6 ms·

Yep, battery energy density is still far off from fossil fuels. This is from 2012 but still relevant and why we don’t have electric commercial passenger planes

Yep, battery energy density is still far off from fossil fuels. This is from 2012 but still relevant and why we don’t have electric commercial passenger planes, and probably never will until we make 10x gains in energy density: “”” Stored energy in fuel is considerable: gasoline is the champion at 47.5 MJ/kg and 34.6 MJ/liter; the gasoline in a fully fueled car has the same energy content as a thousand sticks of dynamite. A lithium-ion battery pack has about 0.3 MJ/kg and about 0.4 MJ/liter (Chevy VOLT). Gasoline thus has about 100 times the energy density of a lithium-ion battery. This difference in energy density is partially mitigated by the very high efficiency of an electric motor in converting energy stored in the battery to making the car move: it is typically 60-80 percent efficient. The efficiency of an internal combustion engine in converting the energy stored in gasoline to making the car move is typically 15 percent (EPA 2012). With the ratio about 5, a battery with an energy storage density 1/5 of that of gasoline would have the same range as a gasoline-powered car. We are not even close to this at present. “”” https://www.aps.org/publications/apsnews/201208/backpage.cfm https://www.aps.org/publications/apsnews/201208/backpage.cfm

epistasis 5y ago
While I agree about aviation, rail is an entirely different problem, and big heavy things move great. For freight in the US, the worst case segment I know about is ~700 miles. This can be handled with about 400-500 feet of battery cars, which is probably 5%-10% of train length. So the worst possible scenario is pretty close to feasibility with current tech. If railroads were to start investing in this level of battery, beyond saving a lot of fuel costs, they'd have a couple hundred MWh of battery at every rail station. This would be a significant grid asset, at least at the moment. In a decade, that level of storage is probably going to be extremely common. But in any case, there's significant opportunity for demand response payments, if not using the batteries for replacing peaking power on the grid.
- Seattle3503 5y ago
  Given the efficiency of rail, is fuel even a considerable part of their costs?
  - epistasis 5y ago
    I don't know, actually! So some napkin math... Rail is 2% of transportation emissions, which is 29% of total US emissions [1], which was 6.558e6 metric tons in 2019 [2]. So rail is 3.8e7 kg of CO2 emissions. Diesel emits 10 kg/gallon [3], so that's 3.8e6 gallons, and at a cost of $3/gallon that's only $10M dollars out of what is an $80B industry [4]. That's so vanishingly small that I wonder if I have done something wrong here... [1] https://www.epa.gov/greenvehicles/fast-facts-transportation-greenhouse-gas-emissions https://www.epa.gov/greenvehicles/fast-facts-transportation-... [2] https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas... [3] https://www.epa.gov/energy/greenhouse-gases-equivalencies-calculator-calculations-and-references https://www.epa.gov/energy/greenhouse-gases-equivalencies-ca... [4] https://railroads.dot.gov/rail-network-development/freight-rail-overview https://railroads.dot.gov/rail-network-development/freight-r...
    - epistasis 5y ago
      My mistake: the starting amount of CO2 is low by a factor of 1000, and therefore fuel costs are around $10B of the $80B industry. That's in line with my initial expectations, and cutting fuel costs by even, say, 30% could be a big win.
atlasunshrugged 5y ago
Part of the issue is not just the density of the fuel but also the fact that the weight remains the same no matter how much of it you use. With gasoline/coal/etc. when you use the product it then decreases the weight of the amount of fuel stored, you don't get that loss with batteries so while you get "additional" gains with e.g. aviation fuel the further you are along your trip and the more you've burned, you don't get that with batteries.
- snovv_crash 5y ago
  That's an issue for planes, but I'm not sure the weight of the fuel decrease is really noticeable in a locomotive as a percentage of total tonnage.
nradov 5y ago
Eviation is about to start testing a prototype small electric commercial passenger airplane. It will only be suitable for short flights with a few passengers, and it's not clear whether the economics will work out. https://www.flyingmag.com/alice-electric-commuter-airplane-prototype-spotted-on-the-runway/ https://www.flyingmag.com/alice-electric-commuter-airplane-p... For larger airliners there could eventually be a role for plug-in hybrid propulsion systems. Use a fairly small battery pack and electric motors to augment the turbines during take-off and climb, then switch them off during cruise. There would be a weight penalty but it might deliver a net fuel savings for shorter flights.
- torginus 5y ago
  They won't. If you ever flew in these small aircraft, you know that they are extremely susceptible to weather conditions, and can be easily grounded due to rain, snow, strong winds or extremely hot weather. Even ignoring the heavy batteries giving them range that's barely acceptable, you'd still need to pay pilot's salaries per every few passenger, a major cost even when divided between the far larger amount of people flying on an airliner.

