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Εμφάνιση αναρτήσεων με ετικέτα Research. Εμφάνιση όλων των αναρτήσεων

Κυριακή, 23 Δεκεμβρίου 2012

Αυτοκόλλητες ηλιακές κυψέλες για κάθε επιφάνεια

Ερευνητές από το Πανεπιστήμιο του Στάνφορντ ανακοίνωσαν ότι ανέπτυξαν μια αυτοκόλλητη ηλιακή κυψέλη που, σε αντίθεση με τις συμβατικές, μπορεί να τοποθετηθεί σε πολλών τύπων σκληρές επιφάνειες. Η εφεύρεσή τους, υποστηρίζουν, αυξάνει εντυπωσιακά τις δυνατότητες διείσδυσης της τεχνολογίας ηλιακής ενέργειας.
Υπό κανονικές συνθήκες, λεπτές «ταινίες» ηλιακών κυψελών τοποθετούνται σε εύκαμπτα υποστρώματα γυαλιού και πυριτίου, καθώς οι περισσότερες μη συμβατικές επιφάνειες δεν μπορούν να υποβληθούν στις θερμικές και χημικές διεργασίες που χρειάζονται για την παραγωγή των κυψελών.

Όπως εξηγούν οι ερευνητές στην έκθεσή τους, στην επιθεώρηση Nature Scientific Reports, η διαδικασία που επινόησαν ξεπερνά αυτό το εμπόδιο γιατί δεν προϋποθέτει την κατασκευή της ηλιακής κυψέλης πάνω στο τελικό επίστρωμα. Η μέθοδός τους, λένε, θα μπορούσε να οδηγήσει σε φθηνότερες, ελαφρύτερες, πιο εύκαμπτες κυψέλες.
Οι επιστήμονες παρομοιάζουν την κυψέλη τους με ένα... σάντουιτς, αποτελούμενο από μια πολύ λεπτή ταινία νικελίου, μια δεύτερη ταινία πυριτίου και διοξειδίου του πυριτίου και ένα προστατευτικό πολυμερές, τα οποία συνδέονται με μια θερμοευαίσθητη μεμβράνη. Όταν τοποθετηθούν σε νερό σε θερμοκρασία δωματίου, η ηλιακή κυψέλη αφαιρείται, σαν να ξεκολλάει, και μπορεί να τοποθετηθεί σε πάσης φύσεως επιφάνειες.

