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> oil products have energy density that batteries are barely starting to be capable of Not even close, diesel/gasoline stores 35 MJ/l, a good battery (lithium-

> oil products have energy density that batteries are barely starting to be capable of Not even close, diesel/gasoline stores 35 MJ/l, a good battery (lithium-metal, much better than lithium-ion), 4.32 MJ/l Now, if only we could extract 90% of that diesel stored energy.

CydeWeys 8y ago
If you can't actually extract it (because of limitations like Carnot efficiency, etc.), does it actually count? What's the real figure for usable energy in diesel?
- maxerickson 8y ago
  Depends on what you are doing. An awful lot of energy consumption is just fine with waste heat, it doesn't need a heat engine. There you get 90% efficiency even with heating oil.
  - CydeWeys 8y ago
    If you need heating, the efficiency of an electricity-powered heat pump is around 300%, so batteries are actually competitive here.
- leetcrew 8y ago
  diesel engines can exceed 45% efficiency [0], so lithium ion would have to more than triple in energy density to be competitive (using GP's numbers). that said, diesel is mainly used in large trucks and shipping vessels, where I would imagine energy per unit volume would be more important than energy per unit mass. if electricity were much cheaper than diesel fuel, it could certainly become the economic choice for all but the longest routes. [0] https://en.wikipedia.org/wiki/Diesel_engine#Major_advantages https://en.wikipedia.org/wiki/Diesel_engine#Major_advantages
  - erikpukinskis 8y ago
    Regenerative breaking could theoretically get you 2x.
    - CydeWeys 8y ago
      Regenerative braking gets you basically nothing on long steady-speed routes. Energy leaves the system primarily through air resistance and to a lesser degree mechanical and rolling resistance. Trucks crossing the country can go 60mph on cruise control for hours on end. Regenerative braking helps more for stop-and-go driving in cities but it's basically meaningless for long-haul trucking or shipping.
      - erikpukinskis 8y ago
        It also gets you something where there is altitude gain.
    - dredmorbius 8y ago
      In practice, a few percent, <10% AFAIR.
sdenton4 8y ago
Via Wikipedia: "Modern gasoline engines have a maximum thermal efficiency of about 25% to 50% when used to power a car." Meanwhile, the average passenger car in 2000 created 11,000 pounds of co2 over the course of a year... I don't think I had seen that number before - no wonder there's a problem. https://en.m.wikipedia.org/wiki/Exhaust_gas https://en.m.wikipedia.org/wiki/Exhaust_gas

CydeWeys 8y ago

If you can't actually extract it (because of limitations like Carnot efficiency, etc.), does it actually count? What's the real figure for usable energy in diesel?

maxerickson 8y ago
Depends on what you are doing. An awful lot of energy consumption is just fine with waste heat, it doesn't need a heat engine. There you get 90% efficiency even with heating oil.
- CydeWeys 8y ago
  If you need heating, the efficiency of an electricity-powered heat pump is around 300%, so batteries are actually competitive here.
leetcrew 8y ago
diesel engines can exceed 45% efficiency [0], so lithium ion would have to more than triple in energy density to be competitive (using GP's numbers). that said, diesel is mainly used in large trucks and shipping vessels, where I would imagine energy per unit volume would be more important than energy per unit mass. if electricity were much cheaper than diesel fuel, it could certainly become the economic choice for all but the longest routes. [0] https://en.wikipedia.org/wiki/Diesel_engine#Major_advantages https://en.wikipedia.org/wiki/Diesel_engine#Major_advantages
- erikpukinskis 8y ago
  Regenerative breaking could theoretically get you 2x.
  - CydeWeys 8y ago
    Regenerative braking gets you basically nothing on long steady-speed routes. Energy leaves the system primarily through air resistance and to a lesser degree mechanical and rolling resistance. Trucks crossing the country can go 60mph on cruise control for hours on end. Regenerative braking helps more for stop-and-go driving in cities but it's basically meaningless for long-haul trucking or shipping.
    - erikpukinskis 8y ago
      It also gets you something where there is altitude gain.
  - dredmorbius 8y ago
    In practice, a few percent, <10% AFAIR.

sdenton4 8y ago

Via Wikipedia: "Modern gasoline engines have a maximum thermal efficiency of about 25% to 50% when used to power a car." Meanwhile, the average passenger car in 2000 created 11,000 pounds of co2 over the course of a year... I don't think I had seen that number before - no wonder there's a problem. https://en.m.wikipedia.org/wiki/Exhaust_gas https://en.m.wikipedia.org/wiki/Exhaust_gas