epistasis 5y ago

While I agree about aviation, rail is an entirely different problem, and big heavy things move great. For freight in the US, the worst case segment I know about is ~700 miles. This can be handled with about 400-500 feet of battery cars, which is probably 5%-10% of train length. So the worst possible scenario is pretty close to feasibility with current tech. If railroads were to start investing in this level of battery, beyond saving a lot of fuel costs, they'd have a couple hundred MWh of battery at every rail station. This would be a significant grid asset, at least at the moment. In a decade, that level of storage is probably going to be extremely common. But in any case, there's significant opportunity for demand response payments, if not using the batteries for replacing peaking power on the grid.

Seattle3503 5y ago
Given the efficiency of rail, is fuel even a considerable part of their costs?
- epistasis 5y ago
  I don't know, actually! So some napkin math... Rail is 2% of transportation emissions, which is 29% of total US emissions [1], which was 6.558e6 metric tons in 2019 [2]. So rail is 3.8e7 kg of CO2 emissions. Diesel emits 10 kg/gallon [3], so that's 3.8e6 gallons, and at a cost of $3/gallon that's only $10M dollars out of what is an $80B industry [4]. That's so vanishingly small that I wonder if I have done something wrong here... [1] https://www.epa.gov/greenvehicles/fast-facts-transportation-greenhouse-gas-emissions https://www.epa.gov/greenvehicles/fast-facts-transportation-... [2] https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas... [3] https://www.epa.gov/energy/greenhouse-gases-equivalencies-calculator-calculations-and-references https://www.epa.gov/energy/greenhouse-gases-equivalencies-ca... [4] https://railroads.dot.gov/rail-network-development/freight-rail-overview https://railroads.dot.gov/rail-network-development/freight-r...
  - epistasis 5y ago
    My mistake: the starting amount of CO2 is low by a factor of 1000, and therefore fuel costs are around $10B of the $80B industry. That's in line with my initial expectations, and cutting fuel costs by even, say, 30% could be a big win.

atlasunshrugged 5y ago

Part of the issue is not just the density of the fuel but also the fact that the weight remains the same no matter how much of it you use. With gasoline/coal/etc. when you use the product it then decreases the weight of the amount of fuel stored, you don't get that loss with batteries so while you get "additional" gains with e.g. aviation fuel the further you are along your trip and the more you've burned, you don't get that with batteries.

snovv_crash 5y ago
That's an issue for planes, but I'm not sure the weight of the fuel decrease is really noticeable in a locomotive as a percentage of total tonnage.

nradov 5y ago

Eviation is about to start testing a prototype small electric commercial passenger airplane. It will only be suitable for short flights with a few passengers, and it's not clear whether the economics will work out. https://www.flyingmag.com/alice-electric-commuter-airplane-prototype-spotted-on-the-runway/ https://www.flyingmag.com/alice-electric-commuter-airplane-p... For larger airliners there could eventually be a role for plug-in hybrid propulsion systems. Use a fairly small battery pack and electric motors to augment the turbines during take-off and climb, then switch them off during cruise. There would be a weight penalty but it might deliver a net fuel savings for shorter flights.

torginus 5y ago
They won't. If you ever flew in these small aircraft, you know that they are extremely susceptible to weather conditions, and can be easily grounded due to rain, snow, strong winds or extremely hot weather. Even ignoring the heavy batteries giving them range that's barely acceptable, you'd still need to pay pilot's salaries per every few passenger, a major cost even when divided between the far larger amount of people flying on an airliner.