Solar cells are relatively inefficient at gathering the total range of sunlight’s spectrum that falls on them every day. Trying to find a way to capture more than a single wavelength or narrow band of the solar light, scientists at Massachusetts Institute of Technology (MIT) and at Peking University in China propose putting a strain on solar cells, creating a spatially varying bandgap that would react to more of the colors in light and thus give off more electricity. Changing the bandgap in a solar collector’s material enables excitation of electrons from not just visible light, but from energy sources such as infrared radiation. This has the potential to increase the cell’s energy output enormously since most of the sun’s radiation is in invisible form. Bandgap is a complex concept, and MIT provides a brief tutorial here. MIT’s news office reports: “’We’re trying to use elastic strains to produce unprecedented properties,’ says Ju Li, an MIT professor and corresponding …
Fixed Wings Find Their Way
Dynamic presentations by Sebastian Thrun and Nicholas Roy have alerted and informed CAFE Foundation’s Electric Aircraft Symposia attendees of highly sophisticated efforts to allow autonomous full-size automobiles and miniature helicopters to navigate through or over unfamiliar terrain. Using clues from lasers, infrared sensors, inertial guidance systems and sometimes GPS coordinates, the vehicles use control algorithms to guide themselves around obstacle-strewn courses. As noted in Science Daily and the The Massachusetts Institute of Technology’s press office this week, “Dozens of research teams have competed in a series of autonomous-helicopter challenges posed by the Association for Unmanned Vehicle Systems International (AUVSI); progress has been so rapid that the last two challenges have involved indoor navigation without the use of GPS.” Mini-copters have shown an amazing ability to not only navigate, but to perform complex tasks in swarms, such as building large architectural assemblies – all without human intervention (other than, one assumes, someone pushing a “go” button). MIT’s Robust Robotics Group has …
The Artificial Leaf
Daniel Nocera, Henry Dreyfus Professor of Energy and professor of chemistry at Massachusetts Institute of Technology (MIT), has caused a stir in the scientific community and attracted press attention including a recent feature article in the May 14 New Yorker. MIT’s own press release makes it sound all too simple and immediately appealing. “The artificial leaf — a silicon solar cell with different catalytic materials bonded onto its two sides — needs no external wires or control circuits to operate. Simply placed in a container of water and exposed to sunlight, it quickly begins to generate streams of bubbles: oxygen bubbles from one side and hydrogen bubbles from the other. If placed in a container that has a barrier to separate the two sides, the two streams of bubbles can be collected and stored, and used later to deliver power: for example, by feeding them into a fuel cell that combines them once again into water while delivering an electric …
MIT Solar Findings Mirror Those of 13 Year Old’s Tree Research
A recent report from MIT, replete with computer algorithms and graduate level insights, made your editor dip back into a story about a young naturalist who saw a model in nature that could lead to more efficient solar arrays. Both produced works of genius and give us hope for some real breakthroughs in solar power deployment. The Massachusetts Institute of Technology announced that, “Innovative 3-D designs from an MIT team can more than double the solar power generated from a given area,” and suggested that models of their new approach, “show power output ranging from double to more than 20 times that of fixed flat panels with the same base area.” Jeffrey Grossman, the Carl Richard Soderberg Career Development Associate Professor of Power Engineering at MIT and leader of the research team, reports in a paper published in the journal Energy and Environmental Science that the greatest improvements came in “locations far from the equator, in winter months and on cloudier …
Dipping and Coating for Better Batteries
Could dipping electrodes in a secret sauce improve supercapacitor and battery endurance and power? Could coating cell internals be the flavor of the month? These recipes for better batteries may improve things at a better than normal rate, if California researchers have anything to say about it. Working with his compatriot Dr. Jaephil Cho in South Korean, Dr. Cui of Stanford University has been a leader in developing improved battery technology, even developing a painted paper battery. In an appearance at the 2009 Electric Aircraft Symposium, Cui explained a basic truth of battery development – that improvements generally created about eight percent greater power or endurance in cells every year, leading to a doubling of battery capabilities every seven and one-half years. He aims to improve that rate of change in batteries and ultracapacitors. Although ultracapacitors are able to charge and discharge rapidly, they are only about one-tenth as energy dense as batteries of equivalent mass. Cui and colleague Zhenan Bao …
