International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 9, September 2018, pp. 32–40, Article ID: IJMET_09_09_004 Available online at http://iaeme.com/Home/issue/IJMET?Volume=9&Issue=9 ISSN Print: 0976-6340 and ISSN Online: 0976-6359

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DESIGN AND IMPLEMENTATION OF FOR SEAMLESS ENERGY TAPPING USING RENEWABLE ENERGY SOURCES

Victor Du John H, Suriavel Rao R S and Dhanasekar S Department of Electronics and Communication Engineering Karunya Institute of Technology and Sciences, Coimbatore, India

ABSTRACT An integrated power system is one that uses two or more sources of energy to provide seamless power supply. In existing hybrid systems, normally tie-up of output energy is being done with a wind turbine acting as the primary producer and solar cells as its supplement, due to constraints of area and cost. Instead, tapping of the limited solar energy for another crucial purpose in the same system would have more merits. In normal wind turbines, the alternator field excitation shall be done either using a dc battery or by using a pair of permanent . The former has a setback that it has to use brushes and the latter loses its efficiency due to aging. Some ( less) use electronic circuits instead of brushes, which make the system bulkier with increased power ratings. We propose an idea by which the alternator field is excited using the solar power such that the above mentioned overheads are eliminated. Experimental results show that the proposed method yields improved power efficiency compared to the conventional approaches. Keywords: Solar power, Wind turbine, HAWT, VAWT, power efficiency Cite this Article: Victor Du John H, Suriavel Rao R S and Dhanasekar S, Design and Implementation of Alternator for Seamless Energy Tapping using Renewable Energy Sources, International Journal of Mechanical Engineering and Technology, 9(9), 2018, pp. 32–40. http://iaeme.com/Home/issue/IJMET?Volume=9&Issue=9

1. INTRODUCTION The source of power used to be fossil fuels so far which is now depleting at a faster rate than the expected. Moreover, their serious impact on the environment raises a question on their further use. Even though the world cannot snap off the usage of these fuels all abruptly, strategies are being devised to limit the use. One of the best solutions put forward was the switching over to non-conventional energy sources. These include wind and solar sources among numerous others. In fact, these two are the most extensively used non-conventional

http://iaeme.com/Home/journal/IJMET 32 [email protected] Design and Implementation of Alternator for Seamless Energy Tapping using Renewable Energy Sources sources compared to any other sources. Most of the existing wind turbines in India are Horizontal axis based. The generation of power using independent wind turbines is veryrare and these are also use horizontal axis. However the use of vertical axis based turbine isthe most suitable one for independent low power generation. This structure enables the mounting of a solar panel on its top so that a maximum absorbing capacity to solar radiation shall be achieved. This works on a simple principle that the solar panel which is the field-exciting source, rotates along with the prime mover of the alternator. In this case the solar power panel mounted on top of the wind turbine rotates along with the turbine to continuously provide the field excitation. The DC supply from the solar panel is taken using wires andthrough grooves in the shaft [2]. This supply is used to excite the field of the rotating field type alternator. The block diagram of the system is shown in fig. 1.1.The inner bold lines correspond to the electrical connections while the outer dotted lines mark the mechanical connections. The solar panel connects to the rotating field through the vertical type wind turbine. On the other hand, the vertical axis wind turbine supports the simultaneous rotation of the turbine along with another load like a solar panel mounted on its top surface. This leads to the utility of multiple energy sources at a time. The terminal voltage of the alternator is given to AC voltage regulator. Wind and solar energies are unpredictable. As the wind speed varies, the output voltage also varies accordingly [3]. Hence a voltage regulator with a battery backup is necessary to connect the system to various loads. The description of each part is elucidated in the following section.

2. WIND TURBINES

2.1. HORIZONTAL AXIS WIND TURBINES (HAWT) A wind turbine is a mechanical structure that rotates in accordance with the velocity of air speed due to the blade connected with it. If the rotation is supports power generation the is known as a wind power generator. Turbines with horizontal axis blades has advantages of greater stability and wing wrap, i.e., to cover the entire blade diameter by wind, thus allowing the turbine to collect maximum amount of wind energy in a day.