Ηλιακή κυψέλη τοποθετημένη πάνω σε επαγγελματική κάρτα.
Στόχος του Σιαολίν Ζενγκ και της ομάδας του ήταν να μεταφέρουν τα ενεργά υλικά της ηλιακής κυψέλης - αυτά που συλλέγουν το ηλιακό φως και παράγουν ηλεκτρική ενέργεια- από το σκληρό υπόστρωμα σε μια άλλη επιφάνεια, π.χ. ένα κομμάτι χαρτιού, πλαστικού ή ακόμη και στο πίσω μέρος ενός κινητού τηλεφώνου.
Όπως συμβαίνει με άλλες ηλιακές κυψέλες, καλώδια χρησιμοποιούνται για να μεταφέρουν την ηλεκτρική ενέργεια, όμως οι συγκεκριμένες μπορούν να τοποθετηθούν σε καμπύλες επιφάνειες. Επιπλέον, καθώς είναι ιδιαίτερα ελαφριές, εγκαθίστανται ευκολότερα σε σχέση με τα συμβατικά πάνελ.
Διαδικασία εφαρμογής αυτοκόλλητης ηλιακής κυψέλης. (Πηγή: Chi Hwan Lee, Stanford School of Engineering).
«Είναι σημαντικό το γεγονός ότι [με την τεχνική αυτή] δεν είχαμε καμία απώλεια αποδοτικότητας» σε σχέση με τις συμβατικές κυψέλες, προσθέτει ο Ζενγκ. Επόμενος στόχος της ομάδας του είναι να εφαρμόσει την ίδια τεχνική σε κυψέλες από ακόμη αποδοτικότερα υλικά. 
 .naftemporiki.gr
23/12/12
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  • Peel-and-Stick solar panels from Stanford engineering
For all their promise, solar cells have frustrated scientists in one crucial regard – most are rigid. They must be deployed in stiff, often heavy, fixed panels, limiting their applications. So researchers have been trying to get photovoltaics to loosen up. The ideal: flexible, decal-like solar panels that can be peeled off like band-aids and stuck to virtually any surface, from papers to window panes.
Now the ideal is real. Stanford researchers have succeeded in developing the world's first peel-and-stick thin-film solar cells. The breakthrough is described in a paper in the December 20th issue of Scientific Reports.
Unlike standard thin-film solar cells, the peel-and-stick version from Stanford does not require any direct fabrication on the final carrier substrate. This is a far more dramatic development than it may initially seem. All the challenges associated with putting solar cells on unconventional materials are avoided with the new process, vastly expanding the potential applications of solar technology.
Thin-film photovoltaic cells are traditionally fixed on rigid silicon and glass substrates, greatly limiting their uses, says Chi Hwan Lee, lead author of the paper and a PhD candidate in mechanical engineering. And while the development of thin-film solar cells promised to inject some flexibility into the technology, explains Xiaolin Zheng, a Stanford assistant professor of mechanical engineering and senior author of the paper, scientists found that use of alternative substrates was problematic in the extreme.
"Nonconventional or 'universal' substrates are difficult to use for photovoltaics because they typically have irregular surfaces and they don't do well with the thermal and chemical processing necessary to produce today's solar cells," Zheng observes. "We got around these problems by developing this peel-and-stick process, which gives thin-film solar cells flexibility and attachment potential we've never seen before, and also reduces their general cost and weight."
Utilizing the process, Zheng continues, researchers attached their solar cells to paper, plastic and window glass among other materials.
"It's significant that we didn't lose any of the original cell efficiency," Zheng said.
This shows demonstrations of the Stanford peel-and-stick thin-film solar process and various applications.
(Photo Credit: Chi Hwan Lee, Stanford School of Engineering.)
The new process involves a unique silicon, silicon dioxide and metal "sandwich." First, a 300-nanometer film of nickel (Ni) is deposited on a silicon/silicon dioxide (Si/SiO2) wafer. Thin-film solar cells are then deposited on the nickel layer utilizing standard fabrication techniques, and covered with a layer of protective polymer. A thermal release tape is then attached to the top of the thin-film solar cells to augment their transfer off of the production wafer and onto a new substrate.
The solar cell is now ready to peel from the wafer. To remove it, the wafer is submerged in water at room temperature and the edge of the thermal release tape is peeled back slightly, allowing water to seep into and penetrate between the nickel and silicon dioxide interface. The solar cell is thus freed from the hard substrate but still attached to the thermal release tape. Zheng and team then heat the tape and solar cell to 90°C for several seconds, then the cell can be applied to virtually any surface using double-sided tape or other adhesive. Finally, the thermal release tape is removed, leaving just the solar cell attached to the chosen substrate.
Tests have demonstrated that the peel-and-stick process reliably leaves the thin-film solar cells wholly intact and functional, Zheng said. "There's also no waste. The silicon wafer is typically undamaged and clean after removal of the solar cells, and can be reused."
While others have been successful in fabricating thin-film solar cells on flexible substrates before, those efforts have required modifications of existing processes or materials, noted Lee. "The main contribution of our work is we have done so without modifying any existing processes, facilities or materials, making them viable commercially. And we have demonstrated our process on a more diverse array of substrates than ever before," Lee said.
"Now you can put them on helmets, cell phones, convex windows, portable electronic devices, curved roofs, clothing – virtually anything," said Zheng.
Moreover, peel-and-stick technology isn't necessarily restricted to thin-film solar cells, Zheng said. The researchers believe the process can also be applied to thin-film electronics, including printed circuits and ultra thin transistors and LCDs.
"Obviously, a lot of new products – from 'smart' clothing to new aerospace systems – might be possible by combining both thin-film electronics and thin-film solar cells," observed Zheng. "And for that matter, we may be just at the beginning of this technology. The peel-and-stick qualities we're researching probably aren't restricted to Ni/SiO2. It's likely many other material interfaces demonstrate similar qualities, and they may have certain advantages for specific applications. We have a lot left to investigate."
This is a process developed for peel-and-stick thin-film solar cell from Stanford.
(Photo Credit: Chi Hwan Lee, Stanford School of Engineering)
 

