That’s a BMW i3 by the looks of it. It has a 120 Ah batteri (BMW speak) or 42 kWh in the usual jargon. Charge it with 42 kW, and in one hour it is fully charged. However, it can be charged with 50 kW max, and it takes 40 minutes to charge it to 80%. I would think about an hour to 100%, but it will typically charge at a lot less then 50 kW for the last 20%
This means using only 50/350 = 14% of that 350 kW generator, and it charged in less than an hour from empty.
Or, with 350 kW, you can charge 7 BMW i3 (120 Ah) within one hour, and they will run for approximately 300 km.
That’s a total of 7*300 = 2100 km , or 1305 miles using 12 gallons. A total of 109 miles per gallon 
109mpg is not realistic, otherwise you could build a car which has a diesel generator driving electric motors and it would do 109mpg, which we know nobody has achieved because if it worked everybody would be making them.
The truth is probably somewhere in between. Most likely around 20-30mpg area.
Neither is 5.6 mpg However, 109 mpg is at least based on data. mpg tells me nothing anyway.
109 mpg is 0.22 liters per 10 km (or liters per mile as we say around here). Certainly plausible for an optimized diesel/hybrid vehicle driving carefully. I even think such vehicles are commercially available.
5.6 mpg is 4.2 liters per 10 km, which is the typical 40 ton truck on the roads. To get 5.6 mpg requires an efficiency of approximately 5% of the 350 kW diesel engine. This isn’t physically possible without the engine melting down within a few seconds, because 95 % of the power is used purely for heating the engine.
109 mpg is much closer to the truth than 5.6. If I would guess, I’d say it would use around 0.3-0.4 liters per 10 km. It’s not clear to me how that charger actually work though. I would think it’s a simple diesel engine running a synchronous AC generator, that directly charges the car using 11-22 kW AC, rather than some fancy, but less efficient AC/DC conversion etc. If it is, then I see no reason why the 109 mpg is a “insane” number, it’s probably slightly optimistic? 0.3 liters per 10 km is not, and 0.4 liters per 10 km is on the bad side.
You can get 109mpg from a petrol or diesel vehicle, but not one which is practical / which is driven in a useful way.
There’s an assumption here that the generator is reasonably efficient. My take on it is that the engine/generator setup is burning a lot of fuel even when it is producing no useful output, a bit like when you do a ground run-up. My O540 produces about 170 hp burning 14 gals/hour. A modern diesel should do a bit better. But maybe a lot of energy is being wasted somehow in the setup?
What “kills” the efficiency in a normal car, is the engine seldom runs at best efficiency. It stops, accelerates, go uphill, downhill. A hybrid can mitigate this to some degree, a rather large degree actually, but it depends on the driving pattern. Not much on a flat highway at constant speed, but a lot when driving in the city.
An electric vehicle converts 80% of the power from the “plug” (or grid) to the wheels. A gasoline/diesel vehicle converts 15-30 % depending on the driving pattern. A diesel engine used for power generation has 40-45% efficiency. A synchronous generator has way above 95% efficiency, but lets say 95% for a small one.
The efficiency of a diesel power generator + EV is in the order of: 0.8*(0.40 to 0.45)*0.95 = 0.3-0.35 (30-35%), lets say 32.5 %
The efficiency of a gasoline/diesel car is still only 15-30% and highly dependent on driving pattern. Let’s make it 22.5% on average.
The truth is that even with that “outrageous” diesel generator, an electric vehicle will be more efficient by a factor of 1.44 compared with a gasoline/diesel engine car.
Great calculation! Actually on the conservative side since high output diesel engines used at max efficient RPM approach (and two-stroke diesels exceed) 50% efficiency, although we don’t know what they are using in these generators.
A larger diesel power generator can also have secondary cycles for hot water supply and so on, making the efficiency very high. This still shows a few things.
If the energy comes from internal combustion, then the benefit of EV is mostly due to the ability to run the power generation at best efficiency. If this can be done in the vehicle itself, than not much is gained with an EV. For instance the largest ships having diesel engines with an efficiency of 50%+
Long distance travel in the air won’t necessarily benefit all that much from going electric, even though the problem with energy density in batteries are solved. Short distance travel on the other hand, replacing small TP aircraft with electric ones for short hops of less than 1/2 to 1 hour will have a huge potential, even if the energy is created by dedicated diesel power generators on the ground. The energy efficiency of a diesel generator is as high as it gets, while the total energy efficiency of a TP doing short hops at low alt is as low as it gets.
Peter wrote:
You can get 109mpg from a petrol or diesel vehicle, but not one which is practical / which is driven in a useful way.
I think not one that is practical for all purposes. Sometimes people need to move large furniture or lots of children, so we buy cars that are big enough to meet these needs. But I’m just off now to buy some milk, by myself, and there are vehicles capable of much more than 109mpg that are perfectly suitable for this.
LeSving wrote:
even though the problem with energy density in batteries are solved.
How?
kwlf wrote:
I think not one that is practical for all purposes. Sometimes people need to move large furniture or lots of children, so we buy cars that are big enough to meet these needs.
I think we did this discussion before with some of the same participants and perhaps also @Silvaire. It comes down to people not being satisfied with a vehicle that fulfills their mission ~80% of the time and preferring something closer to 99%.
