5 ms·

If one looks at the Wh/kg of the very best li ion batteries right now (about 250Wh/kg) and then compares it to the Wh/kg in avgas or jet a or diesel, it's nuts.

If one looks at the Wh/kg of the very best li ion batteries right now (about 250Wh/kg) and then compares it to the Wh/kg in avgas or jet a or diesel, it's nuts. Even if you lose 40-60% to waste heat. The amount of energy contained in those fuels is ridiculously dense by comparison.

winter_blue 5y ago
It looks like diesel holds ~10,700 Wh/kg[1]. That’s over 40 times the volumetric energy density. I hope people find an electrical energy storage system (ie a battery) that’s cheap, and with high mass and volumetric energy density, soon. That would be huge for solving the impending climate (and pollution) crisis. [1] https://en.m.wikipedia.org/wiki/Energy_density#In_chemical_reactions_(oxidation) https://en.m.wikipedia.org/wiki/Energy_density#In_chemical_r...
- SigmundA 5y ago
  You must account for all the equipment to convert fuel into mechanical work as well. A battery is a large part of the equipment to covert electrons into useful electricity and electric motors and controller are comparatively light weight. Energy density is still higher I have done rough calculations that say batteries need to be at about 2000 wh/kg to be at parity with a diesel semi and the theoretic upper limit for lithium is 2600 wh/kg.
mgoetzke 5y ago
And the energy stored in it does not need to be paid :) That is why these companies make so much money of course.
- ganafagol 5y ago
  Oil is free? Not sure where the Saudis got there riches from then. Otoh sitting in the sun for a few hours to charge some battery via rays from the sun is itself free.
  - tohmasu 5y ago
    >Otoh sitting in the sun for a few hours to charge some battery via rays from the sun is itself free. Sounds wonderful, please show the math.
leoedin 5y ago
Not only that, hydrocarbon fuels also disappear after use - meaning you get another massive boost from the weight dropping over time, as the energy required by an aircraft to cruise is partially dependent on it's weight. So the energy density of batteries is effectively even lower than on face value.
SigmundA 5y ago
You must also account for the engine / motor / transmission / drivetrain / fuel tank weight difference you can't just look at fuel weight alone. In ground vehicles the weight of the engine and transmission and running gear is more than an electric motor and controller with much simpler usually single speed transmission and drivetrain especially diesel. Then there is structural batteries where the structure of battery helps replace some of the vehicle structure reducing wieght. This is why electric cars are starting to be competitive. Planes are somewhat different modern turbine engines are relatively light for their power output and there is not much of a transmission on planes, usually variable props instead and fuel tanks are sort of structural. Although having many multiple props driven by small electric motors can have advantages which would be complicated and heavy to do with a drivetrain in a plane. Still electric planes are far from practical IMO.

winter_blue 5y ago

It looks like diesel holds ~10,700 Wh/kg[1]. That’s over 40 times the volumetric energy density. I hope people find an electrical energy storage system (ie a battery) that’s cheap, and with high mass and volumetric energy density, soon. That would be huge for solving the impending climate (and pollution) crisis. [1] https://en.m.wikipedia.org/wiki/Energy_density#In_chemical_reactions_(oxidation) https://en.m.wikipedia.org/wiki/Energy_density#In_chemical_r...

SigmundA 5y ago
You must account for all the equipment to convert fuel into mechanical work as well. A battery is a large part of the equipment to covert electrons into useful electricity and electric motors and controller are comparatively light weight. Energy density is still higher I have done rough calculations that say batteries need to be at about 2000 wh/kg to be at parity with a diesel semi and the theoretic upper limit for lithium is 2600 wh/kg.

mgoetzke 5y ago

And the energy stored in it does not need to be paid :) That is why these companies make so much money of course.

ganafagol 5y ago
Oil is free? Not sure where the Saudis got there riches from then. Otoh sitting in the sun for a few hours to charge some battery via rays from the sun is itself free.
- tohmasu 5y ago
  >Otoh sitting in the sun for a few hours to charge some battery via rays from the sun is itself free. Sounds wonderful, please show the math.

leoedin 5y ago

Not only that, hydrocarbon fuels also disappear after use - meaning you get another massive boost from the weight dropping over time, as the energy required by an aircraft to cruise is partially dependent on it's weight. So the energy density of batteries is effectively even lower than on face value.

SigmundA 5y ago

You must also account for the engine / motor / transmission / drivetrain / fuel tank weight difference you can't just look at fuel weight alone. In ground vehicles the weight of the engine and transmission and running gear is more than an electric motor and controller with much simpler usually single speed transmission and drivetrain especially diesel. Then there is structural batteries where the structure of battery helps replace some of the vehicle structure reducing wieght. This is why electric cars are starting to be competitive. Planes are somewhat different modern turbine engines are relatively light for their power output and there is not much of a transmission on planes, usually variable props instead and fuel tanks are sort of structural. Although having many multiple props driven by small electric motors can have advantages which would be complicated and heavy to do with a drivetrain in a plane. Still electric planes are far from practical IMO.