Notas sobre Energías Renovables

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(Inglés) Microbios incrementan la eficiencia de captura de energía solar

Mensajepor Fermat » 03 Jun 2016 5:21 am

Microbe-linked solar panels are better than plants at converting sunlight to energy

Robert F. Service Jun. 2, 2016 , 2:00 PM


Plants are exceptional sunlight sponges. But they store only about 1% of the energy they soak up, locking it into the sugars and other organic molecules they use to build their cells. Scientists have boosted that number by a few percentage points with light-absorbing microbes and genetic engineering. But now, researchers have taken a more sizable jump with solar panels, creating a hybrid device that uses a combination of catalysts and microbes to convert 10% of the captured solar energy into liquid fuels and other commodity chemicals.

I’m a big fan of the work,” says Chris Chang, a chemical biologist and solar fuels expert at the University of California, Berkeley, who was not involved in the study. “It provides a really nice demonstration that you can get high efficiency [in solar chemical conversion], which is a key step.”

The new fuels could also solve another crucial problem: renewable energy storage. As solar and wind power grow in use, researchers have begun looking for ways to store the excess energy such systems produce. Batteries are too expensive for storing more than nominal amounts. But energy-rich chemicals, which can be piped around and kept in chemical tanks, could store much more at a manageable price.

The new work got its start in 2011, when researchers led by Dan Nocera, a chemist at Harvard University, created an artificial leaf that used energy from sunlight to split water into oxygen and hydrogen gas (H2). H2 can then be run through a device called a fuel cell to produce electricity. But because its energy density is so low—thanks to its vapor state—any fuel produced requires massive storage tanks or high pressures to compress it into smaller, more manageable volumes.

Several research teams followed up by combining the H2 with the carbon in carbon dioxide (CO2) to produce energy-dense liquid hydrocarbons. Last year, for example, Nocera’s group reported that it developed a hybrid system that used bacteria and electricity to “stitch” together H2—generated from splitting water—and the carbon from CO2 into a liquid alcohol called isopropanol. But the setup had a problem. The catalyst used to split water was made from a nickel alloy that generated a form of highly reactive oxygen that killed the bacteria. The only solution was to use an unusually high voltage of electricity, which produced fewer reactive oxygen molecules. It also sharply reduced the efficiency of converting the energy in the electricity to chemical bonds in the fuel. In the end, the system converted only 3.2% of the input energy into chemical fuel.

Now, Nocera and his colleagues have replaced the nickel catalyst with a new cobalt-phosphorous alloy version, which does not make reactive oxygen species. That allowed the team to lower the voltage, leading to a “dramatic increase in efficiency,” Nocera says. Their new hybrid setup can convert 10% of the energy in sunlight to a variety of chemicals and fuels, far above the efficiency of plants, they report today in Science.

As tantalizing as it seems to produce fuel merely from the starting ingredients of sunlight, water, and CO2 in the air, Nocera cautions that the solar fuel approach still has a long way to go before dethroning oil as the king of fuels. “It’s very hard to make this competitive with digging [oil] out of the ground,” Nocera says. Even so, he adds, solar fuel setups may one day help provide fuels and chemicals to the billions of people in developing countries who lack access because of poor infrastructure. His team is already taking a shot in India, where he is negotiating with researchers to pass along the intellectual property for the new method.

Última edición por Fermat el 13 Sep 2016 9:33 am, editado 1 vez en total.

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(Inglés) Producción de Energía Solar supera a la del Carbón el último mes en el Reino Unido

Mensajepor Fermat » 09 Jun 2016 6:04 am

Last month, for the first time ever, the UK generated more energy from solar than coal

By Dyllan Furness — June 8, 2016

The United Kingdom just passed a huge milestone in its renewable energy program – in May, for the first-ever calendar month, the UK generated more solar power than coal power. The difference wasn’t slight either. In fact, about 1,336 gigawatt hours (GWh) of electricity came from solar compared to the 893GWh generated by coal, according to research by analysts at Carbon Brief. That means a renewable source created over 50 percent more of the country’s power than coal.

The May milestones was preceded by a month earlier when, on April 9, UK solar energy plants produced more energy in a single day than their coal-based counterparts.

Each of these milestones is facilitated by an increase in solar energy capacity in the UK, according to Carbon Brief, but a steady collapse in coal energy (which has been falling since 2012) has proven to be a more immediate factor. Last year, coal energy generation fell to it’s lowest point in 55 years. However, coal still managed to make up 10 percent of the country’s electricity supply throughout the year.
And the UK isn’t alone in it’s sustainable energy milestone.

Recently in Chile, solar energy production has been so efficient that the country’s infrastructure couldn’t keep up. Between January 1 and April 30, the South American country had 113 days in which it essentially gave away electricity for free. Matters were worse (or better) in Germany last month when clear skies and strong winds generated so much renewable energy that the price of power dipped into the negatives. That same month, Portugal ran on renewable energy for four days straight. Across the pond, Denmark generated 42 percent of its electricity in 2015 from wind turbines.

