5 ms·

>I'd be interested to know the overall efficiency of the process, From the article: "High-efficiency electrolysis of iron oxide can store as much as 80 percen

>I'd be interested to know the overall efficiency of the process, From the article: "High-efficiency electrolysis of iron oxide can store as much as 80 percent of your input energy in the iron fuel" "Using this kind of cyclical process to generate electricity could approach a theoretical efficiency around 40 percent"

jillesvangurp 6y ago
Not bad; of course there is also the energy cost related to moving the material around. Iron is kind of heavy. If you are doing the electrolysis on site that's probably not a big factor. But if we're talking about converting coal plants (which the article does), presumably the electrolysis would happen elsewhere; which means tons of iron needs to be moved back and forth. Moving fuel around is also a problem with coal and oil. We're basically burning fossil fuels to move fossil fuels around. In the case of oil, we than also have to run it through energy intensive processes to turn it into more palatable fuels than bunker oil, which is what is typically used for shipping things around. A typical oil tanker consumes a couple of hundreds of tons of bunker fuel per day to move a couple of thousands of tons of fuel around. So, that's a sizable percentage of its load that is lost just to get the raw product from A to B. I'm sure the math is similar for producing and moving coal around. It only makes sense if you get to pollute at will without financial consequences; which happens to be the case with shipping, which mostly takes place in international waters without any constraints or regulations on the amount of crap put in our atmosphere. Ships actually switch to cleaner fuels when they get close to populated areas because otherwise they'd end up killing some of the locals with their fumes. Bunker fuel is nasty. Even more so than coal. So, if we are debating efficiencies, we'd do well to apply the same scrutiny to existing solutions as well. The efficiency of coal should also include digging it up using diesel burning heavy duty equipment, moving it around, etc. I'd bet that knocks some percentage points of even the most efficient plants or ICE cars.
- akie 6y ago
  > But if we're talking about converting coal plants (which the article does), presumably the electrolysis would happen elsewhere; which means tons of iron needs to be moved back and forth. You could build the infrastructure to do the electrolysis immediately next to the coal plant to solve this problem. If this technology takes off that's most likely what will happen anyway.
  - eptcyka 6y ago
    Generating electricity with iron as fuel would be suboptimal, that's like using electricity to turn co2 back into coal, and then using said coal to generate electricity again. Using iron in coal power plants would only male sense if transporting it from somewhere where IRS more efficient to produce iron is economically viable - say use solar in Spain to regenerate iron and then use it further up north where solar isn't as good.
    - Ensorceled 6y ago
      The problem being solved is the bursty nature of green energy, we are trying to store solar energy generated during the day for usage at night or store excess wind energy for still days. We are not trying to transfer green energy to less windy/less sunny places, the grid can take care of that.
      - fastball 6y ago
        Right, but in that case you'll get way better efficiency out of pretty much any other proposed solution: gravity, momentum, battery solutions are all more efficient than this for storing energy from renewables.
        wcarron 6y ago
        Batteries are expensive. Iron is abundant and cheap, and these seem much less difficult/costly to build than to create a dam, for example. It also seems like it can make use of existing infrastructure and save money there.
        fastball 6y ago
        I don’t think the expense of other solutions justifies the abject inefficiency of this one though.
        chongli 6y ago
        Yeah, or in the article’s case (where you’re brewing beer), you might as well use a solar furnace to boil water directly with sunlight. You’ll have a hard time beating that efficiency with other methods. If you have huge water storage tanks anyway then keeping the water hot overnight is not a problem either.
- ximeng 6y ago
  https://www.hellenicshippingnews.com/how-many-gallons-of-fuel-does-a-container-ship-carry/ https://www.hellenicshippingnews.com/how-many-gallons-of-fue... This article suggests at top speed Panamax tankers carry 1.5-2mn gallons of fuel while burning 63,000 gallons per day (i.e. around 3-4% of capacity) at top speed. That is considerably less than the 10% (200 tons to move 2,000 tons) that you suggest. Also the article notes that reducing speed by 10% can reduce fuel use by a third. The tankers travel at 19mph, significantly less than their top speed of 23-28mph so fuel consumption is likely closer to 1%.
  - jillesvangurp 6y ago
    I was talking about the whole journey. You don't get anywhere in this world in less than a few days/weeks with a big oil tanker.
    - nkurz 6y ago
      > A typical oil tanker consumes a couple of hundreds of tons of bunker fuel per day to move a couple of thousands of tons of fuel around. While it certainly makes sense to calculate for the entire journey, if you were talking about the "whole journey" why did you specify "per day"? It's hard to blame 'ximeng' for relying on your written comment rather than what you intended to say. :)
- kybernetikos 6y ago
  Rust is heavier than the equivalent amount of pure iron, so perhaps it would be possible to put the furnace at the top of a hill and the refiner stage at the bottom and let the weight difference do the heavy lifting.
  - socialdemocrat 6y ago
    Haha, love that solution!
  - ajnin 6y ago
    Interesting idea. I wonder how much height difference you would need so that gravity gives you enough energy to power the regenerator at the bottom? The actual energy would come from ... the gravity field of the Earth?
    - bluGill 6y ago
      The energy comes from the mass of oxygen that is released at the bottom and captured at the top. But second law of thermo dynamics applies. If this works at all it is because you are capturing a little more of the energy that was put in at the top and would otherwise be lost. You stil need to put in external energy to keep this system running.
      - cma 6y ago
        Shouldn't the needed energy increase the more the height difference? Seems it must be made up for in some other place too, or less waste heat at some stage.
        bluGill 6y ago
        The energy out increases by the height level as well. If the process was 100% reversible, and friction free (probably a couple other loss factors I forgot about) it would be energy positive as the oxygen is making its way back up in the air is an external energy input. Of course in the real world both assumptions are wrong by more than enough that you can never get this to work.
- socialdemocrat 6y ago
  It is easy to get too hung up on efficiency though. Overall cost matters more. If a solar plus metal powder solution gives the same reliable power as a solar plus battery solution at lower cost then that will often be a superior solution, even if it requires more solar panels. Efficiency matters when you run out of space or resources. But you got vast areas like Sahara where solar power production could be combined with metal production. Wasting space in Sahara is a non-issue if it means you get the overall cost of system down.

