Much hype and experimentation has existed around the concept of e-fuels. Briefly, the plan is to extract CO2, ideally from air, sprinkle in some green hydrogen and make whatever fossil fuel product is desired. That all sounds great, but runs into several practical problems, mostly around compound losses both when we turn renewables into fuels (50% losses), and when its burned in say a car (80 – 90% losses). Hence in an automotive applications, only 5-10% of the input electricity actually moves the wheels.
Lets begin with the process of converting electricity into fuel. Briefly, its possible to manufacture simple “hydro-carbons” such as methane via a process called steam reforming (source). The resulting methane then needs to be joined together to form the longer hydrocarbon chains found in say motor gasoline. To do this, one needs to supply hydrogen, and ideally carbon monoxide (although carbon dioxide can be used too, albeit with processing to produce CO from CO2). There are several mechanisms to achieve this, but the Fischer-Trophsch process is often mentioned (source).
Efficiency figures of about 50% are often quoted, while some have suggested close to 80% efficiency is possible, presumably these do not include the effort involved in producing hydrogen, and obtaining CO or CO2. While direct air capture would be ideal, the relatively low levels of CO2 in the atmosphere (~ 0.4 %, source), means that extracting CO or CO2 from the atmosphere is going to be energy intensive.
To keep things simple, lets go with 50%, so what that means, is that half of the electricity that goes into hypothetical e-fuels process actually winds up in the finished product. To put some numbers to that, 1 liter of motor gasoline contains 9.3 kWh (source). Hence Id need 18.6 kWh of electricity to produce 1 liter of motor gasoline. Thus to “fill” the tank of a say Nissan Versa, with a 40 l fuel tank, Id need whopping 744 kWh of electricity. But the fun does not stop there, as only about 10-20% of the energy in gasoline winds up moving the wheels (source). Combining these two, we arrive at only about 5-10% of the input electricity finding its way to the wheels. Compared to charging my Nissan Leaf (~95% efficiency), and the inherent efficiency of EVs (~76% source) combine to make 72% of the electricity going into my Leaf actually moving the wheels. That’s a lot better than 5-10% from E-fuels.
Hence, for automotive applications, the efficiency story is clear, EVs are an order of magnitude more efficient, which is why my roof can power my EV, but would struggle to produce meaningful amounts of E-fuels.
These days, about half of a barrel of oil winds up as motor gasoline (source). Hence, naturally, big oil, whose business is extracting and refining oil might be conceivably concerned if all of us start driving EVs. This has caused some to suggest that E-fuel efforts are just another fossil fuel misinformation campaign.
Recently a company announced an interesting concept, a refrigerator sized contraption that apparently does the above and produces fuel from electricity and the air (source). As discussed above, I am skeptical of these claims, as the amounts of electricity needed to produce meaningful amounts of fuel are quite high.
Personally, I feel E-fuels have a role in the future, while I am skeptical of automotive applications, as EVs are SO much more efficient, two applications make a lot of sense for me: Aviation and backup winter-home heating.
To begin with Aviation, currently batteries are heavy, and heavy things don’t like to fly. Jet engines are actually quite a bit more efficient than gasoline engines for cars (something to do with not needing to “step-on-it” to pass someone on the highway), hence electricity to “thrust” would be something like 10-20% efficiency, thats a lot better and might actually work, given that the overall system (fuel + engine, vs batteries and motors) is a lot lighter, which translates into better efficiency (source).
Backup home heating is another contender. Last winter (and it was a cold one), I needed about 100 m3 of natural gas for backup heating. That’s a lot better than the 2500 m3 of natural gas used by the average Canadian household during the year (source), thanks to my heat-pump that does most of the work. But, I do need to get through those few very cold winter days, where the temperature drop below what my heat-pump can do.
Enter e-fuels, my 100 m3 would require 2273 kWh, which is about a months work of sunny days for my rooftop solar setup. Seems plausible such surplus energy could be found, and probably stored too from the sunny summer months to those cold winter days.
I feel that E-fuels have a future, aviation and backup home heating are much more promising applications than terribly inefficient gasoline cars.
Electric car adventures 