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Power Technology

Avalanche Effect Demonstrated In Solar Cells 234

esocid writes "Researchers at TU Delft (Netherlands) and the FOM (Foundation for Fundamental Research on Matter) have found irrefutable proof that the so-called avalanche effect by electrons occurs in specific semiconducting crystals of nanometer dimensions. This physical effect could pave the way for cheap, high-output solar cells. Solar cells currently have relatively low output, typically 15%, and high manufacturing costs. One possible improvement could derive from a new type of solar cell made of semiconducting nanocrystals and could theoretically lead to a maximum output of 44%, with the added benefit of reducing manufacturing costs. In conventional solar cells, one photon can release precisely one electron. However, in some semiconducting nanocrystals, one photon can release two or three electrons, hence the term 'avalanche effect.' This effect was first measured by researchers at the Los Alamos National Laboratories in 2004, and since then the scientific world had raised doubts about the value of these measurements. This current research does in fact demonstrate that the avalanche effect can occur."
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Avalanche Effect Demonstrated In Solar Cells

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  • Thermaldynamics? (Score:5, Interesting)

    by mlts ( 1038732 ) * on Tuesday May 27, 2008 @12:46AM (#23552083)
    Without violating thermaldynamic laws, I wonder how much electricity output this will add. I don't think it would double the current flow with 2-3 electrons popping out for each photon that strikes the array, but I know this should add a significant amount of efficiency.

    I just hope all these advances, especially ones that make solar cells cheaper to manufacture go into production. There are huge chunks of the world that are lifeless desert, and would be perfect for large solar and wind arrays, assuming one could find a way to transport the generated electricity to cities without too much current loss. Perhaps some chemical reaction that pulls carbon from the air directly to make ethane, then another reaction that converts the ethane to ethanol to be piped to places that can burn the ethanol for electricity. Yes, the chemical reactions to pull carbon from the air, and get it into ethanol are wasteful, but for very long distance transfer of energy (100-200+ miles), it would be less wasteful to do that, than to use standard power transmission lines. Even though the ethanol electricity generating plants would be adding carbon into the air, it would be carbon neutral due to the carbon being extracted at the solar/wind site.
  • Developing nations (Score:3, Interesting)

    by William Robinson ( 875390 ) on Tuesday May 27, 2008 @12:48AM (#23552093)
    This is great news, especially for developing nations whose energy demands are on rising trend. Countries like Indonesia, India and other middle east countries, where sun light is available in abundance, will benefit most.
  • by flyingfsck ( 986395 ) on Tuesday May 27, 2008 @01:11AM (#23552231)
    Using sunlight for electricity is not particularly attractive, but for the neat 'no moving parts' aspect. It is far better to use solar power for light, water and space heating - those remarkable innovations called windows and skylights for example.
  • by Cairnarvon ( 901868 ) on Tuesday May 27, 2008 @01:44AM (#23552459) Homepage
    A lot of governments give incentives for installing solar cells on your roof, and a lot of people *are* getting them installed as a result, so yes, there is a market, and a pretty big one at that. The fact that the US is lagging behind doesn't make that disappear.
  • by syphax ( 189065 ) on Tuesday May 27, 2008 @01:53AM (#23552507) Journal

    Efficiency matters, for a few reasons, including:

    1. Indirect costs (installation labor, racks, mounts, etc.) scale with the area of the array. The area of array required for a given power output goes with the inverse of efficiency. These costs are pretty significant, so efficiency has a direct impact on installed costs.

    2. There's lots of area available for solar panels, but solar energy is pretty diffuse, so you need a lot of area anyway. If a 1% efficient system cost a dime per watt installed, great, but you'd have to cover huge areas to generate significant amounts of electricity. There are practical limits. Even at 10-20% efficiency, you're still looking at large areas to generate a meaningful amount of juice.

  • by syphax ( 189065 ) on Tuesday May 27, 2008 @02:03AM (#23552551) Journal

    The numbers [] are all over the place and constantly coming down with new technologies, but you're looking at breakeven after 1-5 years or so.

    This is pretty good (EROEI is >> 1), and will continue to get better.
  • by TubeSteak ( 669689 ) on Tuesday May 27, 2008 @02:40AM (#23552719) Journal

    Using sunlight for electricity is not particularly attractive, but for the neat 'no moving parts' aspect. It is far better to use solar power for light, water and space heating - those remarkable innovations called windows and skylights for example.
    Tell that to the entire African Continent which has an abundance of sun & empty space, but a deficit of fresh water, power & air conditioning.

