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Even with the increased electrification of transport, there's still a very strong case for liquid fuel - it just offers an energy density so much higher than ba

Even with the increased electrification of transport, there's still a very strong case for liquid fuel - it just offers an energy density so much higher than batteries, especially in off-grid or remote situations. Electric drivetrains open up an interesting potential for range-extenders which charge the batteries. The constraints are different than conventional engines - lower peak power, more-or-less continuous power output operation, no sudden torque changes. Different constraints generally mean a different optimal solution.

henearkr 6y ago
There is not a huge gap at all. Li-metal batteries [edit: still an immature tech] are at around 14 MJ / kg, and gasoline is at 47.5 MJ / kg. Moreover, suppose that you are really "off-grid". Meaning, you are off any fuel supply network!! In this case precisely, you would be saved by electric-related techs, such as photovoltaic.
- leoedin 6y ago
  I was using off-grid in the most straightforward of senses - off the electricity grid. That doesn't necessary mean stationary or without weight limits (as solar would require) - it could mean long distance trucking, or logging, construction, or even the maintenance of electricity pylons (which probably can't be turned on during that process). All those require huge amounts of energy, and batteries are not yet nearly there (as others point out, your numbers for battery energy density are out by a factor of 30).
- avhon1 6y ago
  Or saved by combustion-related techs, such as biofuel, biogass, wood gas, or just plain-old "burn organic matter".
  - henearkr 6y ago
    But, using electric, I just have to charge it by plugging in a solar panel. With existing OTS products. If I want to burn dead leaves to run my car... well that sucks right now (moreover that isn't anymore 0 emission).
    - avhon1 6y ago
      You can turn that around just as easily. If I run off to start a farm, and I buy an existing OTS used tractor, it will have a tank that I can pour almost any flammable liquid into to make it run. If I want to plug the tractor in... well, that'll get the engine to turn over, but it won't get it moving anywhere. If I build myself a cabin in the woods, I can burn wood or wood pellets to keep cook food, or keep warm during the winter. Alternatively, I could purchase batteries, PV panels, and the necessary charge control electronics, in order to run an electric heater. Burning recently-alive biomass does release carbon, but it's carbon that was in the atmosphere as recently as a few months ago. It isn't zero emission, but it doesn't contribute a long-term increase to the amount of carbon in the atmosphere.
      - deleted 6y ago
        [deleted]
      - 7952 6y ago
        Other emissions like particulates can be worse from wood burning. And most of the CO2 is likely to have been collected over a much longer period than a few months. Without a significant tree planting effort it is likely to increase CO2 levels.
    - deleted 6y ago
      [deleted]
    - jacquesm 6y ago
      Burning dead leaves actually does count as carbon neutral. The balance is whether you burn fossil fuels, not whether or not you burn anything at all.
      - henearkr 6y ago
        No, this does not work. A forest is a carbon store. Burning trees puts carbon from this store to the atmosphere. To count it as carbon neutral is an accounting mistake, that could be very costly... Burn the dead leaves and you shrink humus (or annihilate it, depending on how much you do it), another huge carbon store. So that makes it yet another accounting mistake. More generally, it is good practice to separate well atmospheric carbon (CO2) and captive carbone (anything in solid/liquid state). Just show that faithfully in the accounting method, and a lot of good will follow.
- burmanm 6y ago
  Yes, photovoltaics during winter are a dream. "Charging next time in 6 months".
  - henearkr 6y ago
    Not at all, except if you mean arctic winter (when it's technically night all the day). Also, electric offers you the plethora of choices in methods to produce your energy. If it's not photovoltaic, you still have many solutions. Could as well be eolian, or a dam, or hundred of people riding generator-bikes (half-kidding), or etc.
    - 34679 6y ago
      >hundred of people riding generator-bikes (half-kidding) I've wondered if it makes sense for gyms to be paying for electricity.
      - henearkr 6y ago
        Also, what about energy-producing gym equipment in airliners? Free energy (but maybe only an epsilon), and no more deep vein thrombosis!!
      - bananabreakfast 6y ago
        It's funny to think about, but if you do the math even dozens of humans riding bikes contribute so little energy compared to what a building requires it is totally negligible and would never be worth the cost beyond a gimmick.
