Using Wind Turbines on Your Electric Vehicle
I’ve been asked many times over the years “why I don’t install a wind turbine on the front of my electric car to make it drive further.”
I’ve also had well-meaning advice on how I should install a generator attached to one of my car’s wheels, so that while driving along I can top up my batteries without plugging in.
To the novice it sounds perfectly logical, and a great way to boost your car’s range. But once you start to understand the energy losses involved, it starts losing it’s appeal. Put simply, because of inefficiencies, putting a wind turbine on your car’s roof will not boost your range. On the contrary; due to the wind resistance & extra weight of the fan, it’ll actually reduce your car’s total range.
If you’re like me, you’re probably not totally convinced yet, so to translate it into English I’ll run through some very basic calculations:
Let’s say your car needs 10 kW of power to drive along a nice, flat road at the legal road speed. In EV terms, that economy’s not too bad.
Now let’s say you put a wind turbine on the roof. This wind turbine puts out 0.5 kilowatts of power, which is wired straight to your battery pack. It sounds good so far, but this is where we have to factor in the inefficiencies (or losses) of the wind turbine.
Even if this wind turbine was a good one, at best it would be somewhere around 50% efficient. That means to put out that 0.5 kilowatts of power I mentioned, it’s actually using a full 1 kilowatt just to turn the generator behind the fan blades. That takes us back to zero (no gain at all).
Next on the list of losses is wind resistance (also known as drag) which pushes against the entire fan – and it’s more than you might think. Possibly another kilowatt of wind resistance. Remember when you were a kid and you had a little pinwheel fan on a stick? When you ran around, the pinwheel spun, but do you remember the pressure it put onto your hand? The stick pushes into your hand because there’s a good chunk of wind resistance in that little pinwheel. The same goes for a big turbine!
This all means that the wind turbine on the roof of our car is now causing the car’s motor to work harder to keep the car at the same speed, using (for argument’s sake) an extra kilowatt of power. There’s other losses to keep in mind too, such as weight, heat and noise losses and they all add into the total amount of energy used.
To sum it all up, let’s put it into a rough equation:
- Car Driving without fan: +10 kW
- Fan Generation: +0.5 kW
- Generator Resistance: -0.5 kW
- Wind Resistance: -1 kW
- Other Losses: -0.5 kW
So after installing the fan, you’ve come out worse off with an extra 1.5 kilowatts of power required to move your car along the same road, at the same speed with the fan on the roof. Altogether, the fan uses more power than it can create.
There is a positive side to this story though. The wind turbine can still serve a purpose on an electric vehicle, but only if the electric vehicle was not using energy at the time. For example, if the electric vehicle was parked, or if it was just rolling downhill you could use a turbine to top up the battery pack. In that case there is available energy being wasted which could be reclaimed.
That’s the effect of wind turbines on electric vehicles in a nut shell. As for bedeni motors & perpetual motion machines, they’re a whole other story.