3 ms·

It's always fascinating to me that, no matter how many interesting new ways to release lots of energy we develop, we are still stuck with the same method for co

It's always fascinating to me that, no matter how many interesting new ways to release lots of energy we develop, we are still stuck with the same method for converting it to electricity: release the energy as heat, use heat to make steam, use steam to drive generator.

NateEag 3y ago
Helion is planning to use induction to generate electricity from the fusion reaction's generated magnetic field, IIUC: https://www.helionenergy.com/faq/ https://www.helionenergy.com/faq/ (See "How does Helion generate electricity from fusion?" question)
- MichaelZuo 3y ago
  Which doesn't make sense for power generation since there will always be some percentage of neutrons produced by any type of fusion reaction that can only be useful for generating steam. To entirely skip the steam cycle portion is to intentionally make a much less efficient design. For space-constrained, high-value, applications where economics don't matter that much, such as a submarine, that would make sense, but otherwise...
  - jessriedel 3y ago
    You could always add the liquid metal blanket if you want to eke out the extra 10% (or if you want to generate tritium). But it's not worth the complication in an early prototype.
  - gus_massa 3y ago
    They plan to use 2D + 3He -> 4He + 1H, so no neutrons https://en.wikipedia.org/wiki/Aneutronic_fusion#Candidate_reactions https://en.wikipedia.org/wiki/Aneutronic_fusion#Candidate_re... (I'm still not convinced of their explanations, but a fast proton may be easy to catch by the magnetic field and create the effect they want.)
    - fastneutron 3y ago
      Nitpick: You’re always going to get some parasitic D+D reactions because it’s reaction cross section is appreciably higher than D + 3He below 50 keV, and non-negligible even after the crossover point.
      - skykooler 3y ago
        Doesn't D+D just yield 4He (and no neutrons) though?
        philipkglass 3y ago
        It yields 3He plus a 2.45 MeV neutron at least part of the time. See the diagram here: https://undsci.berkeley.edu/teach-resources/products-of-deuterium-fusion/ https://undsci.berkeley.edu/teach-resources/products-of-deut...
  - DennisP 3y ago
    Helion's fuel mix produces just 6% of its energy as neutron radiation, and if you harvest it you'll lose a third of that. As long as you have enough net energy, collecting that 4% might not make financial sense. With fuel costs insignificant, your cost per kWh is mainly capital cost. Let's say it's all capital just to keep it simple. I don't know how much the input energy will be but if your choice is between, say, generating net energy of 50MW without a turbine or 54MW with a turbine, then you would skip the turbine if it adds more than 8% to the capital cost. I suspect Helion has done this calculation in detail.
    - MichaelZuo 3y ago
      It does seem to hinge on the cost of fuel, I have some doubts about whether they can secure a fuel supply so cheap as to skip out on that extra 4 MW, even after factoring in the cost of a small steam turbine installation.
      - DennisP 3y ago
        Deuterium costs several thousand dollars/kilogram. But even though it is just one part in several thousand of the hydrogen in water, there's enough deuterium in your morning shower to provide all your energy needs for a year.[1] Cost of deuterium is definitely insignificant. Helion's other fuel is helium-3 which they'll make themselves by fusing deuterium. So the helium-3 cost will directly depend on the capital cost of the reactor producing it. (This may be the same reactor, both generating electricity and breeding He3. Or they may use dedicated He3 breeders, and minimize the D-D reactions in the generators.) [1] https://dothemath.ucsd.edu/2012/01/nuclear-fusion/ https://dothemath.ucsd.edu/2012/01/nuclear-fusion/
- tsimionescu 3y ago
  Helion is planning to use a different fusion reaction, one where the bulk of the energy will be coming out as charged particles, not neutrons. However, D+T fusion is the only type of fusion that we have been able to sustain for any significant amount of time with reasonable energy inputs. What Helion is planning to do is completely unexplored and requires some major scientific advances.
jessriedel 3y ago
The reason just that this is a simple process for which a steam turbine can achieves 90% of the thermodynamic optimum. To my knowledge, the only reason people consider alternatives is to reduce capital costs. You're still capped by thermodynamics though.
- nerdponx 3y ago
  That's what I was wondering: if heat -> steam -> turbine is close enough to the theoretical upper limit and you get diminishing returns by other means. Still, it seems very indirect. Like generating solar power by using a parabolic mirror to heat water instead of photovoltaic panels... but of course I just found an example of doing that too: https://en.wikipedia.org/wiki/Parabolic_trough https://en.wikipedia.org/wiki/Parabolic_trough
  - Iulioh 3y ago
    There are multiple solutions of that sort but all failed due to high maintenance costs Usually the liquid is some sort of oil that csn reach higher temperature and then the oil is used to heat water Another design uses hundreds of mirror centered around a high tower with molten salts as the heat medium The really good part of this design is that the molted salts can produce energy for 3-4h after the sun is set.
sambapa 3y ago
It's because we're in local maximum - steam turbines are just so developed
tsimionescu 3y ago
Well, we do have some other strategies. Hydro and wind just turn the turbine mechanically, they don't heat up water to make steam. And photovoltaics create electricity directly using an effect that won Einstein the Nobel prize and began the age of quantum mechanics, so that's about as advanced as they come.
rocqua 3y ago
Steam turbines are actually quite a bad method, because pure heat is a difficult energy source. It's just also a very available energy source. The 90% efficiency quoted in the comments is 90% of theoretical maximum efficiency. This theoretical maximum is about 50% for the best systems.

