8 ms·

Interesting - essentially the iron is oxidised to release energy, then deoxidised using renewable energy. So it's another way of buffering renewable energy, whi

Interesting - essentially the iron is oxidised to release energy, then deoxidised using renewable energy. So it's another way of buffering renewable energy, which doesn't require a large body of water to store it. I'd be interested to know the overall efficiency of the process, but it sounds great - on the surface.

pishpash 6y ago
Not even close. Second law of thermodynamics puts a limit on heat engine. Gravity storage is not subject to such limit. But it is a great idea to burn any fuel whose oxidized product is not a gas. The only reason why burning hydrocarbons is problematic is because carbon dioxide is a gas, otherwise it could be captured and recycled like this.
- stkdump 6y ago
  Seems about right. Pumped storage is at about 70% efficiency round-trip, this is 40%. Also, not producing greenhouse gases sounds like a good idea.
- knolax 6y ago
  Well I think in this case the iron is feeding a furnace so it's not going through a heat engine, it's just giving off heat.
  - socialdemocrat 6y ago
    Yes and anyway you could use combined heath and power systems to get higher efficiency.
    - fastball 6y ago
      Not sure I follow.
      - hinkley 6y ago
        Cogeneration. It's common in cogeneration for heat to be a secondary output that makes the overall system profitable, but isn't the primary output.
        fastball 6y ago
        But in this case heat is the primary output.
  - ncmncm 6y ago
    Right, conversion of iron to rust yielding heat is 100% efficient, less only the work needed to move the rust out of the way. If you wanted to convert that heat back to electricity, there would be losses, but nowhere near as much as some people are saying. 1800 degrees minus ambient is a very big delta T. You are not bound to a closed cycle, so Carnot does not apply. So it is likely 80+% would be achievable, maybe over 65% round trip.
- Ensorceled 6y ago
  Gravity storage IS subject to the same law, why do you believe it isn’t? Burning hydrocarbons is problematic for a host of reasons besides CO2 release: fracking, oil spills, release of other pollutants, political issues with the supplier countries, pipelines, ...
  - thereisnospork 6y ago
    Gravity storage is not a heat engine, ergo Carnot's rule does not apply.
    - deleted 6y ago
      [deleted]
    - Ensorceled 6y ago
      But the second law of thermodynamics still does. Gravity wells are still a mechanical system, just not a heat engine.
      - ClumsyPilot 6y ago
        Laws of thermodynamics apply to the entire universe, ergo i dont think anyone is claiming to break laws of physics
      - thereisnospork 6y ago
        >Not even close. Second law of thermodynamics puts a limit on heat engine. Gravity storage is not subject to such limit. Emphasis mine. Don't be a pedant.
        Ensorceled 6y ago
        Well, my important point was that hydrocarbons are fucking terrible but keep focusing on the first part.
      - ergwwrt 6y ago
        2nd law of t only applies to mass. Gravity works via gravitons which are massless so the 2nd does not apply..
bisRepetita 6y ago
>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.
hinkley 6y ago
I've seen designs for renewable energy storage that use gravity. These are often with water, but I've also seen designs using cranes and regenerative braking. I've seen designs like this that use load shedding for generating some useful feedstock material. What I haven't seen is many people doing both at the same time. I might have seen a desal unit powered by green energy, which tops up the water towers when power is cheap, but not much beyond that.

pishpash 6y ago

Not even close. Second law of thermodynamics puts a limit on heat engine. Gravity storage is not subject to such limit. But it is a great idea to burn any fuel whose oxidized product is not a gas. The only reason why burning hydrocarbons is problematic is because carbon dioxide is a gas, otherwise it could be captured and recycled like this.

stkdump 6y ago
Seems about right. Pumped storage is at about 70% efficiency round-trip, this is 40%. Also, not producing greenhouse gases sounds like a good idea.
knolax 6y ago
Well I think in this case the iron is feeding a furnace so it's not going through a heat engine, it's just giving off heat.
- socialdemocrat 6y ago
  Yes and anyway you could use combined heath and power systems to get higher efficiency.
  - fastball 6y ago
    Not sure I follow.
    - hinkley 6y ago
      Cogeneration. It's common in cogeneration for heat to be a secondary output that makes the overall system profitable, but isn't the primary output.
      - fastball 6y ago
        But in this case heat is the primary output.
- ncmncm 6y ago
  Right, conversion of iron to rust yielding heat is 100% efficient, less only the work needed to move the rust out of the way. If you wanted to convert that heat back to electricity, there would be losses, but nowhere near as much as some people are saying. 1800 degrees minus ambient is a very big delta T. You are not bound to a closed cycle, so Carnot does not apply. So it is likely 80+% would be achievable, maybe over 65% round trip.
Ensorceled 6y ago
Gravity storage IS subject to the same law, why do you believe it isn’t? Burning hydrocarbons is problematic for a host of reasons besides CO2 release: fracking, oil spills, release of other pollutants, political issues with the supplier countries, pipelines, ...
- thereisnospork 6y ago
  Gravity storage is not a heat engine, ergo Carnot's rule does not apply.
  - deleted 6y ago
    [deleted]
  - Ensorceled 6y ago
    But the second law of thermodynamics still does. Gravity wells are still a mechanical system, just not a heat engine.
    - ClumsyPilot 6y ago
      Laws of thermodynamics apply to the entire universe, ergo i dont think anyone is claiming to break laws of physics
    - thereisnospork 6y ago
      >Not even close. Second law of thermodynamics puts a limit on heat engine. Gravity storage is not subject to such limit. Emphasis mine. Don't be a pedant.
      - Ensorceled 6y ago
        Well, my important point was that hydrocarbons are fucking terrible but keep focusing on the first part.
    - ergwwrt 6y ago
      2nd law of t only applies to mass. Gravity works via gravitons which are massless so the 2nd does not apply..

bisRepetita 6y ago

>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.

hinkley 6y ago

I've seen designs for renewable energy storage that use gravity. These are often with water, but I've also seen designs using cranes and regenerative braking. I've seen designs like this that use load shedding for generating some useful feedstock material. What I haven't seen is many people doing both at the same time. I might have seen a desal unit powered by green energy, which tops up the water towers when power is cheap, but not much beyond that.