Modification of the Vertical Axis with Variations in the Number of Blades of the Savonius Wind Turbine

--The potential wind speed in Indonesia is generally low at 3 m/s to 7 m/s, so this type of vertical axis turbine is considered very suitable for use in wind conditions in Indonesia. There are several types of vertical-axis wind turbines. One type of vertical axis wind turbine is the Savonius wind turbine. This type of wind turbine has many advantages, such as receiving wind from all directions, being easy and cheap to manufacture, and rotating at a relatively low angular speed. This test was carried out to determine the performance of conventional and modified Savonius turbines with 2 and 3 blades variables in each turbine blade shape. The modification is made by changing the shape of the blade twisting by 45o. The turbine is carried out on a laboratory scale with a wind source using a fan directly opposite the turbine. The results showed that the highest turbine power occurred in a modified 2-blade turbine, namely 1.88 Watt with a torque value of 0.04 Nm and a shaft rotation of 450 rpm. 2 modified blades also obtain the highest rotation value at a wind speed of 6 m/s producing 896 rpm. However, the highest torque value is obtained by a conventional 2-blade turbine with a value of 0.136 Nm. A modified two-blade turbine receives the highest efficiency in each turbine, with an efficiency value of 36.92%. In comparison, the highest turbine efficiency for a modified 3-blade turbine reaches 11.69%, considered less efficient than other turbines.


I. INTRODUCTION
Various levels of society need electrical energy. A power generation system can generate this electrical energy. However, most of the fuel to generate electricity still uses fossil fuels which are non-renewable fuels. Besides the longterm impact of using fossil energy is global warming, alternative energy sources are needed [1,2].
With the depletion of fossil energy reserves, we need to think about alternative energy sources. By considering renewable energy as an energy source [3]. Given the geographical conditions of Indonesia, which has natural resources with good potential for developing new renewable energy sources, one of which is wind [4][5][6].
Wind energy can be used as an energy source by using wind turbines. A wind turbine is a device used to convert kinetic energy into mechanical energy (torque and rotation), which will convert mechanical energy into electrical energy using a generator.
There are two types of wind turbines: vertical-axis wind turbines and horizontal-axis wind turbines. The potential for wind speed in Indonesia is generally low at 3 m/s to 7 m/s, so the vertical axis turbine type is considered very suitable for use in wind conditions in Indonesia [7]. There are several types of vertical-axis wind turbines. The Savonius wind turbine is a vertical-axis wind turbine [8].
Many advantages this type of wind turbine has, such as being able to receive wind from all directions, being accessible and cheap to manufacture, and can rotate at a relatively low angular speed. However, the standard design of the Savonius type still has low efficiency compared to other kinds of vertical-axis wind turbines [9,10].
Several researchers have conducted experimental studies by modifying the standard design. The improvements started from changing the shape of the blades to adding several components, and several modifications were made to increase the angular speed and maximum torque that the Savonius turbine could produce. In this work [11], an experiment was carried out to determine the most effective operating parameters, and two blade rotors were more efficient. Research [12] discusses improving the performance of the Savonius turbine by optimizing the effect of different geometric parameters and by developing new designs, resulting in an increase in the performance coefficient of 27.3% compared to conventional rotors. This study discusses further studies to determine the effect of variations in the number of blades on the performance of the Savonius rotor wind turbine.

II. FUNDAMENTAL THEORY A. Wind Power
The wind is the air that moves due to differences in pressure on the earth's surface. Wind moves from an area of high pressure to a place of lower pressure. The wind that blows on the earth's surface occurs due to differences in solar radiation receivers, resulting in differences in air temperature. The difference in temperature causes a pressure difference, eventually causing air movement [13].

B. Turbine Cross-sectional Area
The cross-sectional area of the turbine is the effective area of the wind turbine blade capable of receiving kinetic energy from the wind and converting it into mechanical energy [15]. For the Savonius type, the cross-sectional area of this turbine is expressed in Equation 2. = (2) H is the height of the wind turbine, and D is the diameter of the wind turbine.

C. Tip Speed Ratio
Tip Speed Ratio (TSR) is the ratio of the tip speed of the rotor to the wind speed. The TSR value can be calculated by equation 3 [16]. TSR =  = (3) v is the airspeed (m/s), ω is the angular velocity (rad/sec), and r is the turbine radius (m).

D. The Angular Velocity
The angular speed is the blade tip speed concerning one shaft rotation per second, shown in Equation 4.
 is the angular speed (rad/s) and n is the rotor speed (rpm).

E. Turbine Power
Turbine power is the power generated by the turbine due to the wind hitting the blade so that the tip of the blade starts to move in a circle, as shown in Equation 5. = (5) is the power generated by the turbine (watts), T is the torque (Nm), and ω is the angular velocity (rad/second).

F. Torque
The torque coefficient can be calculated using equation 6. = = (6) T is torque (Nm), F is force (N), r is the pulley radius (m), m is the loading mass (kg), and g is gravity (m/s 2 ).