  - avhon1 6y ago
    It's not quite that bad. Solar panels that point directly at the sun during the summer solstice will still receive 91% the density of light during the winter solstice. ( cos(24deg) ~= 0.91 ) Where I live (about 40deg north), the winter solstice is 63% as long (9.5 hours) as the summer solstice (15 hours). Even a thick blanket of snow, or 100% cloud cover, will only reduce power by about 50%. --- Under the worst possible conditions (not considering temperature), on the shortest day of the year, with 100% clouds and a thick layer of snow, PV panels would produce 14% as much power per day as on the longest day of the year with 0 cloud cover.
- AnonC 6y ago
  > There is not a huge gap at all. > Li-metal batteries top at around 14 MJ / kg, and gasoline is at 47.5 MJ / kg. Wouldn’t this gap actually be very close considering that the efficiency of an ICE on gasoline is what, 30-40% at best (IIRC)?
  - avhon1 6y ago
    It depends. Electric motors also have losses in their controllers, which removes another 5% or 10%. If you want mechanical power output and have 1kg of pre-charged batteries and 1kg of liquid fuel, the efficiency of electric motors might close the density gap. Lets assume 95% efficient controller+motor (slightly optimistic) and 30% efficient ICE (somewhat pessimistic). 1kg * 14 MJ/kg * 95% = 13 MJ mechanical 1kg * 47 MJ/kg * 30% = 14 MJ mechanical It comes out pretty close! If you want mechanical power and also heat (for keeping people, animals, or equipment warm, decreasing the viscosity of fluids, etc), ICE is definitely the way to go. -- edit -- /u/ash points out Tesla's energy density is is 0.576 MJ/kg 1kg * 0.58 MJ/kg * 95% = 0.55 MJ mechanical ...not even slightly close.
    - varjag 6y ago
      You should factor in regenerative braking of EVs, which is lost as heat for fossils vehicles.
      - petre 6y ago
        One can't really charge a battery with power spikes from randomly hitting the brakes. Only part of the braking energy is recoverable, for example when braking to reduce speed while descending a long slope. Braking strategy should also be different in this case: similar to engine braking in regular vehicles. Since most EVs rarely have a multi speed gearbox, regenerative braking should be built into the brake pedal.
        NeutronStar 6y ago
        Regenerative braking is built into releasing the gas pedal.
- ash 6y ago
  > Li-metal batteries top at around 14 MJ / kg Do you have a link to back this number? Are these batteries rechargeable? Does the measurement include wiring, cooling, cell connections and overall structure of the battery pack? For comparison, Tesla's (Li-ion) battery pack energy density is 160 Wh/kg, which is 0.576 MJ/kg: https://www.pv-magazine.com/2020/02/11/energy-density-advances-and-faster-charging-would-unlock-ev-revolution/ https://www.pv-magazine.com/2020/02/11/energy-density-advanc...
  - henearkr 6y ago
    I used that, and actually I may have missed the bit where they explain that "lithium metal as an anode were suggested for future high-energy-density batteries", implying that it's still an immature tech. https://pubs.rsc.org/en/content/articlelanding/2019/ee/c9ee00716d#!divAbstract https://pubs.rsc.org/en/content/articlelanding/2019/ee/c9ee0...
  - readams 6y ago
    At that point you need to consider the whole car. The engine needed to extract energy from that fuel is much bigger in the ICE car. And it also needs cooling, etc. Comparing just the gas tank to several subsystems of a battery electric vehicle is not really an interesting comparison. The closest comparison at that level is just gas vs just cells. Overall electric is still lower energy density per weight, but is also far more efficient. The whole Tesla pack has the energy of just a couple gallons of gas but can go 400 miles.
- sokoloff 6y ago
  Airliners are off-grid while in use but fly from fuel supply to fuel supply. They are also quite weight sensitive, requiring additional induced drag to be overcome at heavier weights.
- lizknope 6y ago
  I have driven through parts of the western US where it is 100 miles to the next gas/petrol station. There are farms and ranches in these areas but they are connected to the electrical grid with wires. It seems like having an electric tractor and charging at the farm would be more convenient than transporting hundreds of gallons of diesel fuel from 100 miles away.
  - Vvector 6y ago
    Tractors are bursty. They are heavily used at planting and harvesting. Farmers can't spend long periods of time recharging in the middle of planting season. And it would be too expensive to buy 12 hours of battery capacity for a couple times a year. Gas still wins with a short refuel time.
    - supportlocal4h 6y ago
