An Experimental Investigation of a Savonius Wind Turbine Rotor Performance for Low Wind Speed Applications

Abstract

Designing and installation of wind turbine projects globally have boosted power supply to the national grid and other associated works, however, problems associated with the current small scale wind turbines include: High starting wind speed; high capital cost; poor after sales services and maintenance by the suppliers and also collapse of the hub as a result of the structural design. This research focussed on developing Savonius rotor blades using fibre reinforced glass which processes a characteristic of being very light, strong and durable. The generator part was also mounted on the ground which eliminates the collapse of the hub and at the same time easily accessible during maintenance. A field visit to the wind energy market stakeholders was conducted through a questionnaire hence analysis on the strength, weaknesses, opportunities and threats were done. After studying the market, design and development of two models of different power output was done. The models were designed with 2 blades of a semi-circular cross sectional profile, a separation gap of 0.03 m, aspect ratio of 2 and overlap ratio of positive 25%. For the first model upon testing with a direct drive generator, the cut-in-wind speed was found to be at 2.7 m/s which produced a mechanical power of 14.9 N and electrical power of 1.1 W. At the rated wind speed of 7.5 m/s, the power output obtained was 23.32 W instead of the theoretical power of 56.9 W which resulted to a performance (efficiency) of 13%. The second model upon testing, the cut-in- wind speed was found to be below 2.5 m/s since at 2.1 m/s a mechanical power of 11.2 N and electrical power of 242.2 W was obtained at the rated wind speed of 7.5 m/s instead of the theoretical output of 259.9 W which resulted to a performance of 28%.The second prototype was then tested at Ngong’ hills (Kajiado county) and it was found that at 1.53 m/s, 0.7 W was obtained. The rated wind speed was not attained on the day of testing but the power output at the highest measured wind speed of 6.44 m/s was 228.2 W which resulted to a performance of 44%.The above results led to a conclusion that it is possible to locally develop a wind turbine rotor blades (in a local workshop with locally available tools and materials), that is more efficient and adaptable for Kenya’s average wind speed of 4 m/s.