3 ms·

> only ~20-30% of the energy in the fuel turns into useful work, while electricity is much, much more efficient. So, we need much less of it. Isn't a lot of en

by foota 2mo ago

> only ~20-30% of the energy in the fuel turns into useful work, while electricity is much, much more efficient. So, we need much less of it. Isn't a lot of energy used for heating, not work?

bluGill 2mo ago
Maybe, but that other 70-80% is waste - we could turn it into useful heat, but instead we vent it to the environment. I've seen plans to run an engine in your furnace, thus creating both electric (at 20-30%, and capturing the rest as heat to the house. I've never seen this in the real world and experts who have looked as those systems said they won't enter a building that has one using that design. (it is possible to make a design they would trust, but they haven't seen any)
ZeroGravitas 2mo ago
Yes but by a weird coincidence most of that heat can be provided by heat pumps at a similar 3-5x ratio.
- inigyou 2mo ago
  (it's not a coincidence, it's the exact opposite formula. You can only get 20% out of a certain heat engine because running it in reverse would be a 500% efficient heat pump, and the closed loop can't be more than 100%. This still applies even if the engine isn't built to be able to act as a heat pump, because some other engine could.)
  - ragebol 2mo ago
    I don't see why that would be the case. Why is the 20% of eg. an internal combustion engine coupled to the 500% COP of a heat pump? I see a vague connection as an ICE also uses expanding gasses etc, but that's about it. What am I missing?
    - inigyou 2mo ago
      An ICE is not an ideal heat engine. But if you did have an ideal heat engine, it could either produce work by reducing a temperature difference, or increase a temperature difference when provided with work. No physical device can do better than an ideal heat engine.
      - ragebol 2mo ago
        Ah, thanks, had to be something like that indeed. Had a hard time imagining putting work into an ICE and getting anything useful out.
ragebol 2mo ago
True. For residential heating, heat pumps make for a similar ratio as they make 3-5 units of hear for 1 unit of electric energy, depending on conditions. The challenge in heating is industrial heat, which is much hotter. Can't do that with heat pumps (yet?)
- roryirvine 2mo ago
  Process heat would be a good use case for SMR nuclear if the economics turn out to be favourable (a big if, admittedly). Also potential for using green hydrogen (though the economics of that are even more iffy). Even without those, the continued decrease in solar costs means that there's a decent chance that plain old resistive heating will become viable at some point in the 2040s.

by foota 2mo ago

> only ~20-30% of the energy in the fuel turns into useful work, while electricity is much, much more efficient. So, we need much less of it. Isn't a lot of energy used for heating, not work?

bluGill 2mo ago

Maybe, but that other 70-80% is waste - we could turn it into useful heat, but instead we vent it to the environment. I've seen plans to run an engine in your furnace, thus creating both electric (at 20-30%, and capturing the rest as heat to the house. I've never seen this in the real world and experts who have looked as those systems said they won't enter a building that has one using that design. (it is possible to make a design they would trust, but they haven't seen any)

ZeroGravitas 2mo ago

Yes but by a weird coincidence most of that heat can be provided by heat pumps at a similar 3-5x ratio.

inigyou 2mo ago
(it's not a coincidence, it's the exact opposite formula. You can only get 20% out of a certain heat engine because running it in reverse would be a 500% efficient heat pump, and the closed loop can't be more than 100%. This still applies even if the engine isn't built to be able to act as a heat pump, because some other engine could.)
- ragebol 2mo ago
  I don't see why that would be the case. Why is the 20% of eg. an internal combustion engine coupled to the 500% COP of a heat pump? I see a vague connection as an ICE also uses expanding gasses etc, but that's about it. What am I missing?
  - inigyou 2mo ago
    An ICE is not an ideal heat engine. But if you did have an ideal heat engine, it could either produce work by reducing a temperature difference, or increase a temperature difference when provided with work. No physical device can do better than an ideal heat engine.
    - ragebol 2mo ago
      Ah, thanks, had to be something like that indeed. Had a hard time imagining putting work into an ICE and getting anything useful out.

ragebol 2mo ago

True. For residential heating, heat pumps make for a similar ratio as they make 3-5 units of hear for 1 unit of electric energy, depending on conditions. The challenge in heating is industrial heat, which is much hotter. Can't do that with heat pumps (yet?)

roryirvine 2mo ago
Process heat would be a good use case for SMR nuclear if the economics turn out to be favourable (a big if, admittedly). Also potential for using green hydrogen (though the economics of that are even more iffy). Even without those, the continued decrease in solar costs means that there's a decent chance that plain old resistive heating will become viable at some point in the 2040s.