Yes the propeller is powered by the wheels. Yes it is silly. Many things in physics are silly yet correct.
Yes air applies a force on the car, which pushes it. Amazing, no?
By the way, you didn't tell what was the engine providing 3MW to a wind turbine so that it can stay at the same place.
Wheels are not a power source (they are not radioactive and not being burned to extract energy from them). Wheels are an intermediary but power to any part of the (wind powered vehicle) can only be provided by air particles hitting the vehicle body (any part of the body including the propeller blades).
When air particles hit the direct downwind vehicle from the back (wind speed higher than vehicle speed) the wind power is available to vehicle to accelerate in the desired direction and or store that.
When vehicle speed equal wind speed there is zero available wind power to vehicle and when vehicle exceeds wind speed the vehicle will now hit the air particles so wind power available to vehicle will be negative meaning will slow down the vehicle unless as it is the case here vehicle also has access to earlier stored pressure differential that will be used to cover vehicle friction losses including air drag.
The stored high pressure and low pressure created by the propeller is called pressure differential energy storage.
That pressure differential was created by the propeller using wind energy while vehicle speed was well below speed then after that this stored energy is what powers the vehicle for the next few minutes (how many minutes or seconds depending on how high you set the acceleration rate).
The 3MW wind turbine is anchored to the ground so what is being accelerated is the entire earth and obviously a 3MW wind turbine will not make any measurable difference to such a large mass but it can be calculated as we know the mass and speed of air particles the equivalent area of the wind turbine and the mass of the earth.
You can imagine this 3MW wind turbine installed on a 4 wheel platform with say a weight of 1000kg including the wind turbine weight and then you can imagine this 4 wheel platform on a 200000kg 4 wheel platform that sits on the ground.
Wheels are ideal with no friction.
The 3MW for 1ms will provide at least 3000Ws (this is absolute minimum not to violate energy conservation) to the 1000kg 4 wheel platform
So starting from zero kinetic energy the platform will end up with 3000Ws
3000Ws = 0.5 * 1000kg * v
2So after this 1ms the platform speed relative to the large platform will be
sqrt(3000Ws/(0.5*1000kg)) =
2.45m/s relative to both the large platform and ground.
Now if the small wheel platform is anchored to the large 4 wheel platform (say brakes are enabled).
Then that same energy will be transferred to the large platform
Now the weight is 201000kg
3000Ws = 0.5 * 201000kg * v
2 so speed of the large platform after 1ms
sqrt(3000Ws/(0.5*201000kg)) =
0.17m/s relative to ground
Now if you apply the brakes to large platform also the energy will be transferred to planet earth and if you know the mass you can calculate the speed increase of the planet after 1ms.