Ultraefficient Photovoltaics

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• 	How does this compare with nature? cakass on 06/15/2007 at 5:23 AM
  Posts: 1	How do these efficiencies compare with that of photosynthesis as a way of capturing solar energy? Rate this comment: (Reply)

• comparing nature ranadrew on 06/15/2007 at 11:05 AM

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  About 5% for the natural process analyzed in this interesting summary by Poles in Krakow: www.if.uj.edu.pl/Foton/92-special%20issue/pdf/06%20kburda.pdf However, beware statistics (numbers) can be misleading.  In comparisons to nature and her processes the devil is always in the details.  Cutting out a little piece of her and analyzing it in detail often leads to misinterpretations and underappreciation of her sublime design perfection. Rate this comment: (Reply)

• cellulosic biomass 0.1%; algae 1% to 20% ? efficient nekote on 06/15/2007 at 11:42 AM

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  According to a correspondence with Cornell U. Prof. David Pimental, cellulosic biomass captures only about 0.1% of the solar energy, per acre, per year. Algae are supposed to be 10 to 100+ times as efficient, per acre, per year - meaning 1% to 10% (sometimes to 200 - 20%) and there are numbers of projects active in that vein. If those PV % are close to correct, these 240 and 1,000 to 1 *CONCENTRATING* collectors would seem to have an advantage at ~ 40%.  (FWIW - sounds almost like the Solex device in the James Bond movie "The Man with a Golden Gun - 1974  :) ) The rub, as alway, is $/unit energy, delivered to the end consumers. Which method(s) will provide the lowest delivered cost KWH or gallon of liquid fuel, as paid for by consumers? Rate this comment: (Reply)

  • 	Re: cellulosic biomass 0.1%; algae 1% to 20% ? efficient mpalmer41 on 06/15/2007 at 5:03 PM
    Posts: 1	Do you have any references on the algae efficiency?  I would like to look them up. Rate this comment: (Reply)

  • Spectralab cells rhapsodyinglue on 06/16/2007 at 6:51 PM

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    I would say you can take this result to be accurate.  They have a long history of producing cells for satellites and the efficiency of the cells has been creeping up by a percent or few each iteration.  No out of blue claimed breakthrough... just consistent sound engineering over a lot of years. As for the expense... I guess at this point it isn't cost competitive with the other solar concentrating technology.  Recently there have been announcements of utility scale solar troughs and stirling dishes... with the largest commitment seeming to go to stirling dishes.  So I'd assume they have the current cost advantage. Given that these cells require concentrated sun there is the expense of some form of optics and a tracking mechanism.  One company is developing a very novel flat panel solar concentrator that may be a good match for these ultra efficient PV cells... http://www.solfocus.com/technology_gen2.html Rate this comment: (Reply)

    • Stirling dishes?  $/KWH to consumer nekote on 06/17/2007 at 11:23 AM

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      I haven't come across any stirling dish stories, recently.  Gotta' handful of URLs to share? Care to consider Green and Gold Energy's SunCube: http://www.greenandgoldenergy.com.au/ ? I'm not doubting the laboratory efficiency claims. But that % is always the very highest the efficiency can possibly be, for systems that use that style of device. Rather, there are so many other factors (focusing, tracking, reflection, DC to AC inverter, dirt / aging, transmission distance to market, ... efficiency losses, not to mention capital and operating costs, longevity, reliability, availability ...) that weigh heavily on the final, most relevant $/KWH price to consumers.  In essence the net PV %, so to speak. So, I should have said if those PV % are close to what the end user finally gets - meaning bare minimum losses elsewhere and bare minimum additional expenses. Rate this comment: (Reply)

      • Re: Stirling dishes?  $/KWH to consumer asdar on 07/06/2007 at 11:52 AM

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        There are two Stirling Energy Systems, stirling dish power fields that are waiting final permitting to begin construction. Approval for both projects have already been granted. http://www.energy.ca.gov/sitingcases/all_projects.html They're clear down at the bottom in the section for renewables. Final construction certification is supposed to be in Aug, for stirling one, and Sept for two. SES dish isn't as efficient as 40%, more like 20%, and has some operating expenses. I still like the tech, and think the biggest advantage is that it requires no exotic materials. Rate this comment: (Reply)