Παρασκευή, 9 Νοεμβρίου 2012

Enhanced melting of Northern Greenland in a warm climate

Simulated ice thickness for the Greenland ice sheet for the last interglacial period (~126 thousand years before present). This was the most recent period with relatively warm temperatures at high northern latitudes, not unlike what is expected for the 21st century from projections of global warming. Circles show locations with ice core data.
 (Credit: Image courtesy of University of Bergen)

ScienceDaily (Nov. 9, 2012) — In a new study from the Bjerknes Centre for Climate Research, scientists show how the northern part of the Greenland ice sheet might be very vulnerable to a warming climate
The study is based on simulations with a state of the art global climate model and a dynamic ice sheet model of the last interglacial warm period. This period (~126 thousand years before present) is the most recent in Earth's history with temperatures warmer than present in the Arctic region, and has frequently been used as an analogue for a future greenhouse climate. During this period we know that the Greenland ice sheet was significantly reduced in size compared to today.


The model simulations show an extreme retreat of the northern part of the Greenland ice cap in response to the warm interglacial climate, a climate not unlike what we expect on Greenland in the very near future. This result is surprising, as temperatures on the north part of Greenland are colder than in the south. However, increased precipitation compensates for much of the increased melting of the southern part of the ice sheet in a warmer climate.
Today, most scientists expect that the southern part of the Greenland ice sheet is most vulnerable to a changing climate. In particular, there are several studies monitoring ice streams and fjord temperatures along the coast of southern Greenland. However, the new results indicate that the northern part of Greenland, at the fringe of the Arctic Ocean, should be particularly closely. In this area part of the ice sheet is grounded below sea level, and can respond rapidly once it starts receding.
If the Greenland ice sheet were to melt completely, it would result in an increase in mean global sea level by about 7 meters. However, the sea level impact of the observed recent accelerated melt of the ice sheet, as well as future projections of melt from the ice sheet, are not implemented by the current generation of climate models included in the IPCC effort.


Enhanced melting of Northern Greenland in a warm climate
9/11/12

Τετάρτη, 31 Οκτωβρίου 2012

Biofuel breakthrough: Quick cook method turns algae into oil



ScienceDaily (Oct. 31, 2012) — ANN ARBOR—It looks like Mother Nature was wasting her time with a multimillion-year process to produce crude oil. Michigan Engineering researchers can "pressure-cook" algae for as little as a minute and transform an unprecedented 65 percent of the green slime into biocrude.

