8 ms·

Sure, but if you separate the carbon from the oxygen and return the oxygen to the atmosphere you reverse the process and you’re back to, simply, having to deal

by avalys 5y ago

Sure, but if you separate the carbon from the oxygen and return the oxygen to the atmosphere you reverse the process and you’re back to, simply, having to deal with roughly the same mass of fuel as you originally burned. Which is obviously a tractable problem since you burned it in the first place. If we had a good way to make synthetic gasoline from energy + carbon, we could have a totally carbon neutral fuel cycle where we use nuclear power to extract carbon from the air and produce synthetic gasoline.

adrianN 5y ago
Depending on your definition of "good" we already have ways to make liquid fuel from CO2+energy [1]. It just that you lose something like 90% of the energy from power plant to motion. Electric cars are much more efficient. [1] https://en.wikipedia.org/wiki/Synthetic_fuel https://en.wikipedia.org/wiki/Synthetic_fuel
kwhitefoot 5y ago
It's monstrously inefficient to use nuclear power to create hydrocarbon fuels, truck them to petrol stations, and then burn them. "Modern gasoline engines have a maximum thermal efficiency of more than 50%,[1] but road legal cars are only about 20% to 35% when used to power a car. In other words, even when the engine is operating at its point of maximum thermal efficiency, of the total heat energy released by the gasoline consumed, about 65-80% of total power is emitted as heat without being turned into useful work, i.e. turning the crankshaft" See https://en.wikipedia.org/wiki/Engine_efficiency#Gasoline_(petrol)_engines https://en.wikipedia.org/wiki/Engine_efficiency#Gasoline_(pe... And the heat engine efficiency limits are only one part of the problem. Extracting the CO2 from the atmosphere also costs a lot of energy. It is more efficient and simpler to just use the existing electricity grid to charge electric vehicles. "For an electric vehicle, energy efficiency is estimated at 90%, " See https://www.renaultgroup.com/en/news-on-air/news/the-energy-efficiency-of-an-electric-car-motor/ https://www.renaultgroup.com/en/news-on-air/news/the-energy-...
- beerandt 5y ago
  >For an electric vehicle, energy efficiency is estimated at 90% Just because you draw the system boundaries with the inefficiencies outside, doesn't make them disappear. Power generation, transmission, and distribution is on the order of 30%, before you take into account the inefficiencies of battery charging.
  - nix23 5y ago
    >inefficiencies of battery charging And the huge amount of energy for producing/recycle them.
  - adrianN 5y ago
    You have power generation, transmission and distribution also when you want to generate synfuel.
    - funcDropShadow 5y ago
      But the details may differ. If you can generate the synthetic fuel near the energy source, let's say a wind, farm you can shift the cost of transportation from one medium to another. That opens up possibilities to optimize on a network scale. In Germany, there is a pipeline network to transport and store natural gas to many many places. That transport is happening without trucks or ships driving around, I assume there are some pumps involved. But you don't have to move overhead mass.
- mrjin 5y ago
  Charging the battery itself alone might be efficient. Take your 90% efficiency as true, and assume electric motor efficiency as 90% too, now the net efficiency drops to 81%. To reach your home, there most likely at least one step-up transformer and 2 or more step-down transformers. Assuming all those transformers are super efficient with a efficiency of 90% too, then the efficiency now becomes 65.61% for two transformers scenarios, 59.049% for 3 transforms scenarios. Considering the cost of manufacturing the battery, the huge weigh of the battery(85kWh now weighs around 540kg), the overhead of the power grid as a result of staggeringly over provisioning needed: assuming charging a 85kWh battery from 0% to 100% in 1 hour, using 220V AC power, nominal current required is 85 * 1000(kW) / 220(V) = 386.36A. Assuming power factor 80%, then the required currency is 386.36/0.8=482.95A, how much is going to cost for that capacity? 1 hour might be too aggressive, let take a concession to 8 hours, then the currency required is 60.37A. Just take look at your home's fuse, how much is that rating? Let's take another concession to require only 50% charge, then the required currency is ~30.19A, which is still around 10 times normal off-peak usage or ~3 times peak hour usage. Are you seriously considering to increase the capacity of the whole power grid by 3 to 10 times just for charging the car at home to 50% juice in 8 hours?

