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This discussion relates to Technology Review's article Sun + Water = Fuel.

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  maclod
  

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  10/21/2008 08:15 AM

  sensationalisation

  This discovery has much merits on its own. If I read it correctly, this is supposed to be an improved version of electrolysis, which would help in storing electrical energy generated by solar cells. This is a great advancement definitely, since no battery or capacitor can as yet come close to storing as much energy as in chemical bonds.
  
  But improved electrolysis is NOT photosynthesis! Claiming that this discovery amounts to artificial photosynthesis is blatant false representation!
  
  In addition, I wonder if any of the research group has done a check into the energy expenditure required to run the suggested energy storage and recovery system (pumps to move H20, H2 and O2, compress H2 to store it, the necessary catalyst for a fuel cell, the life span of the entire system). Solar cells currently aren't exactly highly efficient, and I wonder if the external energy costs involved might not simply be too much?

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    Kevin Bullis
    

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    10/22/2008 09:54 AM

    Re: sensationalisation

    Maclod--check out my long comment above.

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      Bruceahz
      

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      10/23/2008 10:54 AM

      Re: sensationalisation

      First, thanks Kevin for addressing my previous question (what am I missing), and second I guess you've gotten the message that you have a journalistic responsibility to temper the claims of the folks you write about!
      
      I'm not a botanist so I don't know if plants really have a 2-step process in which the first strips the H and the O apart, but I do know that the "magic" of photosynthesis is that water and CO2 are converted to O2 and hydrocarbon chains with the addition of photon energy.
      
      Hydrocarbon chains are much easier to transport and store than H2 and fit nicely with current electric generation technology.
      
      If the carbon in the hydrocarbon chains comes from CO2, then this becomes a carbon neutral energy source.
      
      Thus, improved electrolysis, while interesting, is not photosynthesis and to my eye a long way from it. Show me a solar panel with water and air flowing through it, that absorbs sunlight, and that generates O2 at one port and a combustible hydrocarbon at another and then we'll have something really worth touting.

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      maclod
      

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      10/27/2008 03:46 AM

      Re: sensationalisation

      Thanks Kevin for your reply!
      
      My sentiments with Bruceahz on journalistic responsibility.
      
      I don't see how useful this catalyst would be in a Graetzel cell though. One selling point of such a cell is its thinness, so how will the designers provide a constant supply of water to the cell for continuous reaction?

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  MakeSense
  

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  10/25/2008 01:23 PM

  All the old questions linger

  It seems as though Dr. Nocera is happy with his results, so his imagination leads him to make claims that "all the old questions" are somehow ended by this. At first, I thought the article might have been about a novel way to produce hydrogen cheaply and in large quantities from sunlight, but it turns out to be an adjunct technology to photovoltaics.
  
  I'm not convinced that hydrogen is cheap or practical to store. But I'm really not convinced that this innovation does not simply add cost to and lower efficiency of PV, but to a lesser degree than existing electrolyzers.
  
  Kevin, could you research an article on V-Fuel Pty Ltd, an Australian comany that is about to manufacture a new generation of flow battery? They estimate the cost to store a kWh of electricity at about a penny, easily made up by the difference in electricity costs between peak and off-peak periods. Such a breakthrough technology would genuinely usher in a change in the renewable energy landscape, particularly as it relates to wind power and to some extent solar options.
  
  The best areas for sunlight are still quite distant from other cloudy areas that need energy. This brings to mind the old, old question of hydrogen transportation, an aspect of hydrogen's usefulness that has yet to be tackled. Hydrogen is notoriously difficult and expensive to transport. Additional steps to catalyze a liquid hydrocarbon would be useful in solving the transport problem, but such steps would themselves be costly of energy and money.
  
  As far as the appearance that using this new technique to electrolyze water could in fact produce fresh water from salt water, the old adage applies: there ain't no free lunch. I suggest that some of the researcher's comments are more wonderment than fully analyzed thoughts.

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    MarionMeads
    

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    10/26/2008 03:34 AM

    Re: All the old questions linger

    It is about Vanadium Redox flow batteries
    http://en.wikipedia.org/wiki/Vanadium_redox_battery
    
    http://thefraserdomain.typepad.com/energy/2006/01/vandium_reflux_.html
    
    "The cost is quoted in $/kWh or $/MWh since the VRB is an "Energy Storage System" and should not be considered a UPS or even a generator. Although the VRB provides the full UPS capability, its primary use is for energy storage for long periods, which UPS and conventional technologies cannot provide. As an approximate cost, systems are priced between $350-$600 per kWh, sizes ranging from a few hundred kW's to MW size systems. As the size of the system in kWh increases, the cost per unit decreases significantly. For example, a system rated at 100MWh would have an installed cost of about $325 per kWh. The incremental cost of storage for large systems is approximately $150 per kWh."
    