The UK isn’t there quite yet, and it’s millstones are mostly symbolic, according to Carbon Brief, but the country’s recent achievements are promising.


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Nuevo dispositivo mejora la eficiencia de la energía solar térmica

Mensajepor Fermat » 16 Jun 2016 6:00 am

Nuevo dispositivo mejora la eficiencia de la energía solar térmica
15 Junio 2016, 19:51

Un equipo de investigadores del Instituto Tecnológico de Massachusetts (MIT) y el Instituto Masdar de Ciencia y Tecnología ha descubierto un método para incrementar de manera significativa la cantidad de luz solar que se puede absorber en las plantas solares térmicas para convertirla en energía.

"Nuestro equipo de investigación ha desarrollado una técnica de fabricación sencilla y rentable para crear dispositivos de absorción que pueden aprovechar una parte mayor del espectro solar, lo que aumenta su eficiencia, al mismo tiempo que mantiene bajos los niveles de emisiones", asegura el Dr. Tiejun Zhang del Instituto Masdar.

El nuevo sistema tiene la capacidad de convertir la energía solar de una manera más eficiente y a un coste más bajo, lo que ayudará a que las tecnologías sostenibles que se basan en el calor del sol sean más asequibles y produzcan más energía.

La novedosa técnica que ha diseñado el equipo consiste en el modelado de los dispositivos de absorción solar con pequeños orificios con diámetros inferiores a los 400 nanómetros distribuidos a intervalos regulares. Estas pequeñas incisiones penetran todo el dispositivo, lo que permite mejorar la gama de energía solar que puede ser absorbida. Gracias a este nuevo método se pueden aprovechar el 90% de todas las longitudes de onda que alcanzan la superficie de la Tierra.

Además, a diferencia de los absorbedores solares tradicionales, el nuevo diseño requiere muy poco material para su fabricación y se compone de solo dos capas: una película semiconductora y una capa metálica reflectante, que tiene un espesor total de 170 nanómetros.

"Esta idea se puede aplicar a la mayoría de los absorbedores solares convencionales", explica Jin You Lu, uno de los autores principales del estudio. "Con este patrón único, los amortiguadores se pueden aumentar para cosechar más energía solar a partir de las regiones ultravioleta y visible del espectro electromagnético".

El equipo está ahora trabajando en la optimización del sistema mediante la utilización de materiales alternativos para la capa metálica reflectante, como el aluminio, el cobre o la plata, lo que permitirá reducir todavía más el coste de los dispositivos de absorción.

Fuente y video:

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Floating solar is a win-win energy solution for drought-stricken US lakes

Mensajepor Fermat » 01 Jul 2016 6:14 am


Construction of Europe s largest floating solar panel array on London’s Queen Elizabeth II reservoir.

The Colorado River’s two great reservoirs, Lake Mead and Lake Powell, are in retreat. Multi-year droughts and chronic overuse have taken their toll, to be sure, but vast quantities of water are also lost to evaporation. What if the same scorching sun that causes so much of this water loss were harnessed for electric power?

Installing floating solar photovoltaic arrays, sometimes called “floatovoltaics,” on a portion of these two reservoirs in the southwestern United States could produce clean, renewable energy while shielding significant expanses of water from the hot desert sun.

The dual energy and environmental benefits of floating solar arrays are already beginning to earn the technology a place in the global clean energy marketplace, with floatovoltaic projects now being built in places as diverse as Australia, Brazil, China, England, India, Japan, South Korea, and California. And nowhere could they prove as effective as on lakes Mead and Powell, the two largest man-made reservoirs in the US.

The US Bureau of Reclamation estimates that 800,000 acre-feet of water (NB! cerca de 1000 millones m3) – nearly six percent of the Colorado River’s annual flow – is baked off Lake Mead’s surface by the searing desert sun during an average year. Lake Powell loses about 860,000 acre-feet annually to evaporation and bank seepage. Since floatovoltaics can reduce evaporation in dry climates by as much as 90%, covering portions of these two water bodies with solar panels could result in significant water savings.

Extrapolating from the spatial needs of floating solar farms already built or designed, the electricity gains from installing floatovoltaics on just a fraction of these man-made desert lakes could be momentous. If six percent of Lake Mead’s surface were devoted to solar power, the yield would be at least 3,400 megawatts of electric-generating capacity – substantially more than the Hoover Dam’s generating capacity of 2,074 megawatts.

This solar infusion could give the power-hungry Southwest a major boost in renewable electricity, and at least some of that power could piggyback on underused transmission lines built for the Hoover Dam.

