Resource World Magazine

A LT ER NATI V E EN ER G Y R E VI E W Developments in Alternative Energy by Jane Bratun RESEARCHERS DEMONSTRATE POSSIBLE HUGE LEAP IN SOLAR PANEL EFFICIENCY Researchers at the Massachusetts Institute of Technology (MIT) have successfully demonstrated a technique that allows a photon to knock two, rather than the usual one, electrons loose. According to a press release, the MIT team was able, for the first time, to perform a successful proof of principle, known as singlet exciton fission. An exciton is the excited state of a molecule after absorbing energy from a photon. In a standard photovoltaic (PV) cell, each photon knocks loose one electron inside the PV material. That loose electron then can be harnessed through wires to provide an electrical current. But, in the new technique, each photon can instead knock two electrons loose. This makes the process much more efficient. In a standard cell, any excess energy carried by a photon is wasted as heat, but, in the new system, the extra energy goes into producing two electrons instead of one. While others have previously "split" a photon's energy, they have done so using ultraviolet light, a relatively minor component of sunlight at the earth's surface. The new work represents the first time this has been accomplished with visible light, laying a pathway for practical applications in solar PV panels. Because this was a first proof of principle, the team has not yet optimized the energy-conversion efficiency of the system, which remains less than 2%. But, improving that efficiency through further optimization should be a straightforward process, the researchers say. While today's commercial solar panels have an efficiency of at most 25%, a silicon solar cell harnessing singlet fission should make it feasible to achieve efficiency of more than 30%, researchers say – a huge JUNE 2013 leap in a field typically marked by slow, incremental progress. In solar cell research people are striving "for an increase of a tenth of a percent." The research was performed in the Center for Excitonics and supported by the US Department of Energy. MIT has filed for a provisional patent on the technology. WASTE SULFUR MAY IMPROVE BATTERIES FOR ELECTRIC VEHICLES According to a press release from the University of Arizona (UA), a new chemical process can transform waste sulfur into a lightweight plastic that may improve batteries for electric cars. The new plastic has other potential uses, including optical uses. "We've developed a new, simple and useful chemical process to convert sulfur into a useful plastic," lead researcher and UA professor Jeffrey Pyun said. Nextgeneration lithium-sulfur, or Li-S, batteries will be better for electric and hybrid cars and for military usesbecause they are more efficient, lighter and cheaper, said Pyun. Pyun and his colleagues tried something new: transforming liquid sulfur into a useful plastic that eventually could be produced easily on an industrial scale. Sulfur poses technical challenges. It doesn't easily form the stable long chains of molecules, known as polymers, needed make a moldable plastic, and most materials don't dissolve in sulfur. The scientists have named their process "inverse vulcanization" because it requires mostly sulfur with a small amount of an additive. Vulcanization is the chemical process that makes rubber more durable by adding a small amount of sulfur to rubber. Although some industrial uses for sulfur exist, the amount generated from refining fossil fuels far outstrips the need for the element. Some oil refineries, such as those in Ft. McMurray in Alberta, are accumulating yellow mountains of waste sulfur. "There's so much of it we don't know what to do with it," said Pyun. He calls the left-over sulfur "the garbage of transportation." About one-half pound of sulfur is left over for every 19 gallons of gasoline produced from fossil fuels, calculated coauthor Jared Griebel. The researchers have filed an international patent for their new chemical process and for the new polymeric electrode materials for Li-S batteries. Several companies have expressed interest in the new plastic and the new battery, Pyun said. FRENCH VINEYARD TO CAPTURE CARBON DIOXIDE EMISSIONS FOR MAKING TOOTHPASTE The owner of the Chateau Smith Haut Lafitte winery in Bordeaux, France has announced plans to capture carbon dioxide produced during the fermentation process to convert it into sodium bicarbonate. He will then sell this sodium bicarbonate to pharmaceutical companies for making toothpaste, as well as to various other industrial sectors. According to the Industrial Agricultural Products Center of the University of Nebraska, each gallon of wine produced is accompanied by production of 6.29 pounds of carbon dioxide. While the carbon dioxide produced during the fermentation process is minimal when compared to that generated from other related activities like packaging and transportation, it can still prove harmful to the environment and to human health. Carbon dioxide is heavier than air and does not dissipate easily. In 2008, two French wine makers suffocated due to carbon dioxide generated while treading grapes. n www.resourceworld.com 43

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