6 ms·

Electric aviation always strikes me as an odd idea, given the low power densities that batteries achieve. By contrast, biofuels are available today and can be

by svara 7y ago

Electric aviation always strikes me as an odd idea, given the low power densities that batteries achieve. By contrast, biofuels are available today and can be made from agricultural waste products (2nd gen), in bioreactors using salt water algae (3rd gen) or electrochemically (4th gen). They're potentially a drop in replacement for regular fuel - for planes, but also for cars. Due to the lower energy requirements for building ICE cars versus batteries, a biofuel powered car will be much better for CO2 emissions than an electric one, which you need to drive for many years before it beats a similar sized gasoline fueled car on sum CO2 emissions. So why are we not heavily investing in biofuel infrastructure? Why are electric motors and batteries hyped up as being the tech of the future? That's an honest question, since I've yet to hear a well-founded physical or engineering argument against it.

jeffreyrogers 7y ago
Don't biofuels take up way too much land to be economical? A large portion of US crop area is for corn and soybeans for ethanol and biodiesel. I can see the reasoning behind biofuels for aircraft, but I don't think biofuels are sustainable if people continue driving as much as they do now.
- JumpCrisscross 7y ago
  > Don't biofuels take up way too much land to be economical? Can we turn solar energy into hydrocarbons? (Water and CO2 are total feedstocks.)
  - philipkglass 7y ago
    Yes. Hydrogenate CO2 to methanol with electrolytic hydrogen produced from clean electricity [1]. Reform methanol to hydrocarbons [2] that can burn in existing engines. (Or burn methanol itself in slightly modified engines. This offers somewhat lower energy density per tankful of fuel, higher total efficiency from electricity-to-motion.) Synthetic fuel makes sense for fueling aircraft, rockets, long distance shipping, collectible historic cars, and other niches. It doesn't make sense for fueling everyday ground transportation. Too much of the original energy is lost in the chain of chemical transformations and the chemical processing requires facilities on the scale of conventional oil refineries. The total cost is lower to electrify ground transportation and supply it with clean electricity than to transform clean electricity into liquid fuels for equivalent legacy vehicles. [1] https://www.frontiersin.org/articles/10.3389/fchem.2018.00446/full https://www.frontiersin.org/articles/10.3389/fchem.2018.0044... [2] https://en.wikipedia.org/wiki/Gas_to_liquids https://en.wikipedia.org/wiki/Gas_to_liquids
    - JumpCrisscross 7y ago
      > Synthetic fuel makes sense for fueling aircraft, rockets, long distance shipping, collectible historic cars, and other niches What's driving the emphasis on lightweight batteries for aviation over better synthesisation?
      - philipkglass 7y ago
        For UAVs, battery/electric systems don't just reduce fueling costs. They deliver features unobtainable from hydrocarbon engines: - Extremely long flight endurance without refueling (in large solar/battery UAVs) - Low noise - Odorless - Simpler and cheaper manufacturing The advantages are much less obvious to me for aircraft that transport passengers or significant cargo loads. I suppose that the companies developing them are hoping to make the lifetime total cost of operation cheaper than existing aircraft serving the same niche. That seems much tougher to achieve. EDIT: Bye Aerospace, the company described in the IEEE article, says they are targeting a particular niche: https://byeaerospace.com/eflyer/ https://byeaerospace.com/eflyer/ They intend to replace trainer aircraft that burn leaded aviation gasoline. This polluting niche fuel costs significantly more than kerosene. Maybe the economics can work out for this case.
        JumpCrisscross 7y ago
        Thank you. Incredibly clarifying.
      - ajuc 7y ago
