificial leaf," a passive, inexpensive thing that you can stick in water and expose to sunlight, then watch as it bubbles off all the hydrogen and oxygen you need. People have been working on these, but Caltech has just made an enormous amount of progress with an artificial leaf that, according to the researchers, "shatters all of the combined safety, performance, and stability records for artificial leaf technology by factors of 5 to 10 or more."

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A city skyline with imaginary wind turbines just off shore.

Renewable Energy is Good for Your Health

Renewable energy projects and energy efficiency measures—particularly those that replace coal-fired power plants—will not only decrease carbon emissions but may also have major health implications worth millions of dollars, according to researchers at Harvard University.

Public health experts evaluated the impact of four different renewable energy or energy efficiency installations in six locations in the mid-Atlantic and Great Lakes regions and came up with a model to simulate and compare the climate and health benefits of each of the 24 scenarios. Depending on the site and installation, they found that benefits ranged from US $5.7 million to $210 million per year.

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Concentrator Photovoltaics: The Next Step Towards Better Solar Power

Today’s concentrator photovoltaic (CPV) technologies have shown promising potential for more efficient solar power. The latest systems are said to be capable of handling the power of a hundred suns. Yet prototypes have failed to compete with cheaper flat panel solar systems that dominate the market. The U.S. Department of Energy’s Advanced Research Projects Agency (ARPA-E) is determined to push CPV to the next level. On 24 August, at the Clean Energy Summit, U.S. President Barack Obama and Energy Secretary Ernest Moniz announced a program called MOSAIC that will invest $24 million into CPV solar technology development.

Why can’t today’s CPV systems compete? The concentrators can only convert direct sunlight into energy, missing out on the large fraction of sunlight diffracted by clouds and the atmosphere. Manufacturing costs of concentrator apparatuses have also prevented CPV from reaching mass production.

That’s where the MOSAIC initiative comes in. The 11 new CPV programs under MOSAIC’s umbrella are investigating an array of system designs to address cost-efficiency and performance challenges. The list of projects include economical micro-PV cell construction, waveguiding solar concentrators, and single-junction cells that will maximize concentration under indirect and diffuse sunlight.

“ARPA-E is supporting new technology that can help the industry progress even more, but even where it is today is quite exciting,” says Sarah Kurtz, a research fellow working on CPV technology (separately from the MOSAIC effort) at the U.S. National Renewable Energy Laboratory (NREL) in Colorado.

For a large-scale commercial flat plate solar panel system, efficiency is approximately 16 to 20 percent, while a typical CPV system is 25 to 30 percent. In engineering labs, efficiency test results show that the gap between CPV technology and flat planel photovoltaics is even greater. Research groups have created CPV cells that convert more than 40 percent of the light that strikes them to electric current—the highest marks received in testing environments. Three of these groups’ systems have even passed the 46 percent mark.

“This means that these results are very repeatable,” says Keith Emery, a principal scientist who measures solar cell efficiency at the National Center for Photovoltaics at NREL. “I wouldn’t be surprised that by the next two or three years, an individual research group will reach 50 percent efficiency. Fifty percent is a realistic goal that people have on the drawing board.”

CPV maximizes efficiency by using multiple optical elements such as mirrors and lenses to reflect light into a super concentrated beam that is aimed at a solar cell. Machinery adjusts the panels throughout the day so that the cells are exposed to a maximum amount of direct sunlight. The technique is similar to the way you would move a magnifying glass while burning your name into a piece of wood, explains Kurtz.

The optical elements make it possible to use smaller, higher performance solar cells. The miniaturized cells make it easier to modulate their movement to prevent overheating and degradation. Some labs have even constructed cells as small as 1 square millimeter; they can generate more power in less space than flat panels can.

The next push is to make CPV materials that are even greener and cheaper than flat plate photovoltaics. Engineers are testing mirrors constructed from recyclable plastic, with aluminum-based reflective coatings, says Kurtz.

As the energy industry slowly transitions old fossil fuel plants into photovoltaic and other renewable power plants, solar energy can become a larger part of the electric grid.

“There is a rumor that solar is the technology of the future,” Kurtz says. “It has grown a lot, but it is still a minuscule part of the electricity we use.” While photovoltaics provide only about 1 percent of the electricity generated in the U.S., the rate of solar installation is increasing every year. “If we maintain industry growth rates long enough, solar could be at something like 25 percent of the world’s electricity production,” says Kurtz.


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