    • 	Re: Spectralab cells darkstar57 on 06/18/2007 at 7:41 AM
      Posts: 2	240 concentration of sunlight to a 40 % eff cell means 60 % of that energy has to go somewhere... like melt the cell? Rate this comment: (Reply)

      • 	Re: Spectralab cells pfairley on 06/18/2007 at 4:40 PM
        Posts: 5 Avg Rating:	Some of the 60% represents light that was not absorbed but some, as you suggest, represents light that is absorbed and converted to heat instead of electricity. Keeping the produced heat from melting the equipment, for example by ensuring air flow over the device, is an important component of the engineering of a solar concentrator system. Rate this comment: (Reply)

        • 	Re: Spectralab cells cscoxk on 06/19/2007 at 2:59 PM
          Posts: 1	Putting the solar cells on aluminium square pipes and cooling by circulating water enables much of the 60% heat to be harvested (or stored. If we can utilise 50% of the heat then we now harvest up to 70% of the energy falling on an area. This starts to change the economics. Rate this comment: (Reply)

          • 	Re: Spectralab cells OptiPes on 07/09/2007 at 8:10 PM
            Posts: 3	Yes, the necessity of cooling really changes economics of PV. I wonder, why TFA doesn't mention it... Rate this comment: (Reply)

      • 	Re: Spectralab cells CarlHitchon on 10/16/2007 at 1:41 AM
        Posts: 14 Avg Rating:	A common technique is to use very small cells with heat sinks that use radiational and convective cooling.  I would be nice to harvest the heat left after conversion for hot-water, dryer hot air, and heating. A possible limitation is that these cells have to be kept fairly cool or efficency degrades rapidly. Rate this comment: (Reply)

• 	upmost importance sacapiloa on 06/16/2007 at 1:56 PM
  Posts: 9 Avg Rating:	developing solar tech seems to me to be on of the greatest ways of saving the earth Rate this comment: (Reply)

  • 	Re: upmost importance r19578 on 06/16/2007 at 7:54 PM
    Posts: 1	So far nuclear still is the cleanest energy we have. If you calculate the entire life cycle polution including the process of making and recycling the panel, solar power is comparable to wind power, but far behind nuclear. Rate this comment: (Reply)

    • 	Re: upmost importance randman420 on 06/16/2007 at 10:32 PM
      Posts: 6 Avg Rating:	I don't see how you can say nuclear power is clean when we don't even have a place to put the waste products not to mention mining all the uranium. You have to mine a lot of uranium just to get a miniscule amount of plutonium and then you have to put all the work into refining it. That just doesn't sound all that clean compared to growing some crystals? Rate this comment: (Reply)

      • Re: Nuclear energy spectator on 06/18/2007 at 4:46 PM

        Posts: 1

        Nuclear power plants do not run on the Plutonium. They use enriched Uranium isotope, and Plutonium is a by-product formed during fission in the nuclear reactor. Looking generally, in the nature there is plenty of the radioactive elements, but they are almost evenly distributed all over. That makes intensity of the localized radiation to be below limit to which life has been genetically accommodated. Problem with radioactive waste are isotopes produced by nuclear reaction, which can be more radioactive than starting material. Now, if all this waste is evenly distributed over the earth, local radiation will be really negligible. But this is not at the moment possible. There are many other more dangerous materials, which human race is throwing around, but we do not recognize its dangers, because general public is not informed, or the facts are kept hidden by governments. Just to mention Chemical weapons (neurotoxins, neural toxic gases), like VX, which even US government has enclosed in the cement encased barrels and disposed huge amounts in the oceans. Just imagine, what can happen after several decades, when see water “eats” through these containers, and VX starts leaking under a see. Rate this comment: (Reply)

