Performance Analysis of 2 U-Type Savonius Blades for Vertical Rotor Wind Turbine

Renewable, unlimited and environmentally safe, wind energy is referred to as renewable energy. In Indonesia, wind speeds between 3 to 7 m/s are considered moderate wind speeds. Wind turbines can be used to convert wind energy into electrical energy. The Savonius rotor is cylindrical and has two or more blades attached. The purpose of this study is to determine the power, torque, and rotation per minute produced by a Savonius rotor wind turbine with a blade radius of 50 cm and a blade height of 100 cm. Wind speeds of 3 m/s, 5 m/s, 7 m/s, 9 m/s, 11 m/s, 13 m/s, and 15 m/s were used for testing. A tachometer was used to measure rpm, while a loadcell sensor measured torque and power data. Based on the research findings, it was found that each wind speed variation produced a different average rotor rotation per minute. The rotor speed, torque, and power increased with increasing wind speed.


Introduction
Due to the increasing cost of fossil fuels, abundant renewable energy sources become an alternative source for generating electricity that is environmentally friendly [1].One of the most promising and cleanest renewable energy sources is wind power.Indonesian wind speeds vary from 3 m/s to 6.3 m/s, based on Potential Energy Unit (PEU) statistics [2].Among the renewable energy sources are geothermal, solar, and wind energy.There are two types of wind turbines: vertical and horizontal.The former is better used at low wind speeds [3].
Senthilkumar et al. [4] state that vertical-axis wind turbines can be built and maintained more cheaply and efficiently than horizontal-axis wind turbines.The advantage of vertical wind turbines over horizontal-axis wind turbines is that they can generate energy at lower wind speeds [5].Furthermore, vertical-axis wind turbines have the benefit of horizontal-axis wind turbines in that they are simpler to construct and can capture wind from various directions [6] and lower cost to manufacture vertical axis wind turbines.Vertical axis wind turbines usually operate under constant wind conditions [7].
A suitable wind turbine development in Indonesia is the savonius vertical axis wind turbine due to the low average wind speed [8].Savonius wind turbines have high starting torque but are inefficient at low wind speeds [9].Savonius wind turbines are effective in extracting wind energy and generating mechanical and electrical energy from small scale i.e. household scale to large scale for utilities [10].Savonius wind turbines have drag, so they cannot spin faster than the wind speed.The drag and lift forces act on the turbine surface when the wind hits its convex or concave parts.Basically, the turbine rotates due to the different thrust forces between the convex and concave parts of the rotor.Therefore, the main driving force of the Savonius rotor is the thrust force [11].Wind turbines generate electrical energy by converting wind energy into mechanical energy.Savonius wind turbines consist of two cylindrical parts commonly called blades.Savonius wind turbines consist of a convex part and a concave part and when viewed like the letter S [12].

Time and Place of Research
This research was carried out from March 2023 to September 2023.Testing of the Savonius wind turbine was carried out at the Agricultural and Biosystem Engineering Workshop, Faculty of Agriculture and UPT Integrated Laboratory, Universitas Sumatera Utara.

Tools and materials
This research tool is an anemometer, multimeter and tachometer, screwdriver, drilling machine, welding tool, grinding machine, solder, tool keys, pliers, plastic box, ruler, plate as loadcell load, laptop, and stopwatch.
The materials of this research are 2 mm aluminum (1 m x 2 m) as many as 2 sheets, 3x3 cm angle iron with a thickness of 3 mm, pipe-shaped iron with a diameter of 4 cm with a thickness of 2 mm, 1 mm copper cable, 4 mm diameter bolts, 1 inch nails, bearings, sprockets, chain, DC generator maximum capacity 350 watts, tin, load cell, arduino mega, HX711, SD Card module, sd card, power bank, 1 kg loadcell, water as a load, water container, breadboard, arduino cable, generator capacitor, jumper cable, N52 magnet, and alteko glue.

Overview of the Design
This blade design description serves as a benchmark for the model to be made in research.This blade design will be adjusted based on the design results of the savonius rotor vertical wind turbine in previous studies In this treatment, the rpm, torque and turbine power generated by the 2-bladed U-type wind turbine will be analyzed with 3 samples for each treatment.
3 2.5 Research procedure 2.5.1 Savonius Wind Turbine Design.The blade formation is measured first on the material used, namely aluminum with a thickness of 2 mm, after that the aluminum is cut according to size, the aluminum will be given pressure so that it can be bent according to the blade type, namely U.And on the savonius wind turbine shaft which has been previously designed, a hole will be made to make a blade holder according to the number of blades, namely 2 blades.