        There's no emphasis on lightweight batteries for passanger aircrafts, both batteries and biofuels are pursued and both are marginal compared to traditional fossil fuels.
throwawayhhakdl 7y ago
Biofuels always sounded wasteful to me. But this post makes a lot of good points on its merits that I hadn’t considered. How efficient is producing biofuels using renewable energy as a way of storing power long term?
nradov 7y ago
Alternatively, we can use electricity and heat from renewable power sources to synthesize kerosene from CO2 and water.
organsnyder 7y ago
For me, the experience of operating an electric vehicle is so much better than biofuels: refueling at home, simplicity of the drivetrain, and quietness/smoothness all are huge improvements over ICE vehicles. For your comparison between ICE and electric vehicles, are you counting the fuel processing and delivery infrastructure? Electric delivery infrastructure has very low emissions once it's in place, and production continues to get better (especially with distributed models like rooftop solar). Also, do you have a citation for "...lower energy requirements for building ICE cars versus batteries"? Yes, battery production is fairly intensive (economically and resource use), but (like I said above) the drivetrain is vastly simpler. I can't see how electric general aviation will become widespread without a monumental breakthrough. But it's hard to beat electric for ground-based transportation, IMHO.
- svara 7y ago
  This article addresses your questions: https://www.carbonbrief.org/factcheck-how-electric-vehicles-help-to-tackle-climate-change https://www.carbonbrief.org/factcheck-how-electric-vehicles-... Check out the "lifecycle greenhouse gas emissions" figures. It's really interesting in how it shows how different the total emissions are depending on which country you charge your electric car in. Also, depending on which electric car model you have, the lifecycle emission improvement over a conventional one might be relatively slim, depending on where and how much you drive it. By and large, electrics are at a substantial disadvantage due to both battery production and fuel cycle emissions, which then gets compensated over time as you drive the car. Edit: There's also this super interesting article on Wikipedia: https://en.wikipedia.org/wiki/Environmental_aspects_of_the_electric_car https://en.wikipedia.org/wiki/Environmental_aspects_of_the_e... which is largely consistent with the Carbonbrief article.
  - Tade0 7y ago
    I've seen the graph there and I find one thing troubling: Lifecycle greenhouse gas emissions for conventional and electric vehicles (by country) in grammes CO2-equivalent per kilometre, assuming 150,000 kilometres driven over the vehicle lifetime. That's less than 100,000 miles - rarely do cars travel less than that during their lifetime. Specifically in my country that would mean using the car for ~10 years, meanwhile the average passenger vehicle age is 14 years! As for biofuels: land and water usage are major hindrances. For example you need ~1800 liters of water to grow 1kg of soybean. Sure, you can use waste products for fuels, but they need to be waste from something.
maelito 7y ago
> Due to the lower energy requirements for building ICE cars versus batteries, a biofuel powered car will be much better for CO2 emissions than an electric one What's the GHG emissions for the different types of biofuels ? What's the land use needed ? How abundant ? Etc.
biggieshellz 7y ago
For general aviation (small prop planes), it's because so much of the cost of running one comes from the engine. The most common piston engines are supposed to make it 1500-2000 hours between overhauls, and an overhaul runs around $16K, so you have to save $10-15 per flight hour in engine reserve to pay for the overhaul when it comes due and to cover any unexpected maintenance between overhauls. Plus, there are consumables that aren't cheap -- oil changes, spark plugs, and so forth. A brushless electric motor has a lot fewer moving parts, and a lot less vibration, so overhauls could be cheaper and with a larger interval between them, and regular maintenance would be cheaper as well. Plus, no leaded avgas to mess with, no worries about reduced power at higher altitudes where the air is thinner, no worries about carburetor icing or adjusting the air/fuel mixture. Sounds like a win to me.
