2 for 1 in solar power
by Staff Writers
Cambridge UK (SPX) Nov 19, 2013


2 for 1 in solar power

Left: This shows laser set-up in the lab in Cambridge. Right: This is the Celestia sun. Credit: Brina Walker.
Solar cells offer the opportunity to harvest abundant, renewable energy. Although the highest energy light occurs in the ultraviolet and visible spectrum, most solar energy is in the infrared. There is a trade-off in harvesting this light, so that solar cells are efficient in the infrared but waste much of the energy available from the more energetic photons in the visible part of the spectrum.
When a photon is absorbed it creates a single electronic excitation that is then separated into an electron and a positively charged hole, irrespective of the light energy. One way to improve efficiency is to split energy available from visible photons into two, which leads to a doubling of the current in the solar cell.
Researchers in Cambridge and Mons have investigated the process in which the initial electronic excitation can split into a pair of half-energy excitations. This can happen in certain organic molecules when the quantum mechanical effect of electron spin sets the initial spin 'singlet' state to be double the energy of the alternative spin 'triplet' arrangement.
The study, published in the journal Nature Chemistry, shows that this process of singlet fission to pairs of triplets depends very sensitively on the interactions between molecules. By studying this process when the molecules are in solution it is possible to control when this process is switched on.
When the material is very dilute, the distance between molecules is large and singlet fission does not occur. When the solution is concentrated, collisions between molecules become more frequent. The researchers find that the fission process happens as soon as just two of these molecules are in contact, and remarkably, that singlet fission is then completely efficient-so that every photon produces two triplets.
This fundamental study provides new insights into the process of singlet fission and demonstrates that the use of singlet fission is a very promising route to improved solar cells. Chemists will be able to use the results to make new materials, say the team from Cambridge's Cavendish Laboratory, who are currently working on ways to use these solutions in devices.
"We began by going back to fundamentals; looking at the solar energy challenge from a blue skies perspective," said Dr Brian Walker, a research fellow in the Cavendish Lab's Optoelectronics group, who led the study.
"Singlet fission offers a route to boosting solar cell efficiency using low-cost materials. We are only beginning to understand how this process works, and as we learn more we expect improvements in the technology to follow."
The team used a combination of laser experiments - which measure timings with extreme accuracy - with chemical methods used to study reaction mechanisms. This dual approach allowed the researchers to slow down fission and observe a key intermediate step never before seen.
"Very few other groups in the world have laser apparatus as versatile as ours in Cambridge," added Andrew Musser, a researcher who collaborated in the study. "This enabled us to get a step closer to working out exactly how singlet fission occurs."

Small-Wind Power Market to Reach $3 Billion by 2020
by Staff Writers
London, UK (SPX) Nov 27, 2013


Small Wind Power Market to Reach 3 Billion by 2020

With growing incentives announced by various governments and larger end-user awareness, the small-wind power market is expected to increase massively, from $609m in 2012 to $3 billion by 2020, at a Compound Annual Growth Rate (CAGR) of 22%, says research and consulting firm GlobalData.
According to the company's latest report*, the global small-wind turbine cumulative installed capacity is also expected to witness a significant increase from 728.3 Megawatts (MW) in 2012 to 4,644.7 MW by 2020, at a CAGR of 26.1%.
Additionally, China, the US and UK contributed to more than 80% of the global small-wind power installed capacity in 2012, with 266 MW, 216 MW and 118 MW, respectively.
Prasad Tanikella, GlobalData's Senior Analyst covering Power, says: "Small-wind power has huge potential in China, due to the large rural population and the requirement for distributed power systems. The country also has more than 80 small-wind turbine manufacturers, which produce the largest number of these turbines.
"Still, the UK was the fastest growing small-wind power player in 2012, installing more than 50 MW. Its market is expected to grow further due to financial incentives under the renewable obligation, the implementation of Feed-in Tariff policies, and streamlining of administrative procedures."
Although the future for small wind looks promising, the market could face some obstacles in the form of economic slowdown, along with zoning and permitting challenges. Further hindrance could be caused by low public awareness, lack of net-metering programs and certification issues.
"Poor permitting practices and unnecessary restrictive regulations are the major market barriers discouraging customer interest and investment. Streamlining the permitting process will be crucial towards ensuring that the growth of wind installation is not hampered by administrative issues," Tanikella concludes.

Copper promises cheaper, sturdier fuel cells
by Staff Writers
Durham NC (SPX) Nov 28, 2013

Copper promises cheaper sturdier fuel cells

Copper adorns the Statue of Liberty, makes sturdy, affordable wiring, and helps our bodies absorb iron. Now, researchers at Duke University would like to use copper to transform sunlight and water into a chemical fuel.
Converting solar energy into storable fuel remains one of the greatest challenges of modern chemistry. One of the ways chemists have tried to capture the power of the sun is through water splitting, in which the atoms of H2O are broken apart so the hydrogen may be collected and used as fuel. Plants do this naturally through photosynthesis, and for half a century, scientists have tried to recreate that process by tinkering with chemical catalysts jumpstarted by sunlight.
Indium tin oxide (ITO) is one material they've commonly tried to use. Researchers prefer it for its transparency - which allows sunlight to pass through and trigger the water-splitting reactions - and its ability to conduct electricity. But ITO is far from an ideal material.
"Indium is not very abundant," said Ben Wiley, assistant professor of chemistry at Duke University. "It is similar in abundance to silver in the earth's crust." As a result, solar fuel cells using ITO will likely remain expensive and uncompetitive with conventional energy sources like coal and natural gas, he said.
Wiley's lab has created something they hope can replace ITO: copper nanowires fused in a see-through film. The team - including two postdoctoral researchers, a graduate student, and a former graduate student from Duke - published their new approach last month in the chemistry journal Angewandte Chemie.
Copper is 1000 times more plentiful and 100 times less expensive than indium. Copper nanowire catalysts also cost less to produce than their ITO counterparts because they can be "printed" on pieces of glass or plastic in a liquid ink form, using a machine that functions much like a printing press. ITO production, by contrast, requires large, sequential chambers of pumps and vacuums that deposit a thin layer of indium atoms at a far slower rate.
The copper nanowire films consist of networks of microscopic metal rods, the properties and applications of which Wiley's lab has studied for years. The nanowires provide a high surface area for catalyzing chemistry, and Wiley's team experimented with coating them in either cobalt or nickel - metals that serve as the actual chemical catalyst.
Even with a coat of cobalt or nickel, the nanowire films allow nearly seven times more sunlight to pass through than ITO. The films are also flexible, leading Wiley to imagine the completed fuel cells one day being attached to backpacks or cars.
In the meantime, engineering and chemistry challenges remain. The nanowire films carry out only one half of the water-splitting equation, a process called water oxidation. The other half of the reaction involves using the electrons obtained from water oxidation to reduce water to hydrogen. Wiley's team expects to publish their work on this process in the coming year.
"A lot of groups are working on putting together complete devices to generate fuels from sunlight," he said, but "the efficiencies and costs of these systems have to be improved for them to get to commercial [production]."
Wiley noted that solar energy production is just one application of the copper nanowire films they study. The nanowires also show promise for use in flexible touch screens, organic LED (or OLED) lights and smart glass.
"Optically Transparent Water Oxidation Catalysts Based on Copper Nanowires," Zuofeng Chen, Aaron Rathmell, Shengrong Ye, Adria Wilson, Ben Wiley. Angewandte Chemie, October 18, 2013. 10.1002/ange.201306585.

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