jillesvangurp 6y ago

Not bad; of course there is also the energy cost related to moving the material around. Iron is kind of heavy. If you are doing the electrolysis on site that's probably not a big factor. But if we're talking about converting coal plants (which the article does), presumably the electrolysis would happen elsewhere; which means tons of iron needs to be moved back and forth. Moving fuel around is also a problem with coal and oil. We're basically burning fossil fuels to move fossil fuels around. In the case of oil, we than also have to run it through energy intensive processes to turn it into more palatable fuels than bunker oil, which is what is typically used for shipping things around. A typical oil tanker consumes a couple of hundreds of tons of bunker fuel per day to move a couple of thousands of tons of fuel around. So, that's a sizable percentage of its load that is lost just to get the raw product from A to B. I'm sure the math is similar for producing and moving coal around. It only makes sense if you get to pollute at will without financial consequences; which happens to be the case with shipping, which mostly takes place in international waters without any constraints or regulations on the amount of crap put in our atmosphere. Ships actually switch to cleaner fuels when they get close to populated areas because otherwise they'd end up killing some of the locals with their fumes. Bunker fuel is nasty. Even more so than coal. So, if we are debating efficiencies, we'd do well to apply the same scrutiny to existing solutions as well. The efficiency of coal should also include digging it up using diesel burning heavy duty equipment, moving it around, etc. I'd bet that knocks some percentage points of even the most efficient plants or ICE cars.