"We're trying to mimic the process in nature that forms crude oil with marine organisms," said Phil Savage, an Arthur F. Thurnau professor and a professor of chemical engineering at the University of Michigan.
The findings will be presented Nov. 1 at the 2012 American Institute of Chemical Engineers Annual Meeting in Pittsburgh.
Savage's ocean-going organism of choice is the green marine micro-alga of the genus Nannochloropsis.
To make their one-minute biocrude, Savage and Julia Faeth, a doctoral student in Savage's lab, filled a steel pipe connector with 1.5 milliliters of wet algae, capped it and plunged it into 1,100-degree Fahrenheit sand. The small volume ensured that the algae was heated through, but with only a minute to warm up, the algae's temperature should have just grazed the 550-degree mark before the team pulled the reactor back out.
Previously, Savage and his team heated the algae for times ranging from 10 to 90 minutes. They saw their best results, with about half of the algae converted to biocrude, after treating it for 10 to 40 minutes at 570 degrees.
Why are the one-minute results so much better? Savage and Faeth won't be sure until they have done more experiments, but they have some ideas.
"My guess is that the reactions that produce biocrude are actually must faster than previously thought," Savage said.
Faeth suggests that the fast heating might boost the biocrude by keeping unwanted reactions at bay.
"For example, the biocrude might decompose into substances that dissolve in water, and the fast heating rates might discourage that reaction," Faeth said.
The team points out that shorter reaction times mean that the reactors don't have to be as large.
"By reducing the reactor volume, the cost of building a biocrude production plant also decreases," Faeth said, though both she and Savage cautioned that they couldn't say for sure whether the new method is faster and cheaper until the process is further developed.
Current commercial makers of algae-based fuel first dry the algae and then extract the natural oil. But at over $20 per gallon, this fuel is a long way from the gas pump.
"Companies know that that approach is not economical, so they are looking at approaches for using wet algae, as are we," Savage said.
One of the advantages of the wet method is that it doesn't just extract the existing fat from the algae—it also breaks down proteins and carbohydrates. The minute method did this so successfully that the oil contained about 90 percent of the energy in the original algae.
"That result is near the upper bound of what is possible," Savage said.
Before biocrude can be fed into the existing refinery system for petroleum, it needs pre-refining to get rid of the extra oxygen and nitrogen atoms that abound in living things. The Savage lab also is developing better methods for this leg of biofuel production, breaking the record with a biocrude that was 97 percent carbon and hydrogen earlier this year. A paper on this work is currently under review.
Once producing biofuel from algae is economical, researchers estimate that an area the size of New Mexico could provide enough oil to match current U.S. petroleum consumption. And, unlike corn produced for ethanol—which already accounts for half that area—the algae won't need to occupy good farmland, thriving in brackish ponds instead.
The research, "The Effects of Heating Rate and Reaction Time on Hydrothermal Liquefaction of Microalgae," was funded by the Emerging Frontiers in Research and Innovation program of the National Science Foundation. The university is pursuing patent protection for the intellectual property, and is seeking commercialization partners to help bring the technology to market.
Abstract: https://aiche.confex.com/aiche/2012/webprogram/Paper280193.html
Savage Lab: http://savageresearchlab.wordpress.com
EDITORS: Watch and link to a video about Savage's work on biofuels at http://www.youtube.com/watch?feature=player_embedded&v=dvGssEM4bLg#
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Biofuel breakthrough: Quick cook method turns algae into oil

Παρασκευή, 26 Οκτωβρίου 2012

Video: Grains Shape the Songs of Sand Dunes

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When plagued by whipping desert winds, sand dunes signal their displeasure with haunting moans that reverberate across the arid landscape. Some emit single-note songs while others mimic a jumbled chorus—but no one knew why they sang these different songs until now.
New research published online this week in Geophysical Research Letters finds that the size of sand grains shapes a dune's song.
 Scientists collected sand from a singing dune in Morocco that moans at around 105 hertz (Hz)—or, to a musician, that's G-sharp two octaves below middle C. They compared these notes to sounds from sand collected from a dune in Oman, which produces notes ranging from 90 Hz to 150 Hz (F-sharp to D). By creating mini-dune avalanches in the lab, scientists recreated these desert songs, finding that different layers of sand aren't necessary to produce the moans, as previous researchers contended. They also found that when they sieved the Omani sand so that the grains were similarly sized, the resulting "avalanche" produced a single-note song. The synchronized movement of sand grains, they conclude, produces the famed moaning, while grain size determines the notes contained in the song.
 .sciencemag.org
26/10/12

Οι νεκροί Έλληνες στα μακεδονικά χώματα σάς κοιτούν με οργή

«Παριστάνετε τα "καλά παιδιά" ελπίζοντας στη στήριξη του διεθνή παράγοντα για να παραμείνετε στην εξουσία», ήταν η κατηγορία πο...