      Actually, batteries win on refuel time. Swapping batteries is much faster than filling a tank. Gas wins on meantime between refuels and in other categories. Farmers can and happily will spend super long periods of time recharging if they can operate during the recharge. My own initial experiences have been mixed. Overall advantage still goes to gas. But I think we're very close to getting this battery thing figured out. Just a few years away. When we look back it will seem like it happened overnight.
      - gambiting 6y ago
        >>Actually, batteries win on refuel time. Swapping batteries is much faster than filling a tank By that logic, you could say that there is absolutely no difference, because if you can imagine a car where the battery can be swapped, you should be able to imagine a car where the entire fuel tank is swapped. A tractor arrives at a station, and instead of filling up 500 litres of diesel, the entire tank is simply replaced with a full one. It wins again since fuel tanks are cheap - they are just metal and plastic after all, you can have several just sitting there, full or empty. The fact that no one has done it yet suggests that this really isn't an issue - commercial diesel filling stations usually run at much higher pressure than your regular pumps, a truck/tractor tank fills in minutes because of a much higher flow rate.
- jlg23 6y ago
  > Moreover, suppose that you are really "off-grid". Meaning, you are off any fuel supply network!! In this case precisely, you would be saved by electric-related techs, such as photovoltaic. Albeit in theory true, here in the outskirts of the Sahara, I have yet to find a village where I can get an electrician to fix my solar panels, though a few bottles of gasoline can be found everywhere.
- 0xffff2 6y ago
  >edit: still an immature tech If there was a Nobel Prize for understatement, this comment would take it hands down. New "breakthroughs" in battery energy density are a dime a dozen. They're proving incredibly difficult to bring to commercial viability, and there's no evidence that that's going to change.
  - henearkr 6y ago
    Thanks I'm very honored.
- Hypx 6y ago
  Hydrogen tops out at 142 MJ / kg. Disappointing that so few here are aware of this basic fact. It seems obvious that if you want the density of liquid fuels, hydrogen is the answer. Compromising yourself with a lower energy density substance stands as a very difficult problem to solve.
Brakenshire 6y ago
I’m surprised there hasn’t been more development of engines optimized as range extenders. That seemed like an obvious next step from the Prius, for example. But I think the peak of that opportunity has passed. The market in Europe and China is going to flip to pure electric in 5-8 years, with the US 5 years later. The window for developing new models that fit into that transition is shrinking. There will be long term demand for range extended vehicles, still in 15 or 20 years, but it will be niche.
- ChuckNorris89 6y ago
  >The market in Europe and China is going to flip to pure electric in 5-8 years That's way too optimistic for Europe. Maybe with the exception of Norway and Europe's largest metros like London, most of Europe will stay on ICE for a long time. The price of electric cars here is too high for most incomes and the cheaper ones have too little range compared to ICEs. Not to mention the charging infrastructure is still lacking. Right now they're still toys for the rich man with a house and not tools for the average joe. I'd rather we invest the money in public transport and cycling infrastructure to rid the cities of cars but unfortunately the auto industry lobbies too strong in Europe for that to happen.
  - scrumbledober 6y ago
    I'm also just really not sure the battery capacity will be able to scale that quickly. As it stands we are basically making EVs as fast as we make batteries.
  - Retric 6y ago
    Electric cars are going to become extremely compelling very soon. A 300 mile electric car is close to the same cost as an IC engine over it’s lifespan. But, where IC engines have a hundred years of development and economies of scale electric cars are getting significantly better very quickly. Charge infrastructure is expanding rapidly due to current rates of adoption which further makes electric cars more appealing every year.
    - 6y ago
grecy 6y ago
While it's true that liquid fuel is more energy dense than batteries, you have to remember that most Internal Combustion Engines are only around 20% efficient. So even though you're carrying around a huge amount of potential energy in the form of gasoline, your engine can only covert about 20% of that into motion.
m-p-3 6y ago
And it's hard to deny one advantage of combustible against batteries. The weight of combustible tank goes down as it become empty, while a battery weight remains constant. This must have a huge decisional impact when manufacturing aircrafts.