A key selling point of floatovoltaics is the extra energy punch they deliver when compared to terrestrial photovoltaics in a similar climate. Hovering just above sun-shaded lake water, the floating photovoltaic panels would operate at cooler temperatures than solar arrays on desert land – a key factor in improving the productivity of semiconductors, including PV cells. One project proponent expects a 50% boost in electricity per watt of installed power from her company’s planned solar arrays at a sun-saturated sewage treatment pond in Jamestown, South Australia.
In Nevada, Arizona, and Utah, those who enjoy boating, fishing, snorkeling, and swimming on Lake Mead and Lake Powell may not immediately embrace the idea of solar arrays competing with their recreational activities. Yet with beaches retreating and marinas stranded on dry land, the benefits of curbing water loss are becoming increasingly clear. Moreover, at a time when some hydrology experts and conservationists are saying that Lake Powell should be partially drained to restore Glen Canyon and salvage Lake Mead, which is about 360 miles downriver, building solar power on a portion of these ailing artificial lakes may seem like a smarter alternative.

Japan has been a pioneer in floatovoltaics. It began modestly, floating enough panels on two reservoirs in Hyogo Prefecture to meet the electricity needs of roughly 920 households. Now it is scaling up. On a reservoir in Chiba Prefecture, a plant slated for completion in 2018 will generate power for nearly 5,000 households. In Japan’s relatively mild climate, preventing evaporation may be less critical than in the American Southwest. But the prospect of tapping solar power without taxing scarce land resources has its own merits in a small, densely populated country that is searching – post-Fukushima – for alternatives to nuclear power.

Floating solar arrays also are being installed on a reservoir in the Brazilian Amazon. About 910 sq miles of rainforest were flooded several decades ago when Brazil’s reigning military regime built the Balbina Dam, submerging millions of trees and destroying indigenous homes and hunting grounds. Today, due to persistent droughts and the languid flow of the river that feeds the Balbina Reservoir, the dam operates at only a fifth of its rated power capacity.

Soon, though, an expanding network of floating solar modules may help redeem this failed hydroelectric venture. In its pilot phase, a five-megawatt solar installation will cover an area equal to about five football fields and will generate enough power for roughly 9,000 households. Later, if all goes well, planners hope to build a massive 300-megawatt project that would produce enough electricity for about 540,000 Brazilian homes.

The list of pending or completed floatovoltaic projects goes on. In India, a pilot-scale installation has been successfully tested on a lake on the outskirts of Kolkata, and developers are negotiating for much larger floating solar plants on lakes in the state of Kerala. In California’s Sonoma County, sewage treatment ponds are now being equipped with floating PV arrays. And in the United Kingdom, Europe’s largest floating solar installation is nearing completion on the Queen Elizabeth II Reservoir outside London. Another is being built on a reservoir near Manchester. There, as in Japan, efficient use of available land resources is a key driver.

Though the US Southwest is far less land-constrained than the UK, the open desert is coming under increasing stress as solar developers seek suitable lands for their utility-scale projects. Protecting the desert tortoise has been a major concern at some sites, including two photovoltaic plants on Moapa Paiute tribal land in southeastern Nevada, just a few dozen miles from Lake Mead. In California, renewable energy advocates and conservationists have been at serious odds over the prospect of developing large solar sites in desert areas and adjacent lands in seven counties.

Floating solar arrays on reservoirs like Lake Mead and Lake Powell won’t supplant the need for land-based solar in California and other parts of the Southwest, but they can ease some of the pressure on fragile desert ecosystems.

As we confront the mounting impacts of global warming, maintaining a viable balance between water supply and demand in warmer climates will be especially challenging. In the sunny Southwest, reducing water losses to evaporation should be part of a wide-ranging water conservation strategy. Floating solar farms have a role to play, curbing water waste as they produce carbon-neutral power.

Fuente: ... n-us-lakes

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Re: Notas sobre Energías Renovables

Mensajepor Fermat » 08 Jul 2016 4:49 am

How solar energy can be transformed into fuel
Date:July 7, 2016

Ivo Alxneit, chemist at the Solar Technology Laboratory, Paul Scherrer Institute (PSI), preps for an experiment. Together with fellow researchers at the PSI and the ETH Zurich, he has developed a procedure that uses solar energy to produce fuel.

The sun is a clean and inexhaustible source of energy, with the potential to provide a sustainable answer to all future energy supply demands. There's just one outstanding problem: the sun doesn't always shine and its energy is hard to store. For the first time, researchers at the Paul Scherrer Institute PSI and the ETH Zurich have unveiled a chemical process that uses the sun's thermal energy to convert carbon dioxide and water directly into high-energy fuels: a procedure developed on the basis of a new material combination of cerium oxide and rhodium. This discovery marks a significant step towards the chemical storage of solar energy. The researchers published their findings in the research journal Energy and Environmental Science.