        • Re: Nuclear energy jdorgan on 07/06/2007 at 5:41 AM

          Posts: 1

          You are correct, sort of - nuclear plants in the USA run on refined uranium in a "once through" process. Laws intended to prevent proliferation restrict reprocessing, this adds to the waste problem bu tmore importantly it means that nuclear energy is NOT a long term solution. This is because there are finite quantities of uranium and once we burn through them and bury them, that game is over. With growing world energy demand and the present security considerations, we migth only have a 50 year supply of uranium. Note the run up in both prices and futures in recent years! If we do change our laws to allow reprocessing, there is a considerable (effectively infinite) energy supply. However, for each gigawatt-year of electricity generated (the size of a typical modern coal fired power plant is aroung a GW) you produce one ton of radioactive cesium and one ton of radioactive strontium - these materials have half lives of about 400 years. Is a sustainable energy system one that each year produces two tons of radioactive material that needs 400 year stewardship? Do you think stewardship for even a couple hundred years is possible to guarantee? I remind you that the USA, at 231 years old, is the longest standing government presently on the planet. We have a perfectly beautiful nuclear reactor, one that uses clean fusion power and which is safely located 92 million miles from earth - why not use it? Rate this comment: (Reply)

          • 	Re: Nuclear energy ryanweed on 08/20/2007 at 10:50 AM
            Posts: 1	We also have fusion energy on earth. The ITER experiment, the largest scientific collaboration ever, is a fusion reactor being built in Cadarache , France. Rate this comment: (Reply)

    • 	Re: upmost importance YogaMan on 06/27/2007 at 6:41 PM
      Posts: 2	Life-cycle costs references, please? Rate this comment: (Reply)

      • 	yes - REFERENCES!! OptiPes on 07/09/2007 at 8:20 PM
        Posts: 3	smart people write fat books about total (lifecycle) cost of nuclear energy. simple claims about it has no place on forums like this... Rate this comment: (Reply)

• 	use of SOI valikor on 07/13/2007 at 6:41 AM
  Posts: 1	Is this approach compatible with SOI (silicon on insulator)? Valikor Rate this comment: (Reply)

• Management of radioactive waste jmongu on 08/01/2007 at 11:44 AM

  Posts: 3 Avg Rating:

  We need to assess the risk of management of radioactive waste by the multi-barrier system. Using knowledge of the chemical properties of the various radionuclides in spent fuel, let follows each of the important radionuclides as it travels through the many barriers placed in its path. It turns out that only two radionuclides are able to reach the biosphere, and they arrive at the earth’s surface only after many thousands of years. A careful analysis of the critical points of the disposal plan emphasizes site rejection criteria and other stages at which particular care must be taken, demonstrating how dangers can be anticipated and putting to rest the fear of nuclear fuel waste and its geological burial. Rate this comment: (Reply)

  • Re: Management of radioactive waste Siphon on 08/27/2007 at 4:19 PM

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    The US government is legally entitled, and ultimately also responsible for that waste. There is little hope for privatisation of this, for obvious reasons. Doing a lifecycle cost analysis is rather difficult if the industry cannot be accounted for all costs and responsibilities. This is also very difficult if these particular costs and responsibilities are handed over to future generations and governments. Then there are the weapon implications, which only cause more gov't meddling. No thanks, let's not go the France route. It's bad enough already with current government energy policy. Rate this comment: (Reply)

    • 	Re: Management of radioactive waste CarlHitchon on 10/16/2007 at 1:53 AM
      Posts: 14 Avg Rating:	This is just one of many disparaging remarks you have made about nuclear energy.  It works fine in France. Fire can burn, should we give that up?  Nuclear wastes are minute in quantity when compared with fossil fuel wastes.  Nuclear wastes are manageable. The problem with nuclear energy is political as is this anti-nuke attitude. Rate this comment: (Reply)

• 	75% efficient engine? Macrob on 08/05/2007 at 3:31 AM
  Posts: 2	If we can cover internal surface of the combustion engine with this new Photovoltaics then we can capture 40% energy as light, 25% as ordinary engine cycle and next 10% in steam cycle (re six stroke engine) 3% leftover with thermoelectric module. Rate this comment: (Reply)

• solar electrolysis sbkadar on 08/16/2007 at 9:37 PM

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  There are a number of schemes for using the wasted heat that normally passes through solar cells. Since they typically pass IR quite efficiently. These processes use the heat in solid state electrolyzer cells to generate hydrogen from water (actually steam because of the temperature). They work like solid oxide hydrogen fuel cells in reverse. The electricity from the cell powers the dissociation and the heat makes the process more efficient. I'd love to lay my hands on these cells to experiment with. But where can an individual buy such devices? Rate this comment: (Reply)