Additional guide vane (GV) to the Savonius rotor is used to overcome the low rotor efficiency. This study is experimentally carried out to know the influence of guide vane in improving two blades Savonius rotor performance. There were four designs of guide vane which are 4, 5, 6 blades and installed at different tilt angles, which were 0 • , 20 • , 40 • , and 60 • . The experiment was done under wind speed of 5.9 m/s, 7.0 m/s, 8.1 m/s, 9.3 m/s and 10.4 m/s. The results show that the 6 blades of

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... GV at a 60 • tilt angle attained the best Cp, which was 0.0279 at the tip speed ratio of 0.53. The Cp increased up to 40% with six blades of GV. Wind direction identified significantly affected the rotor performance. The rotor performed best on the wind direction of 0 • attained Cp of 0.079, but when the wind direction was modified on 30 • , the rotor with 6 GV attained Cp of 0.0153 did not perform better than without GV that produced Cp of 0.0166. The guide vanes improve the Savonius rotor performance compared to the rotor without a guide vane. However, the wind direction also needs to be considered no less important factor affecting the Savonius rotor performance.