Cambridge Crude and Range Euphoria
Massachusetts Institute of Technology (MIT) scientists have announced what they claim is a “Significant advance in battery architecture [that] could be breakthrough for electric vehicles and grid storage.” According to a story by David L. Chandler from the MIT News Office, the new battery system is lightweight and inexpensive, and could make recharging “as quick and easy as pumping gas into a conventional car.” Seemingly requiring some active components within the battery, this “semi-solid flow cell” pumps solid particles suspended in a carrier liquid which form the cathodes and anodes through the system. According to the MIT news item, “These two different suspensions are pumped through systems separated by a filter, such as a thin porous membrane.” Mechanically more complex than today’s batteries, the system still has a claimed “10-fold improvement over present liquid-flow batteries” (not necessarily that much better than lithium ion, then), but lower manufacturing costs. The different fluids are contained in two different containers and not …
Aircraft That Don’t Ask For Directions
During the last two Electric Aircraft Symposia, Sebastian Thrun has shared his visions of future autonomous highways travelled by free-range cars that literally think ahead of the curve and don’t allow themselves to be boxed in – and even more daunting – autonomous helicopters that independently perform maneuvers that stretch the envelope in new directions and dimensions. His 2009 EAS presentation featured a Defense Advanced Research Projects Agency (DARPA) desert race in which his Stanford University team fielded a Volkswagen Taureg in a 132-mile race through the Mojave. Although not the ultimate winner, Stanford’s entry completed the course in a time that would have done pride to any human Baja race driver. More related to daily driving and eventual incorporation into a “smart” air traffic control system, Stanford’s entry in the DARPA Urban Challenge showed what is possible in close-quarter driving. As Thrun noted, careful measurements from aerial and satellite photographs show huge gaps in what is considered “bumper-to-bumper” traffic, with …
The Light at the End of the Funnel
In some exciting news that could make several quantum leaps in solar cell performance, Massachusetts Institute of Technology researchers have announced a hundred-fold increase in light gathering capabilities for solar cells. If a cell were able to exploit this increase, an aircraft such as the Solar Impulse could fly on 120 solar cells instead of the 12,000 now spread across its over 200-foot wingspan. We’ve reported on carpet-like light-capturing formats for increasing solar cell output, but the MIT approach funnels light down a multi-carbon nanotube filament, boosting the output of the “tiny” solar cell at the bottom. MIT’s press release explains the outcome. “’Instead of having your whole roof be a photovoltaic cell, you could have little spots that were tiny photovoltaic cells, with antennas that would drive photons into them,’ says Michael Strano, the Charles and Hilda Roddey Associate Professor of Chemical Engineering and leader of the research team. “Strano and his students describe their new carbon nanotube antenna, …
The Poop on the Puffin
Under normal circumstances, this editor would never resort to scatological titles, but Mark Moore, the NASA aerospace engineer behind this fantastic flying creation calls his electric craft, “Puffin” because, according to Moore, the bird after which it is named, “Hides its poop, and we’re environmentally friendly because we essentially have no emissions.” Like the Puffin, this craft looks a bit chubby and incapable of flight on the ground, but folds its legs on liftoff, and becomes a streamlined bullet. Moore, who spoke at last year’s Third Annual Electric Aircraft Symposium, and will return for this year’s CAFE Foundation gathering at NASA Ames Research Center in April, unveiled this concept at this year’s American Helicopter Society meeting in San Francisco. Moore and his colleagues, who include personnel at NASA, Massachusetts Institute of Technology, Georgia Institutute of Technology, the National Institute of Aerospace, and M-DOT Aerospace, plan on flying a third-scale model of the VTOL craft in March, and thus Moore may …
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