akie 6y ago
> But if we're talking about converting coal plants (which the article does), presumably the electrolysis would happen elsewhere; which means tons of iron needs to be moved back and forth. You could build the infrastructure to do the electrolysis immediately next to the coal plant to solve this problem. If this technology takes off that's most likely what will happen anyway.
- eptcyka 6y ago
  Generating electricity with iron as fuel would be suboptimal, that's like using electricity to turn co2 back into coal, and then using said coal to generate electricity again. Using iron in coal power plants would only male sense if transporting it from somewhere where IRS more efficient to produce iron is economically viable - say use solar in Spain to regenerate iron and then use it further up north where solar isn't as good.
  - Ensorceled 6y ago
    The problem being solved is the bursty nature of green energy, we are trying to store solar energy generated during the day for usage at night or store excess wind energy for still days. We are not trying to transfer green energy to less windy/less sunny places, the grid can take care of that.
    - fastball 6y ago
      Right, but in that case you'll get way better efficiency out of pretty much any other proposed solution: gravity, momentum, battery solutions are all more efficient than this for storing energy from renewables.
      - wcarron 6y ago
        Batteries are expensive. Iron is abundant and cheap, and these seem much less difficult/costly to build than to create a dam, for example. It also seems like it can make use of existing infrastructure and save money there.
        fastball 6y ago
        I don’t think the expense of other solutions justifies the abject inefficiency of this one though.
      - chongli 6y ago
        Yeah, or in the article’s case (where you’re brewing beer), you might as well use a solar furnace to boil water directly with sunlight. You’ll have a hard time beating that efficiency with other methods. If you have huge water storage tanks anyway then keeping the water hot overnight is not a problem either.
ximeng 6y ago
https://www.hellenicshippingnews.com/how-many-gallons-of-fuel-does-a-container-ship-carry/ https://www.hellenicshippingnews.com/how-many-gallons-of-fue... This article suggests at top speed Panamax tankers carry 1.5-2mn gallons of fuel while burning 63,000 gallons per day (i.e. around 3-4% of capacity) at top speed. That is considerably less than the 10% (200 tons to move 2,000 tons) that you suggest. Also the article notes that reducing speed by 10% can reduce fuel use by a third. The tankers travel at 19mph, significantly less than their top speed of 23-28mph so fuel consumption is likely closer to 1%.
- jillesvangurp 6y ago
  I was talking about the whole journey. You don't get anywhere in this world in less than a few days/weeks with a big oil tanker.
  - nkurz 6y ago
    > A typical oil tanker consumes a couple of hundreds of tons of bunker fuel per day to move a couple of thousands of tons of fuel around. While it certainly makes sense to calculate for the entire journey, if you were talking about the "whole journey" why did you specify "per day"? It's hard to blame 'ximeng' for relying on your written comment rather than what you intended to say. :)
kybernetikos 6y ago
Rust is heavier than the equivalent amount of pure iron, so perhaps it would be possible to put the furnace at the top of a hill and the refiner stage at the bottom and let the weight difference do the heavy lifting.
- socialdemocrat 6y ago
  Haha, love that solution!
- ajnin 6y ago
  Interesting idea. I wonder how much height difference you would need so that gravity gives you enough energy to power the regenerator at the bottom? The actual energy would come from ... the gravity field of the Earth?
  - bluGill 6y ago
    The energy comes from the mass of oxygen that is released at the bottom and captured at the top. But second law of thermo dynamics applies. If this works at all it is because you are capturing a little more of the energy that was put in at the top and would otherwise be lost. You stil need to put in external energy to keep this system running.
    - cma 6y ago
      Shouldn't the needed energy increase the more the height difference? Seems it must be made up for in some other place too, or less waste heat at some stage.
      - bluGill 6y ago
        The energy out increases by the height level as well. If the process was 100% reversible, and friction free (probably a couple other loss factors I forgot about) it would be energy positive as the oxygen is making its way back up in the air is an external energy input. Of course in the real world both assumptions are wrong by more than enough that you can never get this to work.
socialdemocrat 6y ago
It is easy to get too hung up on efficiency though. Overall cost matters more. If a solar plus metal powder solution gives the same reliable power as a solar plus battery solution at lower cost then that will often be a superior solution, even if it requires more solar panels. Efficiency matters when you run out of space or resources. But you got vast areas like Sahara where solar power production could be combined with metal production. Wasting space in Sahara is a non-issue if it means you get the overall cost of system down.