henearkr 6y ago

There is not a huge gap at all. Li-metal batteries [edit: still an immature tech] are at around 14 MJ / kg, and gasoline is at 47.5 MJ / kg. Moreover, suppose that you are really "off-grid". Meaning, you are off any fuel supply network!! In this case precisely, you would be saved by electric-related techs, such as photovoltaic.

leoedin 6y ago
I was using off-grid in the most straightforward of senses - off the electricity grid. That doesn't necessary mean stationary or without weight limits (as solar would require) - it could mean long distance trucking, or logging, construction, or even the maintenance of electricity pylons (which probably can't be turned on during that process). All those require huge amounts of energy, and batteries are not yet nearly there (as others point out, your numbers for battery energy density are out by a factor of 30).
avhon1 6y ago
Or saved by combustion-related techs, such as biofuel, biogass, wood gas, or just plain-old "burn organic matter".
- henearkr 6y ago
  But, using electric, I just have to charge it by plugging in a solar panel. With existing OTS products. If I want to burn dead leaves to run my car... well that sucks right now (moreover that isn't anymore 0 emission).
  - avhon1 6y ago
    You can turn that around just as easily. If I run off to start a farm, and I buy an existing OTS used tractor, it will have a tank that I can pour almost any flammable liquid into to make it run. If I want to plug the tractor in... well, that'll get the engine to turn over, but it won't get it moving anywhere. If I build myself a cabin in the woods, I can burn wood or wood pellets to keep cook food, or keep warm during the winter. Alternatively, I could purchase batteries, PV panels, and the necessary charge control electronics, in order to run an electric heater. Burning recently-alive biomass does release carbon, but it's carbon that was in the atmosphere as recently as a few months ago. It isn't zero emission, but it doesn't contribute a long-term increase to the amount of carbon in the atmosphere.
    - deleted 6y ago
      [deleted]
    - 7952 6y ago
      Other emissions like particulates can be worse from wood burning. And most of the CO2 is likely to have been collected over a much longer period than a few months. Without a significant tree planting effort it is likely to increase CO2 levels.
  - deleted 6y ago
    [deleted]
  - jacquesm 6y ago
    Burning dead leaves actually does count as carbon neutral. The balance is whether you burn fossil fuels, not whether or not you burn anything at all.
    - henearkr 6y ago
      No, this does not work. A forest is a carbon store. Burning trees puts carbon from this store to the atmosphere. To count it as carbon neutral is an accounting mistake, that could be very costly... Burn the dead leaves and you shrink humus (or annihilate it, depending on how much you do it), another huge carbon store. So that makes it yet another accounting mistake. More generally, it is good practice to separate well atmospheric carbon (CO2) and captive carbone (anything in solid/liquid state). Just show that faithfully in the accounting method, and a lot of good will follow.
burmanm 6y ago
Yes, photovoltaics during winter are a dream. "Charging next time in 6 months".
- henearkr 6y ago
  Not at all, except if you mean arctic winter (when it's technically night all the day). Also, electric offers you the plethora of choices in methods to produce your energy. If it's not photovoltaic, you still have many solutions. Could as well be eolian, or a dam, or hundred of people riding generator-bikes (half-kidding), or etc.
  - 34679 6y ago
    >hundred of people riding generator-bikes (half-kidding) I've wondered if it makes sense for gyms to be paying for electricity.
    - henearkr 6y ago
      Also, what about energy-producing gym equipment in airliners? Free energy (but maybe only an epsilon), and no more deep vein thrombosis!!
    - bananabreakfast 6y ago
      It's funny to think about, but if you do the math even dozens of humans riding bikes contribute so little energy compared to what a building requires it is totally negligible and would never be worth the cost beyond a gimmick.
- avhon1 6y ago
  It's not quite that bad. Solar panels that point directly at the sun during the summer solstice will still receive 91% the density of light during the winter solstice. ( cos(24deg) ~= 0.91 ) Where I live (about 40deg north), the winter solstice is 63% as long (9.5 hours) as the summer solstice (15 hours). Even a thick blanket of snow, or 100% cloud cover, will only reduce power by about 50%. --- Under the worst possible conditions (not considering temperature), on the shortest day of the year, with 100% clouds and a thick layer of snow, PV panels would produce 14% as much power per day as on the longest day of the year with 0 cloud cover.
AnonC 6y ago
> There is not a huge gap at all. > Li-metal batteries top at around 14 MJ / kg, and gasoline is at 47.5 MJ / kg. Wouldn’t this gap actually be very close considering that the efficiency of an ICE on gasoline is what, 30-40% at best (IIRC)?
- avhon1 6y ago
  It depends. Electric motors also have losses in their controllers, which removes another 5% or 10%. If you want mechanical power output and have 1kg of pre-charged batteries and 1kg of liquid fuel, the efficiency of electric motors might close the density gap. Lets assume 95% efficient controller+motor (slightly optimistic) and 30% efficient ICE (somewhat pessimistic). 1kg * 14 MJ/kg * 95% = 13 MJ mechanical 1kg * 47 MJ/kg * 30% = 14 MJ mechanical It comes out pretty close! If you want mechanical power and also heat (for keeping people, animals, or equipment warm, decreasing the viscosity of fluids, etc), ICE is definitely the way to go. -- edit -- /u/ash points out Tesla's energy density is is 0.576 MJ/kg 1kg * 0.58 MJ/kg * 95% = 0.55 MJ mechanical ...not even slightly close.