- TrueDuality 7y ago
  Unfortunately the reduced power is still a problem at higher altitudes but for different reasons. Instead of oxygen starvation, the props will have less to push against. This is still less of an issue as the electric motor can spin faster due to the reduced resistance. Higher speeds will create higher resistances from within the motor itself (which will in turn be increase the heat generated in the motor). That heat will also be harder to dissipate in lower pressures, but I suppose alternative cooling could be added as well.
  - dogma1138 7y ago
    I’m not entirely sure how you’ll cool the engines at high altitudes, combustion engines can use their exhaust to cool the engine. Using large radiators on an electric engine kinda defeats the purpose especially when they can’t be effectively be built into the body of the engine.
    - jandrese 7y ago
      I'm not sure why largeish passive radiators are a problem. If you're worried about the aesthetics you can put them inside of ducts and pass the air over them. This doesn't seem like it should be that big of an issue. Plus you'll probably want to recover some of that waste heat to heat the cabin.
the8472 7y ago
Combustion engines are quite inefficient and so are fuel synthesis processes. batteries have a high energy round-trip efficiency. The energy density does not matter as much in cars, which after mobile compute have been the primary drivers for technology. The density may make more sense for planes. Additionally 1st gen biofuels have poisoned the well to some extent due to competing with food crops.
throwawaycanada 7y ago
The only reason we have electric cars being pushed as much as they are is because of Tesla, specifically Elon Musk. It is not some government program. If it weren't for them we would have the Nissan Leaf and that is about it. And it wouldn't have half the performance that even it has today. Short answer: Monied interests don't really care, or don't think it is possible or feasible.
elihu 7y ago
Electric motors and batteries are very efficient, and therefore extremely cheap to operate. Biofuels make sense I think for aviation because you need that energy density to get a usable range, but the fuel is likely to be expensive for a long time. If you can figure out how to make liquid fuel for about fifty cents a gallon or so, it might be competitive with electricity for car use. I don't know what the energy requirements are for modern batteries, but I expect it varies a lot depending on battery chemistry. Battery sizes vary a lot, too.
nbanks 7y ago
For very short distance flights, electric aircraft are already viable. For example, Harbour Air Seaplanes operates a 20 minutes flight between Vancouver, BC and Victoria, BC. They use float planes because both cities are on the coast. Their first electric aircraft should take off in a couple months. One nice thing about electricity is that it's much cheaper than biofuels. This is because motors are much more efficient than engines, and because large generating stations are more efficient than small aircraft engines. BC is 95% hydroelectric which makes electricity even cheaper.
tim333 7y ago
>So why are we not heavily investing in biofuel infrastructure? I think the problems are more economics than physics. There was a huge investment in algal biofuels but it never proved economic. (eg https://www.greentechmedia.com/articles/read/lessons-from-the-great-algae-biofuel-bubble https://www.greentechmedia.com/articles/read/lessons-from-th...) I was a fan of Algenol for a while who were supposed to have algae that gave off ethanol cheaper than normal fossil fuel but it never worked out. Maybe something like that in the future will work.

