Wind power is one of the primary renewable energy sources. Small wind turbine market is growing considerably and forecasted to reach to five GW by the year 2020. Promising and effective performance in low wind region is always desirable for small wind turbines. Multi rotor wind turbine with a number of small rotors on a tower is becoming a subject of interest among the researchers. Counter rotating horizontal axis wind turbine and unidirectional co-axial series rotor wind turbine are co-axial type multi rotor wind turbines. This work presents a comprehensive comparison of counter rotating horizontal axis wind turbine and dual rotor unidirectional co-axial series rotor wind turbine. This work discusses the different aspects such as concept of development, structural stability, design consideration, aerodynamics, wake considerations and power output performance of these wind turbines. Power performance curves are plotted by numerical method using MATLAB program for single rotor wind turbine, counter rotors wind turbine and unidirectional co-axial series rotors wind turbine. These power curves are analyzed and discussed in this paper.

CRWT, URWT, power, aerodynamics.