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Self-Assembling Photovoltaic Cells 103

Posted by timothy
from the some-assembly-automatic dept.
dhj writes "MIT scientists have developed a self-assembling photovoltaic cell in a petri dish. Phospholipids (think cell membranes) form disks which act as the structural support for light responsive molecules. Carbon nanotubes help to align the disks and conduct electricity generated by the system with 40% efficiency. The assembly process is reversible using surfactants to break up the phospholipids. When filters are used to remove the surfactants the system reassembles with no loss of efficiency even over multiple assembly/disassembly cycles. The results were published September 5th in Nature Chemistry."
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Self-Assembling Photovoltaic Cells

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  • by Anonymous Coward on Sunday September 19, 2010 @08:25PM (#33631526)

    It seems to have added extraneous apostrophes in the process. Check your code. It's means "it is".

  • 40%! (Score:5, Informative)

    by ebonum (830686) on Sunday September 19, 2010 @08:36PM (#33631582)

    One of the problems with solar that no one seems to talk about is the system is limited by the size of the southern facing roof on a house. In the case of desert power generation, a large amount of land is required. If solar cells can make the leap from 12% efficiency to 40%, this will change everything. Your roof installation will be able to produce a much more meaningful amount of power especially in the context of trying to run air conditioning during day light hours. More importantly, the same applies for many malls, warehouses, factories, etc. At 12% efficiency, the roof of a mall is simply too small to generate enough power to be off the grid during the day. The amount of land required per MegaWatt will drop considerably. At 40% efficiency solar starts to become a much more viable option.

  • Re:40%! (Score:3, Informative)

    by DFJA (680282) on Sunday September 19, 2010 @08:51PM (#33631656)
    One thing that is worth remembering is that plants have an energy conversion efficiency of about 1%, if I remember correctly. So although 12% may seem low it is still a lot better than nature achieves. This is worth bearing in mind when you see fields of oil seed rape or other energy crops being grown - it would be far more efficient to cover the land area with photovoltaics. You could even grow sheep in the gaps between the panels.
  • Re:40%! (Score:5, Informative)

    by sunspot42 (455706) on Sunday September 19, 2010 @08:56PM (#33631684)

    Nobody needs to go "off the grid" for solar to become viable. It all comes down to $ per kw/h. Even if solar can only meet 10-20% of your needs, if you can recoup your investment in a reasonable timeframe, solar is viable.

    If you live in Phoenix and have a $200 a month light bill, a hypothetical $2,500 solar array that saves you just $40 a month but which lasts for 20 years looks like a pretty good deal - it'll pay for itself 3 times over. Unlike, say, a $2,500 3D television. And of course there's the network effect - if everybody installs one of the things, demand for electricity declines by 10-20% - as does the price - meaning you could all be saving a lot more than just $40 a month. That'll also spill over into the cost you pay for locally-produced goods and services.

  • Re:40%! (Score:5, Informative)

    by cheater512 (783349) <nick@nickstallman.net> on Sunday September 19, 2010 @09:09PM (#33631744) Homepage

    Actually photosynthesis tops out at 25% efficiency.
    11% using the sun's spectrum.

    It all depends on where you want to measure the efficiency.

  • Re:40%! (Score:4, Informative)

    by physburn (1095481) on Sunday September 19, 2010 @09:14PM (#33631770) Homepage Journal
    Don't know where you get the 12% number from. Sun Power solar cells are already 22% efficient, while the average commercial solar cells are 17 or 18% efficient.

    ---

    Solar Power [feeddistiller.com] Feed @ Feed Distiller [feeddistiller.com]

  • Re:40%! (Score:5, Informative)

    by Black Gold Alchemist (1747136) on Sunday September 19, 2010 @09:20PM (#33631800)
    FYI, at 20 percent efficiency in California, here's the math. One watt-peak = 2 kWh/year. One house = 11040 kWh /year, thus = 5520 watts peak.
    At 1 kW/m^2 (100 percent), you get 5.5 m^2, which means 2.3 meters (7.7 feet) on a side.
    At 40 percent, you get 13.7 m^2 = 3.7 meters (12 feet) on a side.
    At 20 percent you get 27.6 m^2 = 5.5 meters (17.23 feet) on a side.
    At 10 percent you get 55.2 m^2 = 7.4 (24.3 feet) meters on a side.
  • Re:40%! (Score:4, Informative)

    by JWSmythe (446288) <.jwsmythe. .at. .jwsmythe.com.> on Sunday September 19, 2010 @09:35PM (#33631850) Homepage Journal

        Actually, you hit on something that must be adjusted for solar to work. Modern structures are rarely insulated enough. That insulation can be natural (semi-subterranean homes), or artificial (like XPS, EPS, and fiberglass). On a few occasions, I've had opportunities to look inside residential walls. Rarely are the walls insulated well. They're insulated well enough to pass inspection, and meet the bare minimum of the building codes. For example, I was replacing the wall around a tub/shower. On the outside wall, there was only about 3/4" encapsulated fiberglass behind the concrete block wall. I guess that was enough to pass inspection at the time. The person who owns the house noted that in the summer, the A/C couldn't keep up. All you had to do was touch any of the interior walls. You could feel the outside heat on the exterior facing walls (from inside) and even the interior walls (not facing outside). The heat from the attic was heating the interior walls too.

        As long as it is acceptable to build houses as cheaply as possible, we will continue using more power than is required. So yes, solar can be way too expensive to supply even the power to just cool the house.

