Design and Testing of a Low Cost and Higher Efficient Savonius Wind Turbine’s Rotor Blade for Low Wind Speed Applications

Abstract

Studies indicate that vertical axis wind turbines provide a more reliable energy conversion technology as compared to horizontal axis wind turbines, especially in areas of lowly rated and/or uncertain wind speeds. The challenge however is the development of an efficient Savonius rotor blade which is affordable to low income earners in Kenya. The different technical designs available in the local market were studied and their effects in terms of noise, shadows and impacts on birds and wildlife analyzed. The objectives of this research were thus to design and develop a Savonius rotor blade with locally available materials and compare its performance and production cost with the existing blades. The blades were made using glass reinforced fibre because of the material’s light weight. This factor enabled the rotor to rotate at very low wind speeds, it is also long lasting and does not rot hence can survive in all weather conditions. A prototype rotor blade was fabricated, tested and an efficiency of 29% was achieved. Further modification was done and a more efficient rotor blade was fabricated which achieved an efficiency of 45%. A maximum power output of 111.64 W at a wind speed of 8.57 m/s with line voltages of 75 V, 85 V, 81 V and currents of 0.68 A, 0.88 A and 0.85 A respectively for line L1, L2 and L3 were obtained when the blade was connected to a three phase generator. The line voltages and currents obtained were with a torque of 143.8 N-m. A field test was also done at Ngong hills at a height of 2460m (8070 ft) above the sea level and a maximum wind speed of 6.44 m/s was reached at the time of testing. Voltage and current linesof 57.6 V, 57.98 V, 57.60 V and 0.88 A, 0.90 A and 0.80 A were recorded for each line giving a maximum output power of 85.95 W. The Vac from the generator was then rectified by a bridge rectifier and a maximum voltage obtained was 10.5 Vdc which was then used to charge a 12 V dc lead battery. The battery was fully charged after 11 hours and 36 minutes and used to light a 12Vdc bulb for 7 hours. The total cost of developing the rotor blade was Kshs 79,800 which was found to be 58.5 % cheaper than rotor blades in the local market of the similar rating. The above tests led to a conclusion that it is possible to locally develop a wind conversion technology that is affordable, efficient and adaptable for Kenya’s average wind speed of 4 m/s.