[Yo-Yo]

Last I checked, these small wind turbines use automotive alternators to generate power, and automotive alternators have built-in magnetic field regulation so that no matter how fast you spin them, they don't overcharge the battery.

Some secret sauce...

[waterhill]

Have a friend in NC that generates/recharges a battery bank with a river/alternator system.

[delta7]

A Doubting Thomas here. Drag. The drag produced by the platform is drag, plus the drag of the blades, plus the most important fact- the energy required by the moving vehicle to rotate the generator is largest factor.

Even our modern day alternators rob the engine of horsepower ( energy), I would be surprised if all the drag and strain on the engine ( more gasoline required) would barely exceed the “ windmill” energy output.

https://thepowerfacts.com/how-much-power-is-needed-to-turn-an-alternator/