The sun's energy is already being harnessed in various ways: whilst photovoltaic cells convert sun light into electricity, solar thermal installations use the vast thermal energy of the sun for purposes such as heating fluids to a high temperature. Solar thermal power plants involve the large-scale implementation of this second method: using thousands of mirrors, the sun light is focused on a boiler in which steam is produced either directly or via a heat exchanger at temperatures exceeding 500 °C. Turbines then convert thermal energy into electricity.

Researchers at the Paul Scherrer Institute PSI and the ETH Zurich have collaborated to develop a ground-breaking alternative to this approach. The new procedure uses the sun's thermal energy to convert carbon dioxide and water directly into synthetic fuel.

"This allows solar energy to be stored in the form of chemical bonds," explains Ivo Alxneit, chemist at the PSI's Solar Technology Laboratory. "It's easier than storing electricity." The new approach is based on a similar principle to that used by solar power plants." Alxneit and his colleagues use heat in order to trigger certain chemical processes that only take place at very high temperatures above 1000 °C. Advances in solar technology will soon enable such temperatures to be achieved using sun light..

Producing fuel with solar heat

Alxneit's research is based on the principle of the thermo-chemical cycle, a term comprising both the cyclical process of chemical conversion and the heat energy required for it -- referred to by experts as thermal energy. Ten years ago, researchers had already demonstrated the possibility of converting low-energy substances such as water and the waste product carbon dioxide into energy-rich materials such as hydrogen and carbon monoxide.

This works in the presence of certain materials such as cerium oxide, a combination of the metal cerium with oxygen. When subjected to very high temperatures above 1500 °C, cerium oxide loses some oxygen atoms. At lower temperatures, this reduced material is keen to re-acquire oxygen atoms. If water and carbon dioxide molecules are directed over such an activated surface, they release oxygen atoms (chemical symbol: O). Water (H2O) is converted into hydrogen (H2), and carbon dioxide (CO2) turns into carbon monoxide (CO), whilst the cerium re-oxidizes itself in the process, establishing the preconditions for the cerium oxide cycle to begin all over again.

The hydrogen and carbon monoxide created in this process can be used to produce fuel: specifically, gaseous or fluid hydrocarbons such as methane, petrol and diesel. Such fuels may be used directly but can also be stored in tanks or fed into the natural gas grid.

One process instead of two

Up to now, this type of fuel production required a second, separate process: the so-called Fischer-Tropsch Synthesis, developed in 1925. The European research consortium SOLAR-JET recently proposed a combination of a thermo-chemical cycle and the Fischer-Tropsch procedure.

However, as Alxneit explains: "although this basically solves the storage problem, considerable technical effort is necessary to carry out a Fischer-Tropsch Synthesis." In addition to a solar installation, a second industrial-scale technical plant is required.

Direct production of solar fuel now possible

By developing a material that allows the direct production of fuel within one process, the new approach developed by Ivo Alxneit and his colleagues dispenses with the Fischer-Tropsch procedure and hence also with the second step. This was accomplished by adding small amounts of rhodium to the cerium oxide. Rhodium is a catalyst that enables certain chemical reactions. It has been known for some time that rhodium permits reactions with hydrogen, carbon monoxide and carbon dioxide.

"The catalyst is a pivotal research topic for the production of these solar fuels," says Alxneit. His PhD-candidate at the PSI Fangjian Lin emphasizes: "it was a huge challenge to control the extreme conditions necessary for these chemical reactions and develop a catalyst material capable of withstanding an activation process at 1500 °C." During the cooling process, for example, the extremely small rhodium islands on the material surface must not be allowed to disappear or increase in size since they are essential to the anticipated catalytic process. The resulting fuels are either used or stored and the cyclical process begins again once the cerium oxide is re-activated.

Using various standard methods of structure and gas analysis, researchers working in laboratories at the PSI and the ETH in Zurich examined the cerium-rhodium compound, explored how well the reduction of the cerium oxide works and how successful methane production was. "So far, our combined process only delivers small amounts of directly usable fuel," concludes Alxneit.. "But we have shown that our idea works and it's taken us from the realms of science fiction to reality."

Successful tests in high performance oven

During their experiments, researchers kept things simple by using a high performance oven at the ETH in place of solar energy. "In the test phase, the actual source of thermal energy is immaterial," explains Matthäus Rothensteiner, PhD-candidate at the PSI and the ETH Zurich whose area of responsibility included these tests.

Jeroen van Bokhoven, head of the PSI's Laboratory for Catalysis and Sustainable Chemistry and Professor for Heterogeneous Catalysis at the ETH Zurich adds: "These tests enabled us to gain valuable insights into the catalyst's long-term stability. Our high performance oven allowed us to carry out 59 cycles in quick succession. Our material has comfortably survived its first endurance test." Having shown that their procedure is feasible in principle, researchers can now devote themselves to its optimization.