    I look forward to a future with solar powered desalination plants.
    It's a much brighter outlook than continent wide water wars forcefully giving everyone a skylight.
  • by somersault ( 912633 ) on Tuesday May 27, 2008 @03:52AM (#23553063) Homepage Journal
    Well, the company I work for is building a 1MW tidal turbine that is around 25 metres tall, not sure exactly how large the vent is, but to me that says that solar energy is pretty diffuse compared to the tides. Sunlight isn't that predictable during the day either unless you can get rid of all the clouds?
  • Re:Thermaldynamics? (Score:5, Interesting)

    by Yetihehe ( 971185 ) on Tuesday May 27, 2008 @04:33AM (#23553247)

    Perhaps some chemical reaction that pulls carbon from the air directly to make ethane, then another reaction that converts the ethane to ethanol to be piped to places that can burn the ethanol for electricity.
    Would methane be ok? If so, it is already done with CO2 and sunlight [].
  • by Obvius ( 779709 ) on Tuesday May 27, 2008 @05:06AM (#23553383)
    If I remember correctly from my old physics undergraduate days, the total available solar power across the entire spectrum is only just over 1kW per square metre at the Earth's surface. It's a useful thing to bear in mind when considering the viability of solar power. even with 100% efficient solar panels, we're unlikely ever to run a house on a single small panel.
  • Re:Thermaldynamics? (Score:3, Interesting)

    by mlts ( 1038732 ) * on Tuesday May 27, 2008 @05:24AM (#23553449)
    Methane works, but ethane is a lot easier on metal compounds (far less corrosive) and safer in general (although its still highly flammible). Drink ethanol (assuming not denatured), one gets drunk (or dies from alcohol poisoning). Drink methanol, and the optic nerve gets permanently polymerized by the by-products such as formic acid, which renders a person permanently blind.
  • by Anonymous Meoward ( 665631 ) on Tuesday May 27, 2008 @06:35AM (#23553833)
    We may not need something as drastic as a Manhattan Project. How about the Apollo program instead?

    When JFK pledged to put a man on the moon in 10 years, we did it -- even though the Cold War arguments re: national security were a bit hysterical.

    Why can't we have a leader pledge to reduce America's dependence on oil by 50% in 10 years? Sounds just as possible to me as Apollo XI would have in 1960. And it's obviously more practical.

  • Re:Max Power (Score:2, Interesting)

    by catprog ( 849688 ) on Tuesday May 27, 2008 @07:51AM (#23554199) Homepage
    Average of 5 hours a day = total power per square meter = 5Kw

    My house + 50% = 30kwh / day

    = 6 square meter

    30% efficiency

    Only about 20 square meters required.

  • by soren100 ( 63191 ) on Tuesday May 27, 2008 @08:14AM (#23554339)

    Right now, and for the last 20 years, wind and solar have been huge money-losers, and only exists BECAUSE of the massive subsidies. If we subsidized wind or solar at a level to get useful output levels, we'd spend literally trillions more per year.
    Nice try, troll. Countries like Denmark have had tremendous success [] with alternative energy sources such as wind power. Currently about 20% of the energy used in Denmark comes from wind power, and there is about a $5 billion market in exporting turbines. Currently over a third of the wind turbines used worldwide [] are built by Danish manufacturers such as Vestas.

    On windy days, Denmark actually generates "too much" power from wind (about 40%) so they are working on an electric car system [] to act as a "sink" to dump the excess energy. (currently the hydroelectric generating facilities in Norway and Sweden are used to smooth out the changes in energy production from wind)

    The wind power project has been such a success that Denmark is currently planning to double its offshore wind farms, after studies showed that it would not harm the environment. The current goal is to increase wind power to 30% of total output by 2025.

  • by Ihlosi ( 895663 ) on Tuesday May 27, 2008 @09:38AM (#23555159)
    Still doubt it could handle heating (excepting heat pump or geothermal).

    Don't forget _solar_ heating. That way, you can squeeze a bit more efficiency out of the space on your roof, plus it can be used to cool the solar cells, which improves their efficiency also.

  • by MrKaos ( 858439 ) on Tuesday May 27, 2008 @09:46AM (#23555271) Journal

    Or even better, instead of having massive plants with a huge footprint make use of smaller pup nuclear reactors - about the size used in a naval ship. One of those could be placed where the power substations are now and pick up the slack that the solar panels can't fulfill. They wouldn't present any real contamination danger as once their fuel was spent after 30 years or so you truck out the entire unit and refurbish (i.e. refuel) it under controlled conditions in a remote area - while in service the internals of the thing aren't opened up.
    Wouldn't it be better to you a more direct method of energy transfer by processing domestic waste products into energy. It's my understanding that this is already underway in London [], an example of where things can be done at an urban level. Some of the things already underway is recovery of waste heat, domestic waste and other micro-generation projects at an urban level. And more proposals [] are underway.

