The present investigation is aimed at exploring the feasibility of Savonius wind turbine blades for power generation, which has hitherto been limited to water pumping and grain grinding work. In this project, an attempt has been made to develop a twisted blade for its use in Savonius wind turbine rotors. The objective is to reduce the negative torque and the self-starting characteristics of a single stacked rotor system while maintaining a high rotational speed so that such a rotor system can be used for electricity generation. Tests have been carried out of semicircular (curved) and twisted blades both in a three bladed rotor system. Aerodynamic performance of these blades have been evaluated in a low speed wind tunnel on the basis of starting torque, power output and rotational speed at various setting angles and gap widths. Experimental investigation shows the potential of the twisted bladed rotor in terms of smooth running, higher coefficient of performance and self-starting capability as compared to that of the semicircular bladed rotor.

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Experimental Investigation of Twisted Bladed Savonius Wind Turbine Rotor

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 author researched on different technical design solutions and their advantages in terms of noise, shadows and impacts on birds and wildlife. The objectives of this research were thus to design and develop a Savonius rotor blade locally and compare its performance and production cost with the existing blades. From the developed blade, a laboratory test was conducted using a domestic fan and a torque of 15.46NM at a wind speed of 6.94 m/s was obtained which led to a conclusion that it was possible to locally develop a wind conversion technology that is affordable, efficient and adaptable for Kenya’s average wind speed of 4m/s.

Design and field testing of a Savonius wind pump’s rotor blade for pumping water in rural areas

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.

R. N. Clark

Papers

Wind turbines for irrigation pumping