  - varjag 6y ago
    You should factor in regenerative braking of EVs, which is lost as heat for fossils vehicles.
    - petre 6y ago
      One can't really charge a battery with power spikes from randomly hitting the brakes. Only part of the braking energy is recoverable, for example when braking to reduce speed while descending a long slope. Braking strategy should also be different in this case: similar to engine braking in regular vehicles. Since most EVs rarely have a multi speed gearbox, regenerative braking should be built into the brake pedal.
      - NeutronStar 6y ago
        Regenerative braking is built into releasing the gas pedal.
ash 6y ago
> Li-metal batteries top at around 14 MJ / kg Do you have a link to back this number? Are these batteries rechargeable? Does the measurement include wiring, cooling, cell connections and overall structure of the battery pack? For comparison, Tesla's (Li-ion) battery pack energy density is 160 Wh/kg, which is 0.576 MJ/kg: https://www.pv-magazine.com/2020/02/11/energy-density-advances-and-faster-charging-would-unlock-ev-revolution/ https://www.pv-magazine.com/2020/02/11/energy-density-advanc...
- henearkr 6y ago
  I used that, and actually I may have missed the bit where they explain that "lithium metal as an anode were suggested for future high-energy-density batteries", implying that it's still an immature tech. https://pubs.rsc.org/en/content/articlelanding/2019/ee/c9ee00716d#!divAbstract https://pubs.rsc.org/en/content/articlelanding/2019/ee/c9ee0...
- readams 6y ago
  At that point you need to consider the whole car. The engine needed to extract energy from that fuel is much bigger in the ICE car. And it also needs cooling, etc. Comparing just the gas tank to several subsystems of a battery electric vehicle is not really an interesting comparison. The closest comparison at that level is just gas vs just cells. Overall electric is still lower energy density per weight, but is also far more efficient. The whole Tesla pack has the energy of just a couple gallons of gas but can go 400 miles.
sokoloff 6y ago
Airliners are off-grid while in use but fly from fuel supply to fuel supply. They are also quite weight sensitive, requiring additional induced drag to be overcome at heavier weights.
lizknope 6y ago
I have driven through parts of the western US where it is 100 miles to the next gas/petrol station. There are farms and ranches in these areas but they are connected to the electrical grid with wires. It seems like having an electric tractor and charging at the farm would be more convenient than transporting hundreds of gallons of diesel fuel from 100 miles away.
- Vvector 6y ago
  Tractors are bursty. They are heavily used at planting and harvesting. Farmers can't spend long periods of time recharging in the middle of planting season. And it would be too expensive to buy 12 hours of battery capacity for a couple times a year. Gas still wins with a short refuel time.
  - supportlocal4h 6y ago
    Actually, batteries win on refuel time. Swapping batteries is much faster than filling a tank. Gas wins on meantime between refuels and in other categories. Farmers can and happily will spend super long periods of time recharging if they can operate during the recharge. My own initial experiences have been mixed. Overall advantage still goes to gas. But I think we're very close to getting this battery thing figured out. Just a few years away. When we look back it will seem like it happened overnight.
    - gambiting 6y ago
      >>Actually, batteries win on refuel time. Swapping batteries is much faster than filling a tank By that logic, you could say that there is absolutely no difference, because if you can imagine a car where the battery can be swapped, you should be able to imagine a car where the entire fuel tank is swapped. A tractor arrives at a station, and instead of filling up 500 litres of diesel, the entire tank is simply replaced with a full one. It wins again since fuel tanks are cheap - they are just metal and plastic after all, you can have several just sitting there, full or empty. The fact that no one has done it yet suggests that this really isn't an issue - commercial diesel filling stations usually run at much higher pressure than your regular pumps, a truck/tractor tank fills in minutes because of a much higher flow rate.
jlg23 6y ago
> Moreover, suppose that you are really "off-grid". Meaning, you are off any fuel supply network!! In this case precisely, you would be saved by electric-related techs, such as photovoltaic. Albeit in theory true, here in the outskirts of the Sahara, I have yet to find a village where I can get an electrician to fix my solar panels, though a few bottles of gasoline can be found everywhere.
0xffff2 6y ago
>edit: still an immature tech If there was a Nobel Prize for understatement, this comment would take it hands down. New "breakthroughs" in battery energy density are a dime a dozen. They're proving incredibly difficult to bring to commercial viability, and there's no evidence that that's going to change.
- henearkr 6y ago
  Thanks I'm very honored.
Hypx 6y ago
Hydrogen tops out at 142 MJ / kg. Disappointing that so few here are aware of this basic fact. It seems obvious that if you want the density of liquid fuels, hydrogen is the answer. Compromising yourself with a lower energy density substance stands as a very difficult problem to solve.