Savonius 2 Blade Wind Turbine
Testing.At this stage, testing was carried out at a water level of 6 cm.The following are the test steps:  Preparing a 2-bladed U-shaped savonius wind turbine. Prepare the circuit and arduino-based firmware program as a savonius wind turbine torque measuring device in the proteus application. Installing the arduino circuit on the Savonius wind turbine. Making sure the sensor is connected to the arduino properly. Calibrating the loadcell sensor on the Arduino as a torque meter to get accurate results. Connecting the power cable from the power bank to the microusb. Filling water at a water level of 6 cm. Set a distance of one meter between the blower and the wind turbine. Set the wind speed according to the wind speed variation used, namely 3 m/s, 5 m/s, 7 m/s, 9 m/s, 11 m/s, 13 m/s, and 15 m/s. Turning on the blower and taking rpm data is done manually, namely counting every rotation that occurs during the initial 1 minute. The data collection process lasts for 2 minutes and after 2 minutes, turn off the blower, unplug the power cable from the powerbank. Then remove the sd card on the arduino module and move the txt data to excel. Repeating the above steps according to the wind speed variations, namely 3 m/s, 5 m/s, 7 m/s, 9 m/s, 11 m/s, 13 m/s and 15 m/s for torque and rpm data collection.

Research result
Experimental results on the rotation speed of the turbine rotor due to varying wind speeds can be presented in the following Table 1.Table 1 shows that the turbine rotation speed increases as the wind speed becomes higher.The resulting average maximum rotation speed is at a wind speed of 15 m/s with an average rpm of 121 rpm or 2,017 rps, while at the lowest wind speed of 3 m/s it produces an average of 35 rpm or 0.583 rps.The faster the wind speed, the faster the turbine rotor rotates.
In Figure 2, wind speed has an increasing effect on the rotation of the turbine shaft, this occurs because there is an increase in air mass per second which pushes the turbine rotor blades so that the rotation tends to increase.From this, an Anova statistical test was carried out which showed that each variation in wind speed had an effect on the rotation of the Savonius wind turbine shaft.The following data is in Table 2. From the statistical test, Fhit is greater than Ftab, which means that each additional wind speed affects the rpm Savonius wind turbines produce them.In addition, the parameter measured in this study is Savonius wind turbine produces torque.Table 3 shows that torque increases with increasing wind speed.The average maximum torque generated is at a wind speed of 15 m/s with an average of 0.106 Nm, while the average torque generated at the lowest wind speed of 3 m/s is 0.042 Nm.

Figure 3. The relationship between wind speed and turbine rotor torque
In Figure 3, the torque produced by the Savonius wind turbine is strongly influenced by the wind speed.The Savonius wind turbine produces torque that increases from the lowest wind speed of 3 m/s to the highest wind speed of 15 m/s, with the highest torque of 0.106 Nm and the lowest torque of 0.042 Nm.
From this, a statistical test is carried out which shows that each variation in wind speed has an influence on Savonius wind turbine produces torque.The following data is in Table 4.
From the statistical test, Fhit is greater than Ftab, which means that each additional wind speed affects the torque produced by the Savonius wind turbine.
In addition, the parameter measured in this study is the turbine power generated by the Savonius wind turbine.Table 5 shows that the power produced by the Savonius wind turbine increases with increasing wind speed.The average maximum power produced is at a wind speed of 15 m/s with an average of 749.495Nm/s.In Figure 4, wind speed has an influence on the power produced by the Savonius wind turbine.Power increases with increasing wind speed.This is because wind speed increases electrical power.At a wind speed of 15 m/s, the highest electrical power reached 749.495Nm/s, and at a wind speed of 3 m/s, the lowest electrical power was 119.387Nm/s.
From this, a statistical test is carried out which shows that each variation in wind speed has an influence on the torque produced by the Savonius wind turbine.The following data is in table 6.

Conclusion
Based on the results and discussion, it can be concluded that wind speed affects Rpm, torque and power generated.Rpm, torque and power also increases with higher wind speeds.In this Savonius 2 blade wind turbine, the highest rpm, torque and power are produced at a wind speed of 15 m/s with an average turbine rotation speed of 121 rpm or 2,017 rps, an average torque of 0.106 Nm, and an average power output of 749.495Nm/s .

Figure 4 .
Figure 4.The relationship between wind speed and turbine power

Table 2 .
Anova analysis of wind speed on turbine shaft rotation

Table 4 .
Anova analysis of wind speed on torque

Table 6 .
Anova analysis of wind speed on turbine power From the statistical test, Fhit is greater than Ftab, which means that each additional wind speed affects the turbine power generated by the Savonius wind turbine.
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