by avalys 5y ago

adrianN 5y ago

Depending on your definition of "good" we already have ways to make liquid fuel from CO2+energy [1]. It just that you lose something like 90% of the energy from power plant to motion. Electric cars are much more efficient. [1] https://en.wikipedia.org/wiki/Synthetic_fuel https://en.wikipedia.org/wiki/Synthetic_fuel

kwhitefoot 5y ago

It's monstrously inefficient to use nuclear power to create hydrocarbon fuels, truck them to petrol stations, and then burn them. "Modern gasoline engines have a maximum thermal efficiency of more than 50%,[1] but road legal cars are only about 20% to 35% when used to power a car. In other words, even when the engine is operating at its point of maximum thermal efficiency, of the total heat energy released by the gasoline consumed, about 65-80% of total power is emitted as heat without being turned into useful work, i.e. turning the crankshaft" See https://en.wikipedia.org/wiki/Engine_efficiency#Gasoline_(petrol)_engines https://en.wikipedia.org/wiki/Engine_efficiency#Gasoline_(pe... And the heat engine efficiency limits are only one part of the problem. Extracting the CO2 from the atmosphere also costs a lot of energy. It is more efficient and simpler to just use the existing electricity grid to charge electric vehicles. "For an electric vehicle, energy efficiency is estimated at 90%, " See https://www.renaultgroup.com/en/news-on-air/news/the-energy-efficiency-of-an-electric-car-motor/ https://www.renaultgroup.com/en/news-on-air/news/the-energy-...

beerandt 5y ago
>For an electric vehicle, energy efficiency is estimated at 90% Just because you draw the system boundaries with the inefficiencies outside, doesn't make them disappear. Power generation, transmission, and distribution is on the order of 30%, before you take into account the inefficiencies of battery charging.
- nix23 5y ago
  >inefficiencies of battery charging And the huge amount of energy for producing/recycle them.
- adrianN 5y ago
  You have power generation, transmission and distribution also when you want to generate synfuel.
  - funcDropShadow 5y ago
    But the details may differ. If you can generate the synthetic fuel near the energy source, let's say a wind, farm you can shift the cost of transportation from one medium to another. That opens up possibilities to optimize on a network scale. In Germany, there is a pipeline network to transport and store natural gas to many many places. That transport is happening without trucks or ships driving around, I assume there are some pumps involved. But you don't have to move overhead mass.
mrjin 5y ago
Charging the battery itself alone might be efficient. Take your 90% efficiency as true, and assume electric motor efficiency as 90% too, now the net efficiency drops to 81%. To reach your home, there most likely at least one step-up transformer and 2 or more step-down transformers. Assuming all those transformers are super efficient with a efficiency of 90% too, then the efficiency now becomes 65.61% for two transformers scenarios, 59.049% for 3 transforms scenarios. Considering the cost of manufacturing the battery, the huge weigh of the battery(85kWh now weighs around 540kg), the overhead of the power grid as a result of staggeringly over provisioning needed: assuming charging a 85kWh battery from 0% to 100% in 1 hour, using 220V AC power, nominal current required is 85 * 1000(kW) / 220(V) = 386.36A. Assuming power factor 80%, then the required currency is 386.36/0.8=482.95A, how much is going to cost for that capacity? 1 hour might be too aggressive, let take a concession to 8 hours, then the currency required is 60.37A. Just take look at your home's fuse, how much is that rating? Let's take another concession to require only 50% charge, then the required currency is ~30.19A, which is still around 10 times normal off-peak usage or ~3 times peak hour usage. Are you seriously considering to increase the capacity of the whole power grid by 3 to 10 times just for charging the car at home to 50% juice in 8 hours?