4 ms·

>The maximum thermodynamic efficiency of this cycle is 50% (and likely will be lower). This is not much better than making electricity with the reactor and driv

by scythe 4y ago

>The maximum thermodynamic efficiency of this cycle is 50% (and likely will be lower). This is not much better than making electricity with the reactor and driving electrolysers. The numbers I've found elsewhere dispute this. The World Nuclear Association puts the thermal -> electric conversion efficiency of nuclear plants at around 35% (current) to 40% (best) [1]. A similar but far less corrosive copper-chlorine process is being developed in Canada with preliminary analyses claiming as much as double the efficiency of electrolysis [2]. The maximum thermodynamic efficiency may also be exceeded if waste heat can be converted to electricity simultaneously. With that said, tests of the sulfur-iodine process continue to find that corrosion and damage to the (chemical) reactor components remains limiting, with 20% efficiency lost in H2SO4 splitting over just four days [3]. H2SO4 at 900 C is much more corrosive than HCl at 500 C. 1: https://world-nuclear.org/our-association/publications/technical-positions/cooling-of-power-plants.aspx https://world-nuclear.org/our-association/publications/techn... 2: https://www.sciencedirect.com/science/article/pii/S0360319922043555 https://www.sciencedirect.com/science/article/pii/S036031992... 3: https://www.sciencedirect.com/science/article/pii/S1364032117309231 https://www.sciencedirect.com/science/article/pii/S136403211...

pfdietz 4y ago
Being twice the efficiency of electrolysis with nuclear is not enough, because the levelized cost of electricity ratio between nuclear and renewables is more than 2 (and even more so the ratio between nuclear and surplus renewable output.)
- scythe 4y ago
  Looking at the solar generation LCoE alone, you're correct. The numbers I found for battery LCoE are all over the place, which makes it hard to judge. Assuming $100/kWh and a cycle life of 1000 (close to existing batteries), battery LCoE is high enough to justify nuclear-to-hydrogen. With longer cycle life, which has gone up to 10,000 cycles at lab-scale, that number comes down substantially. Assuming technology improvements, of course, would also have to be applied to nuclear. I was originally interested in thermochemical hydrogen for a solar concentrator source, but a lot of current research seems to focus on nuclear because the thermal energy input is more stable, with an outlook towards solar as the technology is worked out.
  - pfdietz 4y ago
    A life cycle of 1000 is very short, and I don't think it's reasonable to expect that for currently installed batteries. I understand current utility scale batteries are shooting for an eight year lifespan (3000 cycles) with the hope of getting to 10-15 years (but data is lacking to justify that.) Longer cycle life should be proved by the time any nuclear thermochemical hydrogen system could be up and running.
    - jandrese 4y ago
      Assuming a daily charge/discharge a 1000 cycle battery needs to be replaced every 3 years. That would suggest that the majority of installers that guarantee the batteries for 10-15 years are going to lose their shirt on warranty replacements.
      - pfdietz 4y ago
        Which should tell you the 1000 cycle figure is not correct. I mean, they could test the cells to 1000 cycles even faster, by doing 3 charge/discharge cycles a day. They've had time to do that.
      - scythe 4y ago
        Batteries tend to longer if you don't completely drain them in each cycle. I strongly doubt the typical driver covers 200 miles in a day — otherwise cars would only last three years. IIRC you can extend the useful life of a typical Li-ion battery significantly by only charging it to 80% most of the time.
    - scythe 4y ago
      I probably shouldn't have mentioned batteries at all considering that we're comparing hydrogen generation technologies. But the review I found shows cycle life is variable in existing commercial batteries, and generally not much higher than 2000: https://www.nature.com/articles/s41560-019-0356-8 https://www.nature.com/articles/s41560-019-0356-8 The interest in hydrogen is for thermal processes (cement, alumina) and weight-sensitive applications as far as I can see. For electricity storage the fuel cell efficiency is prohibitive.

by scythe 4y ago

pfdietz 4y ago

Being twice the efficiency of electrolysis with nuclear is not enough, because the levelized cost of electricity ratio between nuclear and renewables is more than 2 (and even more so the ratio between nuclear and surplus renewable output.)

scythe 4y ago
Looking at the solar generation LCoE alone, you're correct. The numbers I found for battery LCoE are all over the place, which makes it hard to judge. Assuming $100/kWh and a cycle life of 1000 (close to existing batteries), battery LCoE is high enough to justify nuclear-to-hydrogen. With longer cycle life, which has gone up to 10,000 cycles at lab-scale, that number comes down substantially. Assuming technology improvements, of course, would also have to be applied to nuclear. I was originally interested in thermochemical hydrogen for a solar concentrator source, but a lot of current research seems to focus on nuclear because the thermal energy input is more stable, with an outlook towards solar as the technology is worked out.
- pfdietz 4y ago
  A life cycle of 1000 is very short, and I don't think it's reasonable to expect that for currently installed batteries. I understand current utility scale batteries are shooting for an eight year lifespan (3000 cycles) with the hope of getting to 10-15 years (but data is lacking to justify that.) Longer cycle life should be proved by the time any nuclear thermochemical hydrogen system could be up and running.
  - jandrese 4y ago
    Assuming a daily charge/discharge a 1000 cycle battery needs to be replaced every 3 years. That would suggest that the majority of installers that guarantee the batteries for 10-15 years are going to lose their shirt on warranty replacements.
    - pfdietz 4y ago
      Which should tell you the 1000 cycle figure is not correct. I mean, they could test the cells to 1000 cycles even faster, by doing 3 charge/discharge cycles a day. They've had time to do that.
    - scythe 4y ago
      Batteries tend to longer if you don't completely drain them in each cycle. I strongly doubt the typical driver covers 200 miles in a day — otherwise cars would only last three years. IIRC you can extend the useful life of a typical Li-ion battery significantly by only charging it to 80% most of the time.
  - scythe 4y ago
    I probably shouldn't have mentioned batteries at all considering that we're comparing hydrogen generation technologies. But the review I found shows cycle life is variable in existing commercial batteries, and generally not much higher than 2000: https://www.nature.com/articles/s41560-019-0356-8 https://www.nature.com/articles/s41560-019-0356-8 The interest in hydrogen is for thermal processes (cement, alumina) and weight-sensitive applications as far as I can see. For electricity storage the fuel cell efficiency is prohibitive.