8 thoughts on “Monday message board

  1. Do you have to be consistent to be a greenie, or can you cherry pick the particular bits that suit you from time to time? Are true greenies really conservatives along the line of nature knows best? That means they’re against man made global warming, genetic modification of crops/plants and the similar genetic interference and manipulation of animals and particularly human beings. When in doubt, mother nature knows best and interference with Gaia’s natural laws will all end in tears, just like the externalities of climate change.


    Unique Quantum Effect Found in Silicon Nanocrystals Quantum Dot Materials May Improve Efficiency of Silicon Solar Cells

    Researchers at the US Department of Energy’s National Renewable Energy Laboratory (NREL), collaborating with Innovalight, Inc., have shown that a new and important effect called Multiple Exciton Generation (MEG) occurs efficiently in silicon nanocrystals. MEG results in the formation of more than one electron per absorbed photon.

    Silicon is the dominant semiconductor material used in present day solar cells, representing more than 93 percent of the photovoltaic cell market. Until this discovery, MEG had been reported over the past two years to occur only in nanocrystals (also called quantum dots) of semiconductor materials that are not presently used in commercial solar cells, and which contained environmentally harmful materials (such as lead). The new result opens the door to the potential application of MEG for greatly enhancing the conversion efficiency of solar cells based on silicon because more of the sun’s energy is converted to electricity. This is a key step toward making solar energy more cost-competitive with conventional power sources.

    An NREL team reported that silicon nanocrystals, or quantum dots, obtained from Innovalight can produce more than one electron from single photons of sunlight that have wavelengths less than 420 nm. When today’s photovoltaic solar cells absorb a photon of sunlight, about 50 percent of the incident energy is lost as heat. MEG provides a way to convert some of this energy lost as heat into additional electricity.

    The silicon nanocrystals produced by Innovalight, Inc., a thin-film solar cell developer, were studied at NREL as part of a collaboration between NREL and Innovalight scientists. The NREL team consisted of Matthew C. Beard, Kelly P. Knutsen, Joseph M. Luther, Qing Song, Wyatt Metzger, Randy J. Ellingson and Arthur J. Nozik.

    The findings represent an important extension of the range of semiconductor materials that exhibit MEG and are a further confirmation of pioneering work by Nozik, who in 1997 predicted that semiconductor quantum dots could exhibit efficient electron multiplication and hence increase the efficiency of solar cells.

    To date, all experiments showing the production of more than one electron per absorbed photon have been based on various types of optical spectroscopy. In a solar cell device it is necessary to extract the electrons produced in the quantum dots and pass them through an external circuit to generate electrical power. Such experiments are currently underway at NREL, Innovalight and other laboratories to demonstrate that MEG can indeed lead to enhanced solar cell efficiencies. Calculations at NREL by Mark Hanna and Nozik have shown that the maximum theoretical efficiency of quantum dot solar cells exhibiting optimal MEG is about 44 percent with normal unconcentrated sunlight and 68 percent with sunlight concentrated by a factor of 500 with special lenses or mirrors. Today’s conventional solar cells that produce one electron per photon have maximum efficiencies of 33 percent and 40 percent, respectively, under the same solar conditions.

    In addition to efficiently extracting the electrons from the quantum dots in solar cells, future research is directed toward producing MEG at wavelengths that have a greater overlap with the solar spectrum, as well as producing a much sharper onset of the MEG processes with decreasing wavelength of the photons.

    NREL is the US Department of Energy’s primary national laboratory for renewable energy and energy efficiency research and development. The NREL research was funded by DOE’s Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. NREL is operated for DOE by Midwest Research Institute and Battelle.

  3. StevieP,
    One involved an actual assault on a person and broadcast on national TV – the other was adults acting stupid but hurting no-one. One is much more serious than the other.

  4. Yes Andrew. By carefully (or even trivially) framing each event in a particular way, you can make them appear substantially different, to reflect your own biases and prejudices. That is the point that was being made in the story.

    One involved 2 idiots on an idiotic reality TV show behaving like obnoxious idiots.

    The other involved members of the Australian Defense Force, bringing shame and dishonour on themselves, their country, and the proud ANZAC tradition that they are a part of, actions that could only inflame already heavily strained cultural sensitivities. Their actions include broadcasting deplorable behaviour to an international audience.

    See, its easy.

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