    That is very costly storage!!!
    Where did the penny per kWH come from?

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      MakeSense
      

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      10/26/2008 12:57 PM

      Re: All the old questions linger

      The question is, "If a battery costs $150/kWh, how does that translate into a penny per kWh?"
      
      A battery stores electrical energy measured in kilowatt-hours. Also batteries charge and recharge many times over their useful lives. So a 1-kWh battery that has a 20,000-cycle life actually stores 20,000 kWh hours before it must be replaced. The $150 cost is for the battery, but the 1-cent cost is for any kWh that is stored then sold at a later time. $150/20,000 is less than a penny, but other costs must also be factored in that round to a penny per stored kWh. One of those factors is the energy lost in the process of charge/discharge, which is about 20% in this case.
      
      I hope that answers your question. There is a lot of confusion about energy, power and capacity units related to electricity, generation, transmission and storage.

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        MarionMeads
        

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        10/27/2008 10:04 PM

        Re: All the old questions linger

        I wonder what wholesale prices are for electricity. I am in the tiered 3 residential, and electricity costs $0.30/kWH. A storage of 20% losses would mean a loss of 6 cents per kilowatt hour, and that's just the losses alone. Plus the batteries might cost an arm and a leg at retail guys like me, so it would cost about $350/kWH of storage battery. Assuming 20,000 cycles for the lifetime, and each day it cycles, that would be 54.757 years. So the depreciation would be $6.39/year or 1.75 cents per day. Now if I've had this financed at 7.25% APR for 10 years, the $350 investment would cost me $4.11/month or 13.7 cents per day, paid off after 10 years.
        
        So on the retail side of things, it would cost me
        losses: 6 cents/day/kwh
        depreciation: 1.75 cents/day/kwh
        payments: 13.7 cents/day/kwh (10 years only)
        
        That is a hefty price tag of 21.45 cents per day per kwh for the first 10 years and then 7.75 cents for 45 years more.

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        Siphon
        

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        12/05/2008 12:25 PM

        Re: All the old questions linger

        Keep in mind to add interest. Could easily double the cost per kWh of charge/discharge.
        
        Plus pumps maintenance and replacement. Your electrolyte might last 20,000 cycles if it is uncontaminated. But the pumps would typically have to be replaced in maybe 3000-5000 cycles. They are expensive per kW, and require some maintenance.
        
        If your electricity costs 10 cents/kWh (about the US average) you lose 2 cents/kWh in charge/discharge if the cycle is 80% efficient. I don't see how the system cost would be under 2 cents/kWh, considering system O&M and interest rates. So 4 cents/kWh would actually be optimistic for today's tech. It's likely to go down though.
        
        That said I'm worried about the vanadium availability. It's not a very common material. If vanadium utilisation per kWh storage can be increased (eg via increased energy density electrolytes) then this problem could be solved.

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  vlashua
  

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  11/01/2008 09:32 AM

  Drill, Baby, Drill

  The earth has a magnificent internal energy battery. Humans have built relatively reliable energy conversion, transport and portable energy storage systems. And there is an unlimited supply of energy five or ten miles from everywhere on earth ... straight down!
  
  I've been sharing this cutesy image "since the Whole Earth Catalog" and since Athelstan Spillhaus shared his visions in the comics in the '50s.
  
  Take a look at a recent patent for a process idea seriously developed over the last six years by the University of Oklahoma: US Patent 7251938, http://www.google.com/patents?q=7251938&btnG=Search+Patents .
  
  Among other things, the idea uses available technology and could use hot air, steam or hot water to drive turbines without atmospheric contamination or transportation of fuel (horizontally, at least!). Nearby cities could even use wastewater as a water supply and the output for derivative power or agriculture.
  
  The heat of the Earth could provide humans with energy till the sun envelopes it in a couple of billion years -- without technological miracles. According to the patent, such a geothermal plant could provide the output of 10 Hoover Dams (or 10 nuclear plants) with about a tenth of the environmental footprint or impact at less than half the cost. This is MIT, isn't it? How about some peer review?
  
  Drill, Baby, Drill.

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