This paper is interesting in that it goes into the details of modding a 250cc motorbike engine to suite the chosen generator so that you end up with a light, compact and efficient genset for your city commuter (mostly) EV, without using electronics to get the required Volts and Amps for your battery.
I like the simplicity of Serial Hybrids vs the complex drivetrain and control reqd for parallel hybrids.
Tuning and tweaking an ICE to run efficiently at a constant rpm is also much simpler than trying to get the ICE efficient over a wide rev range.
ie: The optimal cam profile, ignition timing and intake and exhaust lengths are all constant and achievable without electronic ignition and VVT etc-etc.
As grid power here in the 'New South Africa' is more off than on; Serial Hybrids also give one the option of always having house power when you get home in said vehicle..!
https://sci-hub.se/10.4271/2011-24-0085
Another link for any (2wd) bikers here, where something similar was done:
https://endless-sphere.com/sphere/th...d-hubs.110812/