I'm no scientist, and I'm even less of an expert on climate change, so please forgive me if this is a stupid question, but if a diesel generator is used to charge the battery in a car, isn't it more efficient to just drive a diesel-powered car? I'm not trying to be funny or sarcastic. I'm honestly asking because I want to know if it makes sense to use a diesel generator for this purpose.
To my understanding, there are several factors at play here that pretty much ends in an answer of "it depends" .
If we assume the transmissions have equal losses (this is generally not a good assumption because electric and hybrid cars typically use more efficient transmissions, like the single-speed ones in Teslas and the HSD in Toyotas).
On the diesel-driven car side, the salient measure is the efficiency of the diesel engine at converting the chemical energy in the fuel to movement.
One the electrical car side, there are more possible steps where losses can accrue:
1. Efficency of the generation process : how much of the total energy in the diesel is used to generate the required electricity
2. Efficency of charge/discharge: how much energy is lost in the charging and discharging of the battery
3. Efficency of the motor at converting electricity to movement
Now this sounds like a lot more potential for energy loss, but the net isn't quite so clear because diesel engines are still generally less efficient than the equivalent generators due to the need for the car engine to rev up and down (compared to steady-state for the generator), which means they operate outside of their maximum efficiency range. The ability for a generator to run at steady-state is why there has been some exploration of using turbine and rotary engines in this application.
I think a good example of "it depends" is how the Chevy Volt drivetrain is designed. It is (sort of) designed as a series hybrid, where the engine primarily serves as a generator for the battery, which in turn drives the wheels with an electric motor. However, there are situations where a clutch engages in the transmission, mechanically coupling the engine to the rest of the drivetrain because it is the most efficient drive option. I'm not familiar enough with the Volt to tell you what those situations are.
I think a big argument for electric cars (and I really
hate the smugness with which many of my fellow Tesla owners do it) is that centralized generation of electrical power is generally going to be more efficient than distributed generation (which is effectively what we're doing with car engines), even taking into account transmission and battery losses. In addition, upgrades to large-scale generation are broadly more economically feasible when fitted at scale than a distributed solution. For example, it's financially easier to justify a retrofit of a super-high-efficiency particle filter on a coal plant than to retrofit similar filters on millions of diesel cars. As a result, upgrades to power generation facilities automatically trickle down to the electric cars that use that power.
I know it's kind of a lot of text, kind of complicated, and my knowledge is kind of surface-level, but I hope it helps.
you can find a more in-depth analysis of energy efficiency in this research report from Argonne National Laboratories though it is focused on plug-in hybrid electric vehicles (like the Volt):