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Re: Notas sobre Energías Renovables

Mensajepor Fermat » 21 Jul 2016 7:53 am

La energía osmótica, futura gran energía renovable?
Editado por Fanny Le Jeune | 20 julio 2016


Investigadores suizos han trabajado en el desarrollo de un nuevo método que utiliza agua dulce y agua salada para generar electricidad. La llamado energía osmótica ofrece un enorme potencial en términos de energía renovable.

Una energía en experimentación
Como concepto, la energía osmótica es bastante simple. El Instituto para la Transición Energética dedicada a energía marina renovable lo explica así:

"Energía osmótica es el nombre de la energía aprovechable a partir de la diferencia de salinidad entre agua de mar y agua dulce, en la que los dos tipos de agua están separados por una membrana semipermeable.

Ella consiste en el uso de la presión creada por la migración de las moléculas de agua a través de dicha membrana. La resultante de presión de agua asegura una velocidad de flujo que puede ser una turbina para producir electricidad. "

Usada mayormente en los estuarios, esta energía no es actualmente requerida en gran medida debido al bajo rendimiento encontrado en experimentos en todo el mundo. Una situación que podría cambiar rápidamente gracias al trabajo de investigadores de la Ecole Polytechnique Fédérale de Lausanne (EPFL), Suiza.

Un enorme potencial
El sistema desarrollado por este equipo presentó unos resultados de rendimiento jamás registrados antes, gracias a la creación de una membrana especial de tres átomos de espesor.

Los investigadores explican en página Nature que el éxito de su trabajo se debe en particular al material utilizado para la membrana, el disulfuro de molibdeno. Este material nanoporoso permite el paso a iones positivamente cargados, mientras que repele la mayoría de los iones con carga negativa.

Según los investigadores, por primera vez un material de dos dimensiones se utiliza para producir energía osmótica. "Tuvimos que fabricar y luego buscar el tamaño óptimo de los nanoporos," dice Jiandong Feng, quien dirigió la investigación, añadiendo: "Si (los nanoporos) son muy grandes, los iones negativos pueden pasar a través de ellos y la tensión será demasiado baja. Si son demasiado pequeños, no pasan suficientes iones y de nuevo la tensión va a ser demasiado baja. "

Según los investigadores, una membrana de un metro cuadrado cubierta al 30% de nanoporos podría generar 1 MW, frente a 5 W/m2 en la actualidad. La energía osmótica, a diferencia de sus otros primos renovables, no es intermitente, una característica que hace que sea una energía en la que podemos confiar sin temor. El único desafío restante son los medios para poner en práctica esta energía y aprovechar el enorme potencial que ofrece.


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Mejorando la producción de hidrógeno por energía solar (inglés)

Mensajepor Fermat » 28 Jul 2016 1:28 pm

Simple solution makes hydrogen production through solar water splitting more efficient and cheaper

13 July 2016 by Webredactie Communication

Researchers from Delft University of Technology (TU Delft), in collaboration with colleagues from the École Polytechnique Fédéral de Lausanne (EPFL), have found a simple yet very effective solution to greatly increase the efficiency and stability of hydrogen production through solar-driven water splitting. By separating the positive and the negative electrodes using a bipolar membrane, they were able to create local optimal conditions for electrolysis. Furthermore, they achieved this using only Earth-abundant catalysts and solar cells, opening the way for more efficient and stable water-splitting systems at lower cost. They have published their findings in the latest Advanced Energy Materials.

The thought driving Associate Professor dr. Wilson Smith in his research at TU Delft, is that one hours’ worth of sunlight reaching the Earth contains enough energy for one years’ worth of current energy demand worldwide. One of the challenges is being able to store and transport part of that energy for later use. So-called solar fuels could offer a solution, for example by harvesting solar energy and converting it into hydrogen by means of water splitting.


Electrolysis is the process involved, and in order to realize efficient and long term water splitting, having a strong acid around the negative cathode and a strong base around the positive anode would be best. Up until now, most of the commercially available electrolysers run in either a strong acid or a strong base electrolyte. In these systems, the highly corrosive environments limit the choice of catalysts, and they suffer from the constraint of finding a suitable pair of electrodes for the one electrolyte. So far only precious, and therefore expensive, metal catalysts can do that job.

Simple solution

The seemingly simple solution of separating the two electrodes by a specialized membrane, allows for optimization of the process, by offering the electrodes their respective best environments. It also means that Earth-abundant catalysts can be used in the process, making it cheaper, more efficient, and more stable.