H. Daya Generator
Generator power can be calculated by equation 8. Pg = V . I (8) V is Voltage (Volt) and I is Current (Ampere)

I. Savonius Turbine
Wind turbines were first discovered in Finland by a Finnish scholar named Sigurd J. Savonius in 1922 and are Sshaped when viewed from above. This type of turbine generally moves slower than the horizontal axis wind turbine type but produces large torque. The turbine construction is straightforward, consisting of two half-cylinder blades. [17].
During its development, the Savonius turbine underwent many changes in the shape of the blades. One of the parameters that significantly affect the Savonius-type wind turbine's total performance is the blades' shape or design. In general, the forms that have been researched and used to date are: Semi-circular (Semi-circular) Figure 1. Semi-circular shape [18] This is the most common and frequently used form. The construction is straightforward, only using a cylinder split in half and arranged according to the shape of the letter 'S [19]. Figure 2. Helical bucket shape [18] The spiral shape performs similarly to adding multiple stages to the rotor. The moment oscillation when operating using a helical rotor is significantly reduced. Based on research, the winding performance is not much different from the semicircular profile performance [20]. The rotor with bucket twist produces a more significant moment than the semi-circular profile bucket. [21], obtained a Cp value of 0.31 for a rotor with a bucket twist and 0.29 for a semi-circular. Below, plotting twist angle vs torque, we can note that the angle value that produces the highest torque is 45˚ [22].

A. Design Stage
The design stage is a process for designing and designing the tools to be made. Making a design pattern for the devices is the first step to making it easier to develop tools according to the desired position and location. The test scheme can be seen as follows. Judging from the test scheme above, it can be described in the Savonius turbine test as follows.

B. Test
The testing steps, namely: 1. Prepare the necessary equipment 2. Ensure that the tools used are properly connected to each other 3. Ensure the turbine rotates properly 4. Ensure that the generator coupler is properly installed 5. Turn on the fan 6. Carry out the testing process 7. Vary the wind speed 8. Varying lamp load 9. Recording output data and other data 10. Repeat Steps 5-9 varying the turbine and lamp load 11. Testing completed IV. RESULTS AND DISCUSSION In this study, tests were carried out to obtain the performance of the Savonius turbine with variations of the turbine blades of 2 conventional blades, two modified blades, three conventional blades, and three modified blades and modified savonius turbine with a torsion angle of 45°. Figure  6 is the process of testing the tool. The wind speed used comes from a 50cm diameter fan by varying the wind speed of the turbine to be tested with wind speed 1, which is 4.2 m/s, wind speed 2 is 5.5 m/s, and wind speed 3 is 6 m/s. Fan placement can be seen in the test scheme with a position perpendicular to the turbine to be tested. Each turbine's electrical load testing variable uses 6 pcs 3-watt lamps, with a total lamp load of around 18 watts. In trying the Savonius wind turbine with turbine variations, several data collections were carried out to measure the performance of each turbine. The test results are obtained as follows. The wind power generated by the fan at the wind speed variation of the turbine under test is: 1. Wind speed 1 = 1,2 / 3 = 0,0375 2 = 4,2 m/s =       Figure 9 shows the relationship between shaft rotation and electric power with load variations. Based on the chart above, it can be seen that the largest electric power is generated at a load of 3 Watt, namely 147 mW, shaft speed is 248 rpm with a wind speed of 6 m/s while the lowest electric power is generated at 18 Watt load 56.24 mW, shaft speed is 179 rpm with a speed of 179 rpm. The most downwind is 4.2 m/s. This is because the shaft speed decreases with the increasing load applied and increases with increasing wind speed.  The picture shows the relationship between shaft rotation and electrical power with load variations. Based on the chart above, it can be seen that the largest electric power is generated at a load of 3 Watt, namely 74.52 mW, the shaft speed is 208 rpm with a wind speed of 6 m/s. In comparison, the lowest electric power is generated at a load of 18 Watt 12 mW. The shaft speed is 142 rpm, with a rate of the most downwind is 4.2 m/s. This is because the shaft speed decreases with the increasing load applied and increases with increasing wind speed.
Journal of Advanced Technology and Multidiscipline (JATM) Vol. 02, No. 01, 2023, pp. 01-08 e-ISSN: 2964-6162 8 Figure 12. Graph of the relationship between efficiency and tordque with variations in wind turbine blades The picture is a graph of the relationship between efficiency and torque. Based on the chart above, it can be seen that the initial torque value is the highest on the modified two-blade turbine, but in the end, the conventional two-blade turbine remains higher. The highest efficiency value is two modified blades with an efficiency value of 36.92%, and the lowest is three modified blades with an efficiency value of 9.85%.

V. CONCLUSION
Based on the results of the research on the design of the two-blade wind turbine rotor made, the turbine with the highest efficiency value, namely two modified blades, reached 36.92% with a torque value of 0.040 Nm and a shaft rotation of 450 rpm at a wind speed of 6 m/s and a loading of 160 g. The turbine power generated under these conditions is 1.88 mW. In comparison, the efficiency of the modified 3blade turbine only reaches 11.69% with a torque value of 0.037 Nm and a shaft rotation of 152 rpm at the same wind speed with a loading of 150 g and turbine power generated is 0.59 mW.