by svara 7y ago

jeffreyrogers 7y ago

Don't biofuels take up way too much land to be economical? A large portion of US crop area is for corn and soybeans for ethanol and biodiesel. I can see the reasoning behind biofuels for aircraft, but I don't think biofuels are sustainable if people continue driving as much as they do now.

JumpCrisscross 7y ago
> Don't biofuels take up way too much land to be economical? Can we turn solar energy into hydrocarbons? (Water and CO2 are total feedstocks.)
- philipkglass 7y ago
  Yes. Hydrogenate CO2 to methanol with electrolytic hydrogen produced from clean electricity [1]. Reform methanol to hydrocarbons [2] that can burn in existing engines. (Or burn methanol itself in slightly modified engines. This offers somewhat lower energy density per tankful of fuel, higher total efficiency from electricity-to-motion.) Synthetic fuel makes sense for fueling aircraft, rockets, long distance shipping, collectible historic cars, and other niches. It doesn't make sense for fueling everyday ground transportation. Too much of the original energy is lost in the chain of chemical transformations and the chemical processing requires facilities on the scale of conventional oil refineries. The total cost is lower to electrify ground transportation and supply it with clean electricity than to transform clean electricity into liquid fuels for equivalent legacy vehicles. [1] https://www.frontiersin.org/articles/10.3389/fchem.2018.00446/full https://www.frontiersin.org/articles/10.3389/fchem.2018.0044... [2] https://en.wikipedia.org/wiki/Gas_to_liquids https://en.wikipedia.org/wiki/Gas_to_liquids
  - JumpCrisscross 7y ago
    > Synthetic fuel makes sense for fueling aircraft, rockets, long distance shipping, collectible historic cars, and other niches What's driving the emphasis on lightweight batteries for aviation over better synthesisation?
    - philipkglass 7y ago
      For UAVs, battery/electric systems don't just reduce fueling costs. They deliver features unobtainable from hydrocarbon engines: - Extremely long flight endurance without refueling (in large solar/battery UAVs) - Low noise - Odorless - Simpler and cheaper manufacturing The advantages are much less obvious to me for aircraft that transport passengers or significant cargo loads. I suppose that the companies developing them are hoping to make the lifetime total cost of operation cheaper than existing aircraft serving the same niche. That seems much tougher to achieve. EDIT: Bye Aerospace, the company described in the IEEE article, says they are targeting a particular niche: https://byeaerospace.com/eflyer/ https://byeaerospace.com/eflyer/ They intend to replace trainer aircraft that burn leaded aviation gasoline. This polluting niche fuel costs significantly more than kerosene. Maybe the economics can work out for this case.
      - JumpCrisscross 7y ago
        Thank you. Incredibly clarifying.
    - ajuc 7y ago
      There's no emphasis on lightweight batteries for passanger aircrafts, both batteries and biofuels are pursued and both are marginal compared to traditional fossil fuels.

throwawayhhakdl 7y ago

Biofuels always sounded wasteful to me. But this post makes a lot of good points on its merits that I hadn’t considered. How efficient is producing biofuels using renewable energy as a way of storing power long term?

nradov 7y ago

Alternatively, we can use electricity and heat from renewable power sources to synthesize kerosene from CO2 and water.

organsnyder 7y ago

For me, the experience of operating an electric vehicle is so much better than biofuels: refueling at home, simplicity of the drivetrain, and quietness/smoothness all are huge improvements over ICE vehicles. For your comparison between ICE and electric vehicles, are you counting the fuel processing and delivery infrastructure? Electric delivery infrastructure has very low emissions once it's in place, and production continues to get better (especially with distributed models like rooftop solar). Also, do you have a citation for "...lower energy requirements for building ICE cars versus batteries"? Yes, battery production is fairly intensive (economically and resource use), but (like I said above) the drivetrain is vastly simpler. I can't see how electric general aviation will become widespread without a monumental breakthrough. But it's hard to beat electric for ground-based transportation, IMHO.

svara 7y ago
This article addresses your questions: https://www.carbonbrief.org/factcheck-how-electric-vehicles-help-to-tackle-climate-change https://www.carbonbrief.org/factcheck-how-electric-vehicles-... Check out the "lifecycle greenhouse gas emissions" figures. It's really interesting in how it shows how different the total emissions are depending on which country you charge your electric car in. Also, depending on which electric car model you have, the lifecycle emission improvement over a conventional one might be relatively slim, depending on where and how much you drive it. By and large, electrics are at a substantial disadvantage due to both battery production and fuel cycle emissions, which then gets compensated over time as you drive the car. Edit: There's also this super interesting article on Wikipedia: https://en.wikipedia.org/wiki/Environmental_aspects_of_the_electric_car https://en.wikipedia.org/wiki/Environmental_aspects_of_the_e... which is largely consistent with the Carbonbrief article.
- Tade0 7y ago
  I've seen the graph there and I find one thing troubling: Lifecycle greenhouse gas emissions for conventional and electric vehicles (by country) in grammes CO2-equivalent per kilometre, assuming 150,000 kilometres driven over the vehicle lifetime. That's less than 100,000 miles - rarely do cars travel less than that during their lifetime. Specifically in my country that would mean using the car for ~10 years, meanwhile the average passenger vehicle age is 14 years! As for biofuels: land and water usage are major hindrances. For example you need ~1800 liters of water to grow 1kg of soybean. Sure, you can use waste products for fuels, but they need to be waste from something.