Brakenshire 6y ago

I’m surprised there hasn’t been more development of engines optimized as range extenders. That seemed like an obvious next step from the Prius, for example. But I think the peak of that opportunity has passed. The market in Europe and China is going to flip to pure electric in 5-8 years, with the US 5 years later. The window for developing new models that fit into that transition is shrinking. There will be long term demand for range extended vehicles, still in 15 or 20 years, but it will be niche.

ChuckNorris89 6y ago
>The market in Europe and China is going to flip to pure electric in 5-8 years That's way too optimistic for Europe. Maybe with the exception of Norway and Europe's largest metros like London, most of Europe will stay on ICE for a long time. The price of electric cars here is too high for most incomes and the cheaper ones have too little range compared to ICEs. Not to mention the charging infrastructure is still lacking. Right now they're still toys for the rich man with a house and not tools for the average joe. I'd rather we invest the money in public transport and cycling infrastructure to rid the cities of cars but unfortunately the auto industry lobbies too strong in Europe for that to happen.
- scrumbledober 6y ago
  I'm also just really not sure the battery capacity will be able to scale that quickly. As it stands we are basically making EVs as fast as we make batteries.
- Retric 6y ago
  Electric cars are going to become extremely compelling very soon. A 300 mile electric car is close to the same cost as an IC engine over it’s lifespan. But, where IC engines have a hundred years of development and economies of scale electric cars are getting significantly better very quickly. Charge infrastructure is expanding rapidly due to current rates of adoption which further makes electric cars more appealing every year.
  - 6y ago

grecy 6y ago

While it's true that liquid fuel is more energy dense than batteries, you have to remember that most Internal Combustion Engines are only around 20% efficient. So even though you're carrying around a huge amount of potential energy in the form of gasoline, your engine can only covert about 20% of that into motion.

m-p-3 6y ago

And it's hard to deny one advantage of combustible against batteries. The weight of combustible tank goes down as it become empty, while a battery weight remains constant. This must have a huge decisional impact when manufacturing aircrafts.