NateEag 3y ago

Helion is planning to use induction to generate electricity from the fusion reaction's generated magnetic field, IIUC: https://www.helionenergy.com/faq/ https://www.helionenergy.com/faq/ (See "How does Helion generate electricity from fusion?" question)

MichaelZuo 3y ago
Which doesn't make sense for power generation since there will always be some percentage of neutrons produced by any type of fusion reaction that can only be useful for generating steam. To entirely skip the steam cycle portion is to intentionally make a much less efficient design. For space-constrained, high-value, applications where economics don't matter that much, such as a submarine, that would make sense, but otherwise...
- jessriedel 3y ago
  You could always add the liquid metal blanket if you want to eke out the extra 10% (or if you want to generate tritium). But it's not worth the complication in an early prototype.
- gus_massa 3y ago
  They plan to use 2D + 3He -> 4He + 1H, so no neutrons https://en.wikipedia.org/wiki/Aneutronic_fusion#Candidate_reactions https://en.wikipedia.org/wiki/Aneutronic_fusion#Candidate_re... (I'm still not convinced of their explanations, but a fast proton may be easy to catch by the magnetic field and create the effect they want.)
  - fastneutron 3y ago
    Nitpick: You’re always going to get some parasitic D+D reactions because it’s reaction cross section is appreciably higher than D + 3He below 50 keV, and non-negligible even after the crossover point.
    - skykooler 3y ago
      Doesn't D+D just yield 4He (and no neutrons) though?
      - philipkglass 3y ago
        It yields 3He plus a 2.45 MeV neutron at least part of the time. See the diagram here: https://undsci.berkeley.edu/teach-resources/products-of-deuterium-fusion/ https://undsci.berkeley.edu/teach-resources/products-of-deut...
- DennisP 3y ago
  Helion's fuel mix produces just 6% of its energy as neutron radiation, and if you harvest it you'll lose a third of that. As long as you have enough net energy, collecting that 4% might not make financial sense. With fuel costs insignificant, your cost per kWh is mainly capital cost. Let's say it's all capital just to keep it simple. I don't know how much the input energy will be but if your choice is between, say, generating net energy of 50MW without a turbine or 54MW with a turbine, then you would skip the turbine if it adds more than 8% to the capital cost. I suspect Helion has done this calculation in detail.
  - MichaelZuo 3y ago
    It does seem to hinge on the cost of fuel, I have some doubts about whether they can secure a fuel supply so cheap as to skip out on that extra 4 MW, even after factoring in the cost of a small steam turbine installation.
    - DennisP 3y ago
      Deuterium costs several thousand dollars/kilogram. But even though it is just one part in several thousand of the hydrogen in water, there's enough deuterium in your morning shower to provide all your energy needs for a year.[1] Cost of deuterium is definitely insignificant. Helion's other fuel is helium-3 which they'll make themselves by fusing deuterium. So the helium-3 cost will directly depend on the capital cost of the reactor producing it. (This may be the same reactor, both generating electricity and breeding He3. Or they may use dedicated He3 breeders, and minimize the D-D reactions in the generators.) [1] https://dothemath.ucsd.edu/2012/01/nuclear-fusion/ https://dothemath.ucsd.edu/2012/01/nuclear-fusion/
tsimionescu 3y ago
Helion is planning to use a different fusion reaction, one where the bulk of the energy will be coming out as charged particles, not neutrons. However, D+T fusion is the only type of fusion that we have been able to sustain for any significant amount of time with reasonable energy inputs. What Helion is planning to do is completely unexplored and requires some major scientific advances.

jessriedel 3y ago

The reason just that this is a simple process for which a steam turbine can achieves 90% of the thermodynamic optimum. To my knowledge, the only reason people consider alternatives is to reduce capital costs. You're still capped by thermodynamics though.

nerdponx 3y ago
That's what I was wondering: if heat -> steam -> turbine is close enough to the theoretical upper limit and you get diminishing returns by other means. Still, it seems very indirect. Like generating solar power by using a parabolic mirror to heat water instead of photovoltaic panels... but of course I just found an example of doing that too: https://en.wikipedia.org/wiki/Parabolic_trough https://en.wikipedia.org/wiki/Parabolic_trough
- Iulioh 3y ago
  There are multiple solutions of that sort but all failed due to high maintenance costs Usually the liquid is some sort of oil that csn reach higher temperature and then the oil is used to heat water Another design uses hundreds of mirror centered around a high tower with molten salts as the heat medium The really good part of this design is that the molted salts can produce energy for 3-4h after the sun is set.

sambapa 3y ago

It's because we're in local maximum - steam turbines are just so developed

tsimionescu 3y ago

Well, we do have some other strategies. Hydro and wind just turn the turbine mechanically, they don't heat up water to make steam. And photovoltaics create electricity directly using an effect that won Einstein the Nobel prize and began the age of quantum mechanics, so that's about as advanced as they come.

rocqua 3y ago

Steam turbines are actually quite a bad method, because pure heat is a difficult energy source. It's just also a very available energy source. The 90% efficiency quoted in the comments is 90% of theoretical maximum efficiency. This theoretical maximum is about 50% for the best systems.