I'm curious about series hybrids (Plug-In, or range extended EVs), and this has me wondering. I see that a 2016 Chevy Volt has a 53 KW generator and a 101 HP (75 KW) engine. It can run in full EV mode for ~ 50 miles, with reasonable acceleration and speed. Based on some approximations I've made it seems like something more like a 20 KW generator, and matching engine should be sufficient. Why such a large gap? I base this on battery capacity range of several EVs and some general numbers I've heard, that it only takes about 25 HP to maintain a car at highway speeds. When I take the EV range, and assume 60 mph at that range (a mile-a-minute) and the battery kWh, I come up with a ballpark of < 20 KW average for those vehicles. And estimate ~ 25-30 HP engine to account for 10% generator losses? In the ballpark, right? I'm further assuming that the 20 KW average would be more than enough for city driving, you get regen braking, and while stopped the engine is charging the batteries, so average power is far lower than the peak for the stop/go acceleration. Secondarily - I also know that the Chevy Volt runs the engine in parallel with the motors in some modes. This makes sense, as they avoid the losses in rotary>electrical>rotary conversion, and in the case where the energy is being stored in the battery (like when stopped), the round-trip losses of the battery charge-discharge. But the drive system seems so complex to me. Why not use an engine optimized for a narrow speed/power range (perhaps a high efficiency HCCI?), and couple it through a relatively low power handling CVT? Apply no more power/torque than the ~ 25 HP number from above? That would be far less demanding of a CVT than the kind in ICE cars, which must handle the full power/torque of acceleration. If the engine were only used to assist with ~ 25 HP from say 20 mph to 80 mph, over a narrow RPM range of the engine, a 5:1 ratio range, lightweight CVT could do the matching. CVT's in use today have ratio ranges wider than that. Power not required to propel the car would be directed to the battery (I'm assuming they can control the gen load/output through the field current?). Wouldn't that be simpler? What am I missing?