    Now effective solar panels and batteries to go with them would allow us to move to a more decentralized model.
    Why can't we just go ahead and do that now? It would have the same effect as bringing not only the energy closer to the consumer but the processes, whilst reducing the pressure on existing centralised infrastructure because when you think about it, generally, to heat our homes we convert heat to motion to electricity over wires to our homes and back into heat again. If our houses already produce a surplus of heat why can't we use something like water to move that heat around on a street or urban level to generate electricity locally?

    Why don't we just use our homes to munch up our waste products and convert them to gas to run fuel cells that make electricity or process the at an urban level for gasses and pass that waste product further - for example why can't we use sewage water with a lot of nutrients to soak up carbon from our underground freeways or power stations with algae and produce bio-diesel. Given that the process would have inefficiencies, but who cares - they were waste products anyway, and after the inefficiencies you rightly point out in the grid anyway how much energy do we throw away after we have used it?

  • Re:APDs (Score:4, Interesting)

    by bperkins ( 12056 ) on Tuesday May 27, 2008 @10:21AM (#23555769) Homepage Journal
    It's hard to say without seeing the article in Nano-letters, but based on the diagram and a vague description, I'd guess that it works something like this:

    A high energy electron hole pair is created by a photon, which then relaxes down to a lower energy state. But, instead of emitting a phonon (heat), it creates another electron hole pair, and you end up with two. I suppose this process could repeat itself, so that many different wavelengths would all produce energy with reasonable efficiency.

    This is in all likelihood facilitated by the complex energy band structure of the (essentially) polycrystalline semiconductor.

    I'm not so sure how directly applicable all of this is. I suspect that some theorist postulated that this could happen, but it was difficult to prove experimentally. It seems to me that the hard work of actually producing an workable device hasn't been done yet.

    From what I can tell, this work is done in PbSe, which I don't think is a suitible for huge volume production.

    But I could be wrong in all this.
  • by Doc Ruby ( 173196 ) on Tuesday May 27, 2008 @10:33AM (#23555965) Homepage Journal

    Published on 16 Jun 2006 by Energy Bulletin. [...] This review has concluded that the likely energy payback of a typical domestic sized rooftop grid connected PV cell is approximately four years.

    A domestic rooftop grid can receive something like 400W:m^2 (averaged across weather/seasons/night) here in NYC, generating 72W:m^2 (at the more likely 18% efficient PV). My building is 7.6x21.3m, 162m^2, or 11.655KW. We have 4 apartments, which consume (as the average household in NYC) about 2KW each. So we've got 3.65KW extra, or 31.4% surplus to sell back to the grid.

    NYC has an average 25850 people per Km^2, with an average household of 2 people. A square KM of PV could generate 72MW for those people's requirement of 26MW. Even if only 1/3 of the City's area were PV, we'd power ourselves completely. []

    If PV averaged 40% instead of the 18% I used in these figures, that's only 1/6 the area needed. If the City and state offered tax incentives per grid watt self-generated for 5 years (while those PVs paid back their manufacturing energy investment), most roofs would have them. Consider the extra savings from offloading from our blackout-prone Con Edison grid, and replacing blacktop roofs with something insulating, and NYC would probably show a net energy profit after less than 10 years. Which, like everything else in NYC, would be readily converted to actual monetary profit.
  • by dpilot ( 134227 ) on Tuesday May 27, 2008 @11:03AM (#23556395) Homepage Journal
    It doesn't require effort from millions of Americans.

    All you have to do is make more economical energy generally available. It's still a project with participation in the thousands or tens of thousands. Once a way to save money is readily available, the millions will do so.

    The hard part is when the way to save money is available, but not readily. In other words, when it's available, but you have to make substantial changes or investments in order to realize it. For instance, imagine photovoltaic panels with a 10 year payback vs either a 1 or 2 year payback, or some sort of "encouragement legislation" in place that turned the 10 year payback into a 1 or 2 year payback.
  • by somersault ( 912633 ) on Tuesday May 27, 2008 @12:31PM (#23557737) Homepage Journal
    Yep, here in Scotland it can get rather cloudy. In fact it's definitely more often cloudy than not.

    Wasn't trying to slag off solar power btw, just pointing out how 1kW per square metre is pretty diffuse at least by tidal standards, and probably by wind standards too. I think all forms of renewable energy are worth considering though, and things like solar and wind power tend to complement each other quite well, as when it's dark and stormy, it will probably also be quite windy.

    Do you get many tornadoes or sandstorms or anything like that in Arizona (guessing that's what AZ is :p )?

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