Muhammad Talha It is evident that Darrieus turbines have efficiency comparable to Horizontal axis wind turbines, but they need a large amount of space and are complex to maintain and operate. The Savonius turbine has a lower power output and efficiency, yet it can function at lower wind speeds effectively. Wind from numerous directions is likewise acceptable for a Savonius turbine because as it can harvest wind from any direction. Also, an additional power source is a demand of Darrieus turbine to start the turbine rotation, which leads to cyclic stress on the turbine tower. Apparently, Savonius wind turbines are irrespective of any external power source for the starting process, and they are frequently used in the areas where turbulent wind occurs.

When we look at the all above aspects, I believe that a Savonius turbine could perform effectively in your context.

Winds on a moving vehicle are generated by the movement of the vehicle and in a sense resulting from the energy of the engine. If you extract the same energy by a wind mill, your engine may have to work harder. Some people may argue that this is like recovering waste energy, however, before deploying a windmill concept, one must prove that such windmill on vehicle will not cause an extra burden on the engine.

Darrieus turbines are efficient. find the link attached herewith

Article Comparative study of a three-bucket Savonius rotor with a co...

It depends on the field operation conditions, Darrieus turbine needs a high starting torque and not very practical under low velocity conditions in its original design ( however now there are many modificaciones helps to start easily). Savonius selection is a rapid solution for commercial purposes but with a very bad efficiency… it is a periority selection.