Evaluation of different size savoniuswind turbines for water pumping

Abstract

Wind is one of the renewable energy sources that Ethiopia is endowed with, despite it hasbeen nearly untapped for various purposes. Utilization of this ample energy source to runwind turbine for the purpose of water pumping is can be considered effective from theperspective of cost required to purchase diesel engine to operate pumps, environmentalfriendly and accessible to remote areas far from power transmission lines. In this study,four savonius wind turbines of different diameters with uniform turbine height (1m) weredesigned on the basis of Adama’s town wind analysis with the presumable dischargecapacities and the experiment was laid out in RCBD. The experiment was conducted inMarch, April and May 2019. The result of the experiment showed that except the largestturbine where the rotor diameter is 1.3m, the rest of the turbines could not pump water fora total head of 7m. The ANOVA showed that there was significant effect of turbinediameters (P<0.05) on power coefficient, pumping power, tip speed ratio and discharge.The largest turbine capable to discharge a maximum discharge of 0.036 lit/s andminimum discharge of 0.004lit/s for wind speed ranging from 2.49m/s to 3.77m/s duringthe experiment. The result of this study depicted that the estimated average powercoefficient, tip speed ratio and pumping power of the largest turbine are 0.07, 1.04 and1.7 watts respectively. On the other hand wind speed variation had less significant effect(P<0.05) on the variation of power coefficient, pumping power, tip speed ratio anddischarge. According to regression analysis (P<0.05), the variation of power coefficient,pumping power, tip speed ratio and discharge significantly (98%, 98.7% , 91.6% and99% respectively) attributed to the change in wind speed. Furthermore, the variation indischarge is highly (85.2%) attributed to RPM of the turbine (P<0.0%). Hence, toimprove the discharge capacity of the largest turbine use of speed up gear ratio can beconsidered as one best alternative in addition to improvement in manufacturing of ropeand washer pump. On the other hand, variation of turbine height (4-10m) has less effecton pumping power consequently on discharge. However, prediction of discharge fordifferent speed up gear ratios has significant effect on discharge. Accordingly for windspeed 3.1m/s where the pump can operate for 107 days, if the speed of the pumpingiiwheel is three times that of the turbine, the system can discharge 0.047lit/s which is evenmore than the design discharge.