12 ms·

Let's investigate this! For reference, a common electricity mix currently generates about 0.5 tons of CO2 per MWh [0][1]. Now, for the device in question: C

Let's investigate this! For reference, a common electricity mix currently generates about 0.5 tons of CO2 per MWh [0][1]. Now, for the device in question: Creating 1 ton of cement releases about 1 ton of CO2 [2]. A common ratio of cement per mass of concrete is maybe 1/5 [4]. The article says they found a way to reduce that to a sixth, so we are at about 1/30 of the concrete mass in cement. From the article, each block weighs 35 tons. So we'll just assume 1 ton of cement (and CO2) per block. The graphic in the article shows ~40 layers of no more than 20x6 concrete blocks can be stacked around the tower, each weighing 35 tons. Therefore, each such installation would cost about 5000 tons of cement or CO2. So its building cost in cement alone is the equivalent of 10000 MWh. Fully "charged", it stores 20 MWh. It would therefore have to complete 500 full cycles of taking energy available for free (and otherwise lost) and feed it back. Roughly assuming it can do that every week (no idea, really depends), that would be ten years to become CO2 neutral, just in terms of cement. So there's your reference value. However, I haven't seen this kind of calculation for other energy sources. That would be interesting. Edit: Here is a review of CO2 from lithium-ion batteries: https://www.ivl.se/download/18.5922281715bdaebede9559/1496046218976/C243+The+life+cycle+energy+consumption+and+CO2+emissions+from+lithium+ion+batteries+.pdf https://www.ivl.se/download/18.5922281715bdaebede9559/149604... They say 150-200 tons of CO2-equivalent (!) per MWh stored, which is very close to the device in the article (in the above estimate it would be 250 tons of CO2 per MWh, although I did not check whether that is pure or CO2 equivalent). [0] https://www.eia.gov/electricity/state/ https://www.eia.gov/electricity/state/ (randomly sampled some states) [1] https://www.umweltbundesamt.de/sites/default/files/medien/376/bilder/entwicklung_der_spezifischen_kohlendioxid-emissionen_des_deutschen_strommix_1990-2016.png https://www.umweltbundesamt.de/sites/default/files/medien/37... (German statistics) [2] https://blogs.ei.columbia.edu/2012/05/09/emissions-from-the-cement-industry/ https://blogs.ei.columbia.edu/2012/05/09/emissions-from-the-... [3] https://sans10400.co.za/concrete-mixes-by-weight/ https://sans10400.co.za/concrete-mixes-by-weight/

h4b4n3r0 8y ago
I’ve also read that concrete absorbs CO2, in significant enough quantities that an isolated ecosystem experiment had to be aborted because plants weren’t getting enough of it.
- MauranKilom 8y ago
  I'm not doubting it, but on the other hand I don't think that the cement will re-absorb a significant amount of its own mass in CO2 (which it would have to in order to offset this 1-to-1 CO2 footprint).
  - schiffern 8y ago
    Portland cement is at least 80% CaO, so in theory it's 63% of the cement's dry mass (CaO + CO2 -> CaCO3)[1]. In practice it's ~43% that value, or 27% of the cement's dry mass.[2] [1] https://en.wikipedia.org/wiki/Cement_kiln#Carbon_dioxide https://en.wikipedia.org/wiki/Cement_kiln#Carbon_dioxide [2] https://www.nature.com/articles/ngeo2840 https://www.nature.com/articles/ngeo2840
    - MauranKilom 8y ago
      So apparently it depends on the type of cement - non-hydraulic cement hardens as you described, while hydraulic cement does not absorb CO2 but instead hardens in the presence of water. I guess they wouldn't have a reason to use hydraulic cement for this though, so it seems you're right.
      - schiffern 8y ago
        It's true that hydraulic cements (eg Portland cement) harden by a different mechanism, but they too will fully carbonatate over time. https://www.astm.org/DIGITAL_LIBRARY/STP/PAGES/STP39460S.htm https://www.astm.org/DIGITAL_LIBRARY/STP/PAGES/STP39460S.htm https://nvlpubs.nist.gov/nistpubs/jres/60/jresv60n5p441_A1b.pdf https://nvlpubs.nist.gov/nistpubs/jres/60/jresv60n5p441_A1b.... https://en.wikipedia.org/wiki/Carbonatation https://en.wikipedia.org/wiki/Carbonatation
owengee 8y ago
Worth pointing out that if you're patient with setting times, you can use portland cement substitutes (fly ash, ground blast furnace slag) as a substitute for portland cement. Slower strength times (several days longer) but same long term strength and way lower embodied carbon. The thing i ponder about this is the foundations needed for a setup. Concrete stacks very well (think dams) but you need very strong foundations for tall, solid concrete structures.
mistermann 8y ago
Nice work. From [2]: Cement manufacturing is highly energy- and emissions-intensive because of the extreme heat required to produce it. Producing a ton of cement requires 4.7 million BTU of energy, equivalent to about 400 pounds of coal, and generates nearly a ton of CO2. Given its high emissions and critical importance to society, cement is an obvious place to look to reduce greenhouse gas emissions. Ignoring the geographical problems, could using the power source from which energy is stored for these devices also be used to manufacture the concrete, or would you be constrained by the power plants ability to output enough energy intensity to produce concrete? If feasible to do, then for the geography issue, would the CO2 output from lengthening the trucking route and/or high voltage transmission lines to the storage site possibly overcome the cement issue overall? If the power is ~free, loss in transmission is less important, but then you have to consider the output of manufacturing and installing transmission lines also. Although, perhaps there's spare capacity on some lines. Actually, once the blocks are manufactured, you can ship them anywhere. Complicated.
- CydeWeys 8y ago
  > Actually, once the blocks are manufactured, you can ship them anywhere. But you won't want to, because they're insanely heavy. At 35 tons a semi-trailer can only carry one. You really need to build these on-site. The amount of diesel you'd burn to move them long distance is astronomical.
  - lenzm 8y ago
    If you build it on site won't you still have to haul in all of the materials to produce it which will weigh more than the final product?
    - CydeWeys 8y ago
      The point is that they would be made locally, not "shipped anywhere". Every city has a bunch of local concrete plants for a reason. If I buy aggregate, it's coming from nearby; it's not being shipped across the country.
    - 8y ago
bluthru 8y ago
>that would be ten years to become CO2 neutral, just in terms of cement Goodness, this doesn't seem viable at all. Could the system work with pallets of steel drums filled with water? It looks like 4 layers is usually the height limit.
- theyinwhy 8y ago
  Why not? I would estimate the lifetime being at least 30 years.
  - bluthru 8y ago
    I think the better approach would be to stack limestone (density of 170 lb/ft3 vs. concrete's 150 lb/ft3) and have very little environmental impact. Does it depend on height to be effective, or could it stack limestone just 30' up or so?

