Re: Wind Turbines and Automobiles

The question: Could wind turbines provide significant extra energy for an 
automobile if it was travelling at high speeds?




Hello Dawod,
Unfortunately, the answer is ‘no’- any gain in (electrical) energy from a 
turbine would be more than offset by the additional resistance that the 
turbine would place on the automobile engine.  
A wind turbine is a device that captures the energy in a moving stream of 
air by changing the kinetic energy into electricity.  However, in physics 
and thermodynamics, nothing is free!  The amount of electrical energy 
that is produced will be less than the amount of energy that is extracted 
from the moving airstream.  This is because of inefficiencies in the 
energy conversion process.  There are friction losses and electrical 
losses in the generator itself.
So how does this energy loss translate to what would happen to a turbine 
mounted to a car?  Let’s say that the car is travelling at 60 mph with 
the turbine facing into the oncoming airstream.  The spinning turbine 
would indeed be extracting energy from the air.  However, there would be 
a resulting force on the turbine acting in the opposite direction of the 
car’s motion.  This force would move through the turbine mount, and act 
directly on the car, putting a load on the car’s engine.  The extra power 
that the engine must exert is equal to the resisting force times the 
speed of the car.  (In physics, power is equal to force x velocity).  I 
said above that a turbine extracts energy from the wind, but in this 
case, our “wind” is created by pushing the turbine through the air, and 
the energy extracted must come from the propelling force- the car 
engine.  
Here is an interesting fact to consider relating to wind turbines:  Have 
you ever seen fields of giant wind turbines?  These turbines, fixed to 
the ground are getting their energy from the wind and turning it into 
energy to be added to the electric grid.  But, even though the turbines 
are fixed to the ground, this energy is not free.  This energy 
is “extracted” from the moving air, which means that the wind leaving a 
turbine field actually slows down.  There is actually a limit to the 
number of turbines that can be installed in a field because the wind 
downstream of other turbines becomes too slow to effectively power the 
turbines in the back!
I hope that this is helpful
Best Regards,
Jay Shapiro