Efficient process

The international research team, also including dr. David Vermaas from TU Delft, has shown that using a bipolar membrane in this manner can lead to a water splitting system efficiency of 12.7%. Natural photosynthetic processes in plants run at about 1% efficiency, while an efficiency of 10% is considered to be the starting point for potential commercial viability according to various techno economic analyses. An efficiency of 18% has been achieved for these types of processes, but only using precious metals and other very expensive (and unstable) materials. To be able to achieve this high efficiency while also using all Earth-abundant components in the solar cell and catalysts, makes the achievement an excellent demonstration for this technology. Smith: ‘This is a strong scientific step that can help the transition from lab scale systems into practical devices.’

Potential for other applications

The principle of separating the poles in these types of cells also looks very promising for other applications, according to Smith. ‘Using this bipolar membrane for electrochemical systems, we are now able in theory to click together the optimal half reaction components for processes like pieces of Lego. This has a huge potential for other electrochemical reactions such as the production of ammonia and hydrocarbons, while separating the oxidation half reaction completely. In this next step, we can finally replicate nature and make a truly artificial photosynthetic system that goes well beyond the efficiencies in nature.’
Última edición por Fermat el 11 Ago 2016 6:13 am, editado 1 vez en total.

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Re: Notas sobre Energías Renovables

Mensajepor Fermat » 11 Ago 2016 6:11 am

Una gran batería llena de aire
Por Luigi Jorio, Biasca
10 de agosto de, 2016 - 10:20

El viento produce electricidad incluso cuando la demanda de energía es baja (Keystone)

En un túnel bajo en los Alpes suizos, se está desarrollando un sistema innovador para almacenar energía eléctrica en forma de aire comprimido. Un proyecto único que podría dar un impulso decisivo a la energía renovable. Y reafirmar el papel de Suiza como una batería de Europa.

Almacenar el exceso de energía producida por las plantas solares y eólicas es uno de los principales retos de la transición a las energías renovables. El sol y el viento producen electricidad de forma irregular, de tal modo que hay una gran cantidad de energía en periodos de baja demanda. Como aprovecharla?

La respuesta de Giw Zanganeh, un ingeniero graduado de la ETH Zurich, se basa en el aire comprimido. Más precisamente en el almacenamiento de aire en galerías y espacios excavados en la montaña.

El principio es simple, dice el jefe de Alacaes, un proyecto financiado por la Oficina Federal de Energía. "El exceso de energía se utiliza para operar un compresor que bombea aire en el túnel. Cuando lo necesitamos, invertimos el flujo de aire comprimido y mueve una turbina que produce electricidad".

Ambiente submarino en la caverna

Para la planta piloto de Alacaes, que costó 4 millones de francos, se optó por un túnel en desuso al norte de Biasca, Ticino. Hasta hace pocos años, fue utilizado para transportar el material excavado el túnel ferroviario de base del Gotardo recientemente inaugurado.

"El túnel está en la condición que lo encontramos," dijo Giw Zanganeh, mientras nos guía en el interior. En su auto, avanzamos 700 metros en la oscuridad total antes de encontrar dos máquinas grandes. Estos son los compresores utilizados para bombear aire. "Son compresores especiales. Una nueva tecnología ", dice el ingeniero de origen iraní. Un poco más lejos, llegamos, a través de una puerta de acero, a la sala de almacenamiento de aire.

El espacio de almacenamiento de aire comprimido está cerrado por una pared de concreto de cinco metros de espesor, con una puerta de acero (

En este espacio a lo largo de unos cien metros, el aire se comprime a 33 bar. Para tener una idea, es la presión del agua de 300 metros de profundidad. Trabajar en condiciones extremas es una dificultad importante, señala Giw Zanganeh. Para supervisar la instalación, se utilizan cámaras especiales diseñadas para el trabajo bajo agua.

El propósito de esta fase es el estudio de la reacción de la roca a las altas presiones, probar su impermeabilidad y la eventual presencia de vibraciones. A diferencia de las instalaciones geotérmicas, el riesgo de causar un terremoto es prácticamente nulo, pues no se perfora la roca, dice el ingeniero.

Recuperar el calor

Las instalaciones de almacenamiento energético en forma de aire comprimido (tecnología CAES, “Compressed Air Energy Storage”) no son nuevas. La primera fue construida en 1978 en Alemania, y la segunda entro en operaciones en Estados Unidos a principios de los 90. Sin embargo, en comparación con estas dos, instaladas en minas de sal, el proyecto piloto de Biasca ofrece una mejor rendimiento dice Giw Zanganeh. "Esto gracias al calor de recuperación."