h4b4n3r0 8y ago

I’ve also read that concrete absorbs CO2, in significant enough quantities that an isolated ecosystem experiment had to be aborted because plants weren’t getting enough of it.

MauranKilom 8y ago
I'm not doubting it, but on the other hand I don't think that the cement will re-absorb a significant amount of its own mass in CO2 (which it would have to in order to offset this 1-to-1 CO2 footprint).
- schiffern 8y ago
  Portland cement is at least 80% CaO, so in theory it's 63% of the cement's dry mass (CaO + CO2 -> CaCO3)[1]. In practice it's ~43% that value, or 27% of the cement's dry mass.[2] [1] https://en.wikipedia.org/wiki/Cement_kiln#Carbon_dioxide https://en.wikipedia.org/wiki/Cement_kiln#Carbon_dioxide [2] https://www.nature.com/articles/ngeo2840 https://www.nature.com/articles/ngeo2840
  - MauranKilom 8y ago
    So apparently it depends on the type of cement - non-hydraulic cement hardens as you described, while hydraulic cement does not absorb CO2 but instead hardens in the presence of water. I guess they wouldn't have a reason to use hydraulic cement for this though, so it seems you're right.
    - schiffern 8y ago
      It's true that hydraulic cements (eg Portland cement) harden by a different mechanism, but they too will fully carbonatate over time. https://www.astm.org/DIGITAL_LIBRARY/STP/PAGES/STP39460S.htm https://www.astm.org/DIGITAL_LIBRARY/STP/PAGES/STP39460S.htm https://nvlpubs.nist.gov/nistpubs/jres/60/jresv60n5p441_A1b.pdf https://nvlpubs.nist.gov/nistpubs/jres/60/jresv60n5p441_A1b.... https://en.wikipedia.org/wiki/Carbonatation https://en.wikipedia.org/wiki/Carbonatation

owengee 8y ago

Worth pointing out that if you're patient with setting times, you can use portland cement substitutes (fly ash, ground blast furnace slag) as a substitute for portland cement. Slower strength times (several days longer) but same long term strength and way lower embodied carbon. The thing i ponder about this is the foundations needed for a setup. Concrete stacks very well (think dams) but you need very strong foundations for tall, solid concrete structures.

mistermann 8y ago

Nice work. From [2]: Cement manufacturing is highly energy- and emissions-intensive because of the extreme heat required to produce it. Producing a ton of cement requires 4.7 million BTU of energy, equivalent to about 400 pounds of coal, and generates nearly a ton of CO2. Given its high emissions and critical importance to society, cement is an obvious place to look to reduce greenhouse gas emissions. Ignoring the geographical problems, could using the power source from which energy is stored for these devices also be used to manufacture the concrete, or would you be constrained by the power plants ability to output enough energy intensity to produce concrete? If feasible to do, then for the geography issue, would the CO2 output from lengthening the trucking route and/or high voltage transmission lines to the storage site possibly overcome the cement issue overall? If the power is ~free, loss in transmission is less important, but then you have to consider the output of manufacturing and installing transmission lines also. Although, perhaps there's spare capacity on some lines. Actually, once the blocks are manufactured, you can ship them anywhere. Complicated.

CydeWeys 8y ago
> Actually, once the blocks are manufactured, you can ship them anywhere. But you won't want to, because they're insanely heavy. At 35 tons a semi-trailer can only carry one. You really need to build these on-site. The amount of diesel you'd burn to move them long distance is astronomical.
- lenzm 8y ago
  If you build it on site won't you still have to haul in all of the materials to produce it which will weigh more than the final product?
  - CydeWeys 8y ago
    The point is that they would be made locally, not "shipped anywhere". Every city has a bunch of local concrete plants for a reason. If I buy aggregate, it's coming from nearby; it's not being shipped across the country.
  - 8y ago

bluthru 8y ago

>that would be ten years to become CO2 neutral, just in terms of cement Goodness, this doesn't seem viable at all. Could the system work with pallets of steel drums filled with water? It looks like 4 layers is usually the height limit.

theyinwhy 8y ago
Why not? I would estimate the lifetime being at least 30 years.
- bluthru 8y ago
  I think the better approach would be to stack limestone (density of 170 lb/ft3 vs. concrete's 150 lb/ft3) and have very little environmental impact. Does it depend on height to be effective, or could it stack limestone just 30' up or so?