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Autor Tema: Energías Renovables  (Leído 48467 veces)


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Re:Energías Renovables
« Respuesta #600 en: Junio 22, 2012, 14:11:42 pm »

Nuevas células fotovoltaicas que son capaces de aprovechar el infrarrojo.

All-carbon solar cell harnesses infrared light

New type of photovoltaic device harnesses heat radiation that most solar cells ignore.

About 40 percent of the solar energy reaching Earth’s surface lies in the near-infrared region of the spectrum — energy that conventional silicon-based solar cells are unable to harness. But a new kind of all-carbon solar cell developed by MIT researchers could tap into that unused energy, opening up the possibility of combination solar cells — incorporating both traditional silicon-based cells and the new all-carbon cells — that could make use of almost the entire range of sunlight’s energy.

“It’s a fundamentally new kind of photovoltaic cell,” says Michael Strano, the Charles and Hilda Roddey Professor of Chemical Engineering at MIT and senior author of a paper describing the new device that was published this week in the journal Advanced Materials.

The new cell is made of two exotic forms of carbon: carbon nanotubes and C60, otherwise known as buckyballs. “This is the first all-carbon photovoltaic cell,” Strano says — a feat made possible by new developments in the large-scale production of purified carbon nanotubes. “It has only been within the last few years or so that it has been possible to hand someone a vial of just one type of carbon nanotube,” he says. In order for the new solar cells to work, the nanotubes have to be very pure, and of a uniform type: single-walled, and all of just one of nanotubes’ two possible symmetrical configurations.

Other groups have made photovoltaic (PV) cells using carbon nanotubes, but only by using a layer of polymer to hold the nanotubes in position and collect the electrons knocked loose when they absorb sunlight. But that combination adds extra steps to the production process, and requires extra coatings to prevent degradation with exposure to air. The new all-carbon PV cell appears to be stable in air, Strano says.

The carbon-based cell is most effective at capturing sunlight in the near-infrared region. Because the material is transparent to visible light, such cells could be overlaid on conventional solar cells, creating a tandem device that could harness most of the energy of sunlight. The carbon cells will need refining, Strano and his colleagues say: So far, the early proof-of-concept devices have an energy-conversion efficiency of only about 0.1 percent.

But while the system requires further research and fine-tuning, “we are very much on the path to making very high efficiency near-infrared solar cells,” says Rishabh Jain, a graduate student who was lead author of the paper.

Because the new system uses layers of nanoscale materials, producing the cells would require relatively small amounts of highly purified carbon, and the resulting cells would be very lightweight, the team says. “One of the really nice things about carbon nanotubes is that their light absorption is very high, so you don’t need a lot of material to absorb a lot of light,” Jain says.

Typically, when a new solar-cell material is studied, there are large inefficiencies, which researchers gradually find ways to reduce. In this case, postdoc and co-author Kevin Tvrdy says, some of these sources of inefficiency have already been identified and addressed: For instance, scientists already know that heterogeneous mixtures of carbon nanotubes are much less efficient than homogeneous formulations, and material that contains a mix of single-walled and multiwalled nanotubes are so much less efficient that sometimes they don’t work at all, he says.

“It’s pretty clear to us the kinds of things that need to happen to increase the efficiency,” Jain says. One area the MIT researchers are now exploring is more precise control over the exact shape and thickness of the layers of material they produce, he says.

The team hopes that other researchers will join the search for ways to improve their system, Jain says. “It’s very much a model system,” he says, “and other groups will help to increase the efficiency.”

But Strano points out that since the near-infrared part of the solar spectrum is currently entirely unused by typical solar cells, even a low-efficiency cell that works in that region could be worthwhile as long as its cost is low. “If you could harness even a portion of the near-infrared spectrum, it adds value,” he says.

Strano adds that one of the paper’s anonymous peer reviewers commented that the achievement of an infrared-absorbing carbon-based photovoltaic cell without polymer layers is the realization of “a dream for the field.”

Michael Arnold, an assistant professor of materials science and engineering at the University of Wisconsin at Madison who was not involved in this research, says, “Carbon nanotubes offer tantalizing possibilities for increasing the efficiency of solar cells and are kind of like photovoltaic polymers on steroids.” This work, he says, “is exciting because it demonstrates photovoltaic power conversion using an active layer that is entirely made from carbon.” He adds, “This seems like a very promising direction that will eventually allow for nanotubes’ promise to be more fully harnessed.”

The work also involved MIT graduate students Rachel Howden, Steven Shimizu and Andrew Hilmer; postdoc Thomas McNicholas; and professor of chemical engineering Karen Gleason. It was supported by the Italian company Eni through the MIT Energy Initiative, as well as the National Science Foundation and the De


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Re:Energías Renovables
« Respuesta #601 en: Junio 23, 2012, 23:08:59 pm »
Trina Solar realiza instalación de energía solar sobre tejado en la sede del equipo Lotus de F1


Trina Solar Limited, fabricante e instalador de material solar fotovoltaico, recientemente ha finalizado la instalación de una granja solar sobre cubierta en la sede del equipo Lotus de Formula 1 en Enstone (Oxfordshire, Inglaterra), en un nuevo centro de simulación que está equipado con tecnología de vanguardia que permite al equipo reproducir las condiciones de conducción, a extremos prácticamente reales, a efectos de investigar y optimizar los coches, sin necesidad de poner ningún vehículo en circulación, lo que también reduce costes y emisiones contaminantes.

El sistema solar fotovoltaico que suministrará electricidad verde al nuevo simulador del equipo, ha utilizado la nueva y rápida solución de montaje, Trinamount de Trina Solar, y se ha realizado en el tiempo récord de 2 días cuando con un sistema convencional se hubieran necesitado al menos de 5.

Esta huerta solar tiene la capacidad de suministrar 33.000 kWh de electricidad limpia al año, cantidad capaz de cubrir las tres cuartas partes de la energía que requiere el simulador para su funcionamiento, lo que disminuirá considerablemente la huella de carbono del equipo.

Según Patrick Louis, CEO del Equipo Lotus de F1, “la instalación del sistema solar fotovoltaico de Trina Solar refleja nuestro firme compromiso con las energías renovables. Esta instalación fotovoltaica genera la energía alternativa que más se adecua a nuestro entorno. El equipo Lotus F1 está comprometido con la promoción y el apoyo a iniciativas que aseguren que nuestras actividades contribuyen a un futuro más sostenible para nuestra sociedad”.

Magnífica iniciativa, aunque es una pena que una actividad con tanto desarrollo tecnológico como la Formula 1, no esté enfocada más a conseguir la eficiencia energética, a mejorar el ahorro en combustible y en materiales, etc, por ejemplo, promoviendo la investigación de compuestos en los neumáticos que duren incluso más de un gran premio, en vez de apostar por cambios de ruedas durante las carreras, para mejorar unas milésimas de segundo por vuelta. Cosa que es inapreciable para el que está viendo una carrera.

Se trataría de variar el enfoque de la competición, desde la reducción del tiempo por vuelta, sea al precio que sea, a tener más en cuenta la eficiencia, el ahorro, incluso el reciclaje y que todo esto sirviese como campo de prueba de tecnologías más sostenibles, que posteriormente utilizarían los vehículos de calle.

Aunque sean bienvenidas todas las inversiones verdes de este tipo, destinadas a generar la propia energía en el mismo lugar donde se va a consumir, a reducir los consumos, a evitar las pruebas reales, etc.


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