Cuando se comprime un gas, la temperatura aumenta. Este es un fenómeno físico. La temperatura puede llegar a 550 ° C, demasiado alta para ser “envasarla” de forma segura. En Alemania y Estados Unidos, el calor se disipa. Pero Giw Zanganeh - y esta es una de las innovaciones del proyecto Alacaes – ha diseñado un sistema para preservar esta energía y utilizarla para la electricidad en la fase de conversión de aire.
Gracias a la gestión de este calor, el proyecto de Biasca tiene un rendimiento del 72%, contra 45 a 50% de las instalaciones existentes, subraya el ingeniero. "Nos acercamos a la eficiencia de los sistemas de energía hidroeléctrica de acumulación por bombeo. Pero el sistema es menos costoso y más respetuoso del ambiente. No hay necesidad de mover el terreno para crear presas y embalses ".

Sistema prometedor a perfeccionar

"Además del bajo impacto ambiental, el uso de aire comprimido puede garantizar el suministro de grandes cantidades de energía durante un periodo prolongado. Un requisito cada vez más importante en el futuro ", dice Maurizio Barbato, profesor en el Instituto de la CIM para la innovación sostenible de la Universidad de Lugano.

Sin embargo, la tecnología, específicamente la del almacenamiento térmico, aún no está lista, dijo Maurizio Barbato, que sigue de cerca la experiencia de Biasca en el marco de un programa del Fondo de Investigaciones Científicas (PNR70) . El uso de la roca no garantiza una temperatura constante de aire en la salida, dijo. Ahora bien, esta es una condición indispensable para el buen funcionamiento de las turbinas. Los Institutos Tecnológicos Federales de Zúrich y Lausana (EPFL) están estudiando la manera de mejorar el sistema, por ejemplo mediante el uso de aleaciones metálicas.

Alacaes la tecnología es muy interesante, confirma Sophia Haussener, del Laboratorio de Ciencia e Ingeniería de Energías Renovables en la EPFL. "Sin embargo, el límite puede ser que la densidad de energía, relativamente baja: la cantidad de energía que puede ser almacenada por unidad de volumen es de 5 a 10 veces inferior a la de una batería recargable."

El consumo de Lugano, en un cubo

En Europa, especialmente en el norte, que produce más energía eólica, un sistema de aire comprimido puede tener un gran potencial. Idealmente, dice Maurizio Barbato, esta "gran batería" debe estar cerca de los parques eólicos. "Pero para aquellos de llanura, como al norte de Alemania, es complicado. Debe instalarse a cientos de metros de profundidad, o construir depósitos superficiales estancos, lo que sería muy caro. "Un país de montañas, cuevas y túneles como Suiza puede jugar un papel importante.

Pero Giw Zanganeh no cree mucho en las soluciones en túneles o antiguos búnkeres excavados en los Alpes. Los bunkers son generalmente muy pequeños y alargados, lo que no adecuado para minimizar las pérdidas. La forma ideal es el cubo o esfera, que tienen una relación de área / volumen menor. "Un cubo de 48 metros de lado almacenaría 500 MWh de energía. Es el consumo de la ciudad de Lugano (alrededor de 70.000 personas) durante 12 horas ", calcula el ingeniero.

Si las pruebas tienen éxito Alacaes, subraya Giw Zanganeh, Suiza podría reafirmar su papel de batería eléctrica de Europa. Y contribuir a la estabilización de la red europea, compensando las fluctuaciones de la energía eólica y solar en el continente.

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(Inglés) Científicos Hindúes crean árbol de paneles fotovoltaicos

Mensajepor Fermat » 30 Ago 2016 4:03 am

Indian Scientists Design Solar Tree to Save Space for Solar Power Generation

Indian scientists have designed a “solar tree” that they hope will help overcome one of the key challenges the country faces in the generation of solar power.

With photovoltaic panels placed at different levels on branches made of steel, “solar trees” could dramatically reduce the amount of land needed to develop solar parks.

“It takes about four-square meters of space to produce energy which otherwise would have required 400 square meters of space. So almost 100 times the space is saved, which as you know is very valuable,” said Daljit Singh Bedi, chief scientist at the Council of Scientific and Industrial Research (CSIR) in New Delhi, whose laboratory in Kolkata developed the tree.

A scarce resource in India, acquisition of land to develop roads, factories and other infrastructure is a sensitive issue that has led to frequent and sometimes violent protests from displaced people.

Scientists estimate the energy generated by a solar tree would be sufficient to light up five homes. They say the space-saving tree would not only make it easier to increase solar power generation to light up homes and streets in cities, but also in rural areas where farmers are unwilling to give up large tracts of land for solar panel installations.

The solar tree will also harness more energy compared to rooftop panels. “This design, it facilitates placement of solar panels in a way that they are exposed more towards sun and that way they are able to harness 10 to 15 per cent more energy, which is more or less equivalent to one hour more than the conventional format,” said Bedi.

India’s pledge to reduce its carbon emissions relies heavily on increasing the generation of solar energy. The world’s third largest emitter of greenhouse gases, India pledged at the United Nations Conference on Climate Change in Paris last year to slow the rate at which it emits greenhouse gases by one third over 2005 levels by 2030.

