It's hard to make an engine that runs at peak efficiency at a range of speeds and power demands. But when batteries are added, the picture can change quite a lot.
The engine can be built and sized to run efficiently at a fixed speed, and its power output never needs to exceed whatever the generator that it drives is able to accept.
So when it runs, the combined engine+generator set can be run full-assed. No half-assing required. It's a binary state. On, or off. Full-staff, or flaccid.
By reducing variables in this way, all of the fuel that is burned gets converted to electrical power as efficiently it can be for the process at-hand. (It's also easier to quiet an engine that runs at a fixed speed than one that runs at variable speeds; things get a lot simpler when there's only one set of identified frequencies to bother with.)
While the engine is on, some of that electrical power can get used for driving an electric motor for propulsion and the rest can go into a battery.
If it is on and the vehicle is stationary, then all of that electrical power can go into a battery while the engine is remains at full-chooch.
When the battery gets full-enough and/or demand is low-enough, then the engine can just turn completely off. In this mode, all of the electrical power used for propulsion then comes from the battery.
It works. There's even some boats[1] that use these concepts.
It's just an unusual arrangement for now. (It may always be an unusual arrangement if the goal is to eliminate localized combustion of fuel. But as we keep being reminded over and over on these pages, whenever a headline about vehicular electrification comes by: We aren't quite uniformly there yet.)
It will be interesting to see how much more subsidy ICE cars require as they disappear over the next 10 years.
Around me (Ohio, USA), nearly every car I see is gas-fired. I only see an occasional EV; they tend to stick out, and they're very unusual.
Things look different when I travel to different areas of the US, though. Poorer areas have even fewer EVs than I see around here, while wealthier areas have a lot more of them.
It's a little bit unusual for me to encounter an EV at all during my ~daily driving (often about 40 miles, all said).
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For my part: My lifestyle requires a minivan that can serve as a work truck. There are zero EV options for that here.
But if I could get one with 250 or 300 miles of capacity, then I'd have a new goal. :)
Probably not all that rural by US standards, but it is by UK standards.
The EV rollout is still early stages here too. If we had regional electricity pricing (contentious question!), Scotland would have cheaper electricity and potentially at zero on many occasions.
(ID Buzz? Very expensive though)
I’m in the U.K. and couldn’t afford to not have an EV, could cost over £2500 a year more to drive a petrol car.