maelito 7y ago

> Due to the lower energy requirements for building ICE cars versus batteries, a biofuel powered car will be much better for CO2 emissions than an electric one What's the GHG emissions for the different types of biofuels ? What's the land use needed ? How abundant ? Etc.

biggieshellz 7y ago

For general aviation (small prop planes), it's because so much of the cost of running one comes from the engine. The most common piston engines are supposed to make it 1500-2000 hours between overhauls, and an overhaul runs around $16K, so you have to save $10-15 per flight hour in engine reserve to pay for the overhaul when it comes due and to cover any unexpected maintenance between overhauls. Plus, there are consumables that aren't cheap -- oil changes, spark plugs, and so forth. A brushless electric motor has a lot fewer moving parts, and a lot less vibration, so overhauls could be cheaper and with a larger interval between them, and regular maintenance would be cheaper as well. Plus, no leaded avgas to mess with, no worries about reduced power at higher altitudes where the air is thinner, no worries about carburetor icing or adjusting the air/fuel mixture. Sounds like a win to me.

TrueDuality 7y ago
Unfortunately the reduced power is still a problem at higher altitudes but for different reasons. Instead of oxygen starvation, the props will have less to push against. This is still less of an issue as the electric motor can spin faster due to the reduced resistance. Higher speeds will create higher resistances from within the motor itself (which will in turn be increase the heat generated in the motor). That heat will also be harder to dissipate in lower pressures, but I suppose alternative cooling could be added as well.
- dogma1138 7y ago
  I’m not entirely sure how you’ll cool the engines at high altitudes, combustion engines can use their exhaust to cool the engine. Using large radiators on an electric engine kinda defeats the purpose especially when they can’t be effectively be built into the body of the engine.
  - jandrese 7y ago
    I'm not sure why largeish passive radiators are a problem. If you're worried about the aesthetics you can put them inside of ducts and pass the air over them. This doesn't seem like it should be that big of an issue. Plus you'll probably want to recover some of that waste heat to heat the cabin.

the8472 7y ago

Combustion engines are quite inefficient and so are fuel synthesis processes. batteries have a high energy round-trip efficiency. The energy density does not matter as much in cars, which after mobile compute have been the primary drivers for technology. The density may make more sense for planes. Additionally 1st gen biofuels have poisoned the well to some extent due to competing with food crops.

throwawaycanada 7y ago

The only reason we have electric cars being pushed as much as they are is because of Tesla, specifically Elon Musk. It is not some government program. If it weren't for them we would have the Nissan Leaf and that is about it. And it wouldn't have half the performance that even it has today. Short answer: Monied interests don't really care, or don't think it is possible or feasible.

elihu 7y ago

Electric motors and batteries are very efficient, and therefore extremely cheap to operate. Biofuels make sense I think for aviation because you need that energy density to get a usable range, but the fuel is likely to be expensive for a long time. If you can figure out how to make liquid fuel for about fifty cents a gallon or so, it might be competitive with electricity for car use. I don't know what the energy requirements are for modern batteries, but I expect it varies a lot depending on battery chemistry. Battery sizes vary a lot, too.

nbanks 7y ago

For very short distance flights, electric aircraft are already viable. For example, Harbour Air Seaplanes operates a 20 minutes flight between Vancouver, BC and Victoria, BC. They use float planes because both cities are on the coast. Their first electric aircraft should take off in a couple months. One nice thing about electricity is that it's much cheaper than biofuels. This is because motors are much more efficient than engines, and because large generating stations are more efficient than small aircraft engines. BC is 95% hydroelectric which makes electricity even cheaper.

tim333 7y ago

>So why are we not heavily investing in biofuel infrastructure? I think the problems are more economics than physics. There was a huge investment in algal biofuels but it never proved economic. (eg https://www.greentechmedia.com/articles/read/lessons-from-the-great-algae-biofuel-bubble https://www.greentechmedia.com/articles/read/lessons-from-th...) I was a fan of Algenol for a while who were supposed to have algae that gave off ethanol cheaper than normal fossil fuel but it never worked out. Maybe something like that in the future will work.