To achieve this, India has set an ambitious target of generating 40 percent of its total capacity from renewables by 2030 and reducing its reliance on polluting coal-based thermal energy. In the sun-drenched country, the main focus will be on solar power.

While the falling cost of photovoltaic panels in recent years has made solar power much more viable, and investment has been flowing into the growing sector, worries remain about acquiring large tracts of land to set up solar parks.

“It takes quite a bit of time which results in cost escalation and all those things,” said Amit Kumar at the Energy and Resources Institute, a research institute in New Delhi.

But will solar trees provide a sustainable option? Kumar cautions that innovations that aim at concentration of solar power so far have not made much headway.

“Unless we put those [trees] on a large scale, [only] then will we be able to get that answer,” he said.

However Indian officials like Bedi are optimistic.

“When we talk about plantation of trees, we would now talk about plantation of solar trees,” he said.

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Re: Notas sobre Energías Renovables

Mensajepor Fermat » 09 Sep 2016 7:53 am

Una solución eficaz y de bajo costo para el almacenamiento de energía solar


08/25/16 - ¿Cómo almacenar la energía solar? Transformándola en hidrógeno. Investigadores de la Escuela Politécnica Federal de Laussane (EPFL) y del Centro Suizo de Electrónica (CSEM) lo han logrado con células solares disponibles en el mercado y en un sistema sin materiales escasos. El resultado: un rendimiento, una estabilidad y una reducción de costos que jamás antes se ha alcanzado.

Cómo almacenar la energía solar para cuando el sol no brilla? Una solución prometedora es convertir esa energía en hidrógeno, por electrólisis de agua. Se trata de romper las moléculas de agua en hidrógeno y oxígeno, a través de la corriente producida por un panel fotovoltaico. El hidrógeno limpio, puede después almacenarse, para devolver electricidad a pedido, o usarse como combustible.

Pero no todo es tan simple. A pesar de los resultados de laboratorio prometedores en los últimos años, las técnicas de producción de hidrógeno son todavía muy inestables o muy caras para ser comercializadas a gran escala.

En EPFL y el CSEM, los investigadores eligieron combinar componentes ya probados en la industria para la fabricación de un sistema robusto y eficaz, lo que es el objeto del “Journal of the Electrochemical Society”. Su dispositivo supera los logros anteriores en cuanto a estabilidad, rendimiento y reducción de costos.

Su prototipo se compone de tres células solares de silicio cristalino de nueva generación, interconectados y conectados a un sistema de electrólisis sin materiales escasos. Se alcanzó una tasa de conversión de la energía solar en hidrógeno igual al 14,2%, habiendo funcionado el prototipo más de 100 horas.

Recorrer 10.000 km al año con un coche de hidrógeno
"Si instaláramos en Suiza entre 12 y 14m2 de estas células fotovoltaicas, sería posible almacenar suficiente hidrógeno para viajar 10.000 km anuales conduciendo un coche de pila de combustible de hidrógeno", señala Christophe Ballif, co-autor del estudio.

Este resultado no sólo constituye una eficiencia récord mundial con células solares de silicio, sino también un récord de producción de hidrógeno sin materiales raros. Sin contar con la gran estabilidad inherente del sistema.

La ventaja de las células de alta tensión
La receta para este rendimiento? La optimización de todos los componentes. Pero también en el uso de un tipo de células fotovoltaicas de silicio cristalino “híbridas", llamadas “de heterounión”, cuya estructura en sándwich con silicio cristalino y silicio amorfo proporciona un voltaje muy alto. Gracias a esta peculiaridad, es posible, mediante la conexión de sólo tres de estas células entre sí, generar una tensión óptima para generar la electrólisis. La parte electroquímica en sí, se lleva a cabo con un catalizador de níquel, un material abundante.

"Con las células de silicio cristalino tradicionales, hay que conectar cuatro células a la misma tensión, dijo Miguel Modestino, co-autor de la publicación. Esto es lo da ventaja a este dispositivo ".

Un método estable y económicamente viable
En términos de coste, rendimiento y durabilidad, el nuevo sistema es único. "Queríamos desarrollar un sistema eficiente y viable en las condiciones actuales, explica Jan-Willem Schüttauf, investigador de la CSEM y co-autor del estudio. Las células de heterounión que utilizamos son parte de la familia de las células de silicio cristalino, que por sí solo ya representa alrededor del 90% del mercado de los paneles fotovoltaicos. Se trata de una tecnología conocida y robusta cuya vida útil es superior a los 25 años. Además, también cubre la fachada sur del edificio CSEM en Neuchatel ", añade el investigador.

En la investigación que nos ocupa, los científicos utilizaron una heterounión celular estándar con el fin de probar su concepto. Utilizando la mejor de estas células, sería posible obtener un rendimiento por encima de 16%.


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