        There are some very interesting projects that people have done for alternative methods of cooling homes. While you may be able to hack something together from your local big-box hardware store, you'll never see a full kit nor instructions on doing it there. The building codes in your are may expressly forbid some. I know plenty of people who live in planned communities, where they are not allowed by deed restrictions, to put up solar panels, windmills, or even change the construction of their roof (a white roof reflects more solar energy than a black shingle roof).

  • Re:40%! (Score:3, Informative)

    by elashish14 (1302231) <profcalc4 @ g m ail.com> on Sunday September 19, 2010 @09:35PM (#33631852)

    Where are you getting this 12% efficiency factor from? That may be a decent figure for thin-film solar cells, but single-crystal silicon solar cells (the highest manufacturable efficiency) are well past 20% right now. And I don't believe the article at all when it says 40% power efficiency. Even the most advanced multijunction cells barely eek past 40% efficiency (and I think that's only due to the light being highly concentrated - >100x).

    What they probably meant is that the quantum efficiency is 40%, especially since it's impossible for any solar cell to exceed 86% within the detailed balance limit. 40% is nothing special compared to existing technology, though it's surprisingly high for a novel technology like this.

  • Re:40%! (Score:3, Informative)

    by sunspot42 (455706) on Monday September 20, 2010 @12:45AM (#33632782)

    Negative. You're assuming that if power use decreases by 10-20%, the cost of power will decrease. It will not. The power company will charge more for less.

    That's not true. The cost of power in many places in the US (and elsewhere, I'd imagine) varies during the course of the day depending on demand. So when demand is low power is cheap, but when demand is high (in the sunbelt, on hot sunny days), the price of power skyrockets, sometimes to ten times or more what it costs when demand is low.

    Solar cells have the unique property of generating maximum power just at the time when utility rates peak in the sunbelt. So looking at the average cost of power and comparing that to the cost of power generated by a solar cell doesn't begin to tell the whole story. Look at the peak cost of power and see how much of that a solar installation will shave off of your electric bill. And of course, thanks to the network effect, if everyone starts installing these things, the peak cost of electricity across the sunbelt will implode. Either way, consumers win. The power companies could try to jack up the cost a little, but they aren't going to be able to jack it up tenfold.

    Also, $200/mo light bill?! Maybe for AC in Phoenix... but that's a lot of lights. :)

    We were paying $200 a month in Phoenix to cool a 4 bedroom home 25 years ago. I'd imagine it's substantially more expensive today, especially when you factor in all the electronic, power sucking gizmos in the average home of 2010, from massive HD sets to power-guzzling desktop computers. My Core 2 box and its two LCD monitors consumes about 5 times as much electricity as my old Atari 800XL, 1050 disk drive and Amdek Color I monitor did back when I lived in Phoenix 25 years ago.

  • Re:40%! (Score:5, Informative)

    by zrbyte (1666979) on Monday September 20, 2010 @02:56AM (#33633168)

    40% is just the efficiency of the individual molecules in converting photons to electric charge. The overall efficiency of the device must be abysmal. The real breakthrough here lies in the fact that these guys can disassemble and reassemble the component light harvesting molecules of the device. This is important since photovoltaic devices using organic molecules are prone to degradation during irradiation by sunlight (see: http://en.wikipedia.org/wiki/Polymer_solar_cell [wikipedia.org]).

  • Re:40%! (Score:3, Informative)

    by Abstrackt (609015) on Monday September 20, 2010 @09:27AM (#33635426)

    Do you have any good links on this regard? I'm quite interested in this. I've been looking at (though not building yet) distillation refrigerators using solar heat as fuel.

    I'm not sure if this is exactly what you're looking for, but I've done a lot of research on building a passive house in a climate with extreme temperature variations and the following links made good starting points:

    http://en.wikipedia.org/wiki/Passive_solar_building_design [wikipedia.org]
    http://en.wikipedia.org/wiki/Superinsulation [wikipedia.org]
    http://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger [wikipedia.org]
    GreenBuildingTalk forums [greenbuildingtalk.com]

    Other options include designing the overhang of your house to be long enough to block most of the sun during the summer when it's higher but short enough to allow most of all of the sun through in the winter when it's lower, planting leafy trees with a lot of little branches near windows (the leaves block light during the summer and the small branches allow it through during the winter), and one that I cannot stress enough: the better your insulation is the more comfortable you'll be.

    In my current house the biggest change came from putting in triple-pane argon-filled windows. We could only afford to do half the house at a time and the half of the house with new windows was much more pleasant to be in both during the summer and the winter.

  • Re:40%! (Score:3, Informative)

    by Mindcontrolled (1388007) on Monday September 20, 2010 @09:33AM (#33635518)
    If you want to be real efficient, I guess you gotta take some clues from the usual "Passive House" [wikipedia.org] concepts. Now, passive house in it's original form is more geared towards temperate to cold climates, but the key element should be the same in a hot climate, namely controlling the ventilation in the house tightly and insulating as good as possible. Exchange humidity and heat between incoming and outgoing air using ERV [wikipedia.org], cool the incoming air in a second stage with an air-to-ground heat exchanger and in a third stage with a solar driven absorption heat pump [wikipedia.org]. Combine that with passive measures like painting the roof white or planting stuff on it, and providing ample shade for the sun side, and you should be set.

There is no royal road to geometry. -- Euclid

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