Efficient, carbon neutral fuel for cars

[Czcibor]

Assuming that a carbon neutral fuel for cars has to be used, what would be most practical and efficient? (Assumption: there is electricity from hydropower/nuclear or possibility to grow plants for biofuels)

1) Hydrogen from water hydrolysis?
(If I get it right, production is simple but the challenge starts with storage of liquid hydrogen)

2) Go next step and get methane from Sabatier reaction?
http://en.wikipedia.org/wiki/Sabatier_reaction

3) Go even a step further and get a liquid fuel through steam reforming?
http://en.wikipedia.org/wiki/Steam_reforming#SMR

4) Biomass gasification and get fuel a liquid fuel from it?

5) Or maybe just produce biofuels from crops / algae / whatever?

Which of those process would be worth using? With contemporary technology, but some serious adjustments in infrastructure are possible. I mean not only energy loses at production but also practicality of easy to transport and storage of fuel.

 

[Bystander]

carbon neutral fuel for cars

transport and storage of fuel.

You have identified the economic limiting factor, and that liquid fuels are the only way to go. You have likewise identified the problem that synthetic liquid fuels are net energy losers in terms of the energy lost in synthesis.

most practical and efficient?

Fischer-Tropsch liquid fuel synthesis from organic feedstocks in nuclear or solar thermal fired plants? That might actually be a way around the solar-thermal nighttime energy storage problem.

 

[russ_watters]

Why have batteries been excluded from this?

Also, imo, assuming we've already converted our entire electrical grid to non-carbon fuel is putting the cart before the horse.

 

[Czcibor]

You have identified the economic limiting factor, and that liquid fuels are the only way to go. You have likewise identified the problem that synthetic liquid fuels are net energy losers in terms of the energy lost in synthesis.

Fischer-Tropsch liquid fuel synthesis from organic feedstocks in nuclear or solar thermal fired plants? That might actually be a way around the solar-thermal nighttime energy storage problem.

Sounds reasonable.
Now I have one argument against converting natural gas to gasoline. Iran which is in situation where it may be a possible idea, actually prefers just compressed natural gas as fuel for cars and even created a dedicated engine.

Why have batteries been excluded from this?

Also, imo, assuming we've already converted our entire electrical grid to non-carbon fuel is putting the cart before the horse.

I forgot them. You want to say that batteries would be the choice or that just would be one of possibilities?

 

[russ_watters]

I forgot them. You want to say that batteries would be the choice or that just would be one of possibilities?

I think they are probably the best choice -- they are considerably more efficient than at least the first three you listed.

 

[Czcibor]

I think they are probably the best choice -- they are considerably more efficient than at least the first three you listed.

More efficient after including lifetime of the battery?

Anyway - for city cars - what about trolleybusses/trolleytrucks / trolley... passanger cars(?) (assuming that anyway infrastructure can be changed)?

 

[phyzguy]

Of course, nobody knows which of these options will ultimately prove to be the best, otherwise we wouldn't see people investing in all of these options today. Having said that, my opinion is that one of the following two will win out:

(1) Batteries will improve to the point that we don't need liquid fuels and will drive pure electric cars.
(2) Biofuels produced from algae. Today, the company Algenol is saying that they will be able to produce ethanol directly from algae for $1/gallon. Their technology uses seawater to grow the algae in desert climates, so it uses neither fresh water nor arable land.

We might also see both battery and liquid fuel options continue. I think it is much easier to get passenger cars to work on batteries than it is heavy equipment and airplanes, so liquid fuel might continue to be the fuel of choice for these even if batteries improve.

 

[Bystander]

(1) Batteries will improve to the point that we don't need liquid fuels and will drive pure electric cars.

This is counting battery mass as payload?

seawater to grow the algae in desert climates,

Material handling costs for moving seawater to deserts are going to be what?

 

[phyzguy]

Material handling costs for moving seawater to deserts are going to be what?

They don't pipe seawater inland, they build their facilities in desert regions along the coast, of which there are many (Mexico, Chile, Western Africa, Australia, ...).

 

[Bystander]

If the ponding is done at sea-level, what's the necessity of locating in desert regions?

 

[phyzguy]

If the ponding is done at sea-level, what's the necessity of locating in desert regions?

Land is cheap. Coastal areas with adequate rainfall tend to be heavily populated.

 

[dougfgd]

A fuel cartridge to be engineered that absorbs CO2 in series with or as a replacement f
or the CAT and is exchanged when fuel is taken on board.The old cartridge to be used as a building material.
Car connected up as CHP when not commuting.
2 state Thermal storage cartridge used to store 70% wasted combustion energy and used to heat/cool the home

 

[jack action]

Why have batteries been excluded from this?

Wouldn't batteries be more of an energy storage device than a fuel? Unless someone would consider disposable batteries!

 

[dougfgd]

All intermediate fuels and that includes electricity require further inefficient stages. I fail to see the advantage of electricity which must need not only a 50% generation energy loss followed by a 30% distribution loss followed by a 30% storage loss.
Better to concentrate on an efficient engine, an efficient drive train and not to waste the unwanted heat; store it and take it home for heating. And while you are doing that plug the car generator and cooling into the home as CHP.

 

[russ_watters]

More efficient after including lifetime of the battery?

I don't know what that means/how you would quantify that. If you mean cost effective, that's tough to say, since the infrastructure for the others doesn't exist. I'm not very optomistic about hydrogen, though, because neither fuel cells nor hydrogen internal combustion engines are very efficient.

Anyway - for city cars - what about trolleybusses/trolleytrucks / trolley... passanger cars(?) (assuming that anyway infrastructure can be changed)?

Already exist, but sure, there are ways to make them more efficient, such as making them hybrids.

 

[russ_watters]

Wouldn't batteries be more of an energy storage device than a fuel?

Yes - as far as I can tell, all of the first three proposals are storage methods instead of dug-out-of-the-ground fuels. The required assumption is made in the first line of the OP though: that we've already converted all of our electrical production to renewable/clean sources before having extra clean power to use for transportation.