Figure 2.1 Block diagram of proposed power system All HAWTs have a huge tower structure, since the wind speed increases by 20% for every 10m height and thereby increasing the power output by 34%. Most of the HAWTs are self- starting and cheaper, instead a bulk amount of power (MW) can be generated with such large utilization of area. Some of the disadvantages of horizontal axis wind turbines are like requirement of several acres of land to install two to three HAWTs and such tall HAWTs are difficult to erect, needing very tall and expensive cranes and skilled operators which increases the cost. Moreover, as the wind direction changes the anemometer has to signal the

http://iaeme.com/Home/journal/IJMET 33 [email protected] Victor Du John H, Suriavel Rao R S and Dhanasekar S servomotor to reverse the blade rotation and it may fail at times. It is noticed that the horizontal-axis wind turbine has complex aerodynamic characteristics. The impact of air flow at the blades is different from that of the farther points, resulting variable speeds. Drag effects of wind speed also deflects the turbine blade direction and hence the efficiency.

2.1. Vertical Axis Wind Turbine (VAWT) As the name implies, these VAWTs have the main shaft vertically positioned [1], thus the generator and gear box can be mounted on the ground or closer to it such that it does not require any tower kind of structure unlike the HAWT and the turbine need not expose itself to the wind. These types of wind turbines employ high value of airfoil pitch angle yielding better aerodynamics while minimizing the drag at low and high pressures. But the limiting factor is the pulsating torque, which occur during the rotation of the turbine and creating drag with the wind. As the height increases, it becomes complex to install VAWT which means it shall work on a slow speed and less turbulent air just above the ground surface, thus reducing the conversion efficiency on the contrary.

Figure 2.2 Sample VAWTs (courtesy: Wikipedia) There are different types of VAWT such as Darrieus wind turbine, Savonius wind turbine, Egg beater wind turbine, Giromill wind turbine, Gorlov wind turbine and etc. are being used in different geography depending on the wind characteristics.

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3. POWER CONVERSION Although the ideal power values are high the actual power that can be obtained is significantly lesser. The actual power output of the turbine is dependent on many factors like the machine [4] and rotor type, the blade shape, and other loss factors. According to Albert Betz (1919), a German scientist, all wind turbines produce efficiency equal to or less than 16/27 (59.3%) only. This number is a globally accepted physical limit of power efficiency of a wind power system till today. It is the Betz limit otherwise Betz' law. Thus the value 0.59 is the “power coefficient” of wind power system and is defined as Cpmax = 0.59. In fact, practical wind power mills always operate below this limit. In fact, the Cp value is always unique as per the turbine type and wind speed. It is found that, with the best blade design, the power coefficient shall be around 0.35 to 0.45 only. By taking other components of the wind mill such as the gear box, ball bearings, and etc., into account, usable electricity lies in the range of 10% to 30% only [14] [6]. The wind power is

 (1)             where,

Pwind is wind power (W)

Cp is the performance coefficient of wind turbine In VAWT, the power calculation is different due to the swept area. Here the swept area is calculated by multiplying the height and diameter of its blade as,

Area, A = h x d (2) in which, h = turbine height (m) d = turbine diameter (m) So the VAWT output is

 (3)               where,

Pwind is wind power (W) ρ is the air density (kg/m3) V is the wind velocity (m/s) The project is on VAWT to gain improved performance against HAWT in case of power supply for individual houses or a street. In case of wind power generation in houses, vertical axis wind turbine occupies less area. Moreover, it is vertically symmetric in design as it rotates in one direction independent of wind direction. It has an added advantage that numerous vertical axis wind turbines can be arranged one after the other on a building roof, so that air hitting on first turbine will continue its flow to hit the turbine placed next to it and goes on. This shall improve the efficiency significantly but incur additional cost.

4. SYSTEM INTEGRATION As seen from the fig 4.1, that solar panel and wind blades are on same shaft (hollow), which is in turn connected to the rotor shaft of the alternator. As the wind turbine rotates, the solar panel also rotates along with it. The rotor bearing at the bottom is subjected to more stress as the entire solar panel set up and wind blade rest on it. Due to unequal drags on the blades [5],

http://iaeme.com/Home/journal/IJMET 35 [email protected] Victor Du John H, Suriavel Rao R S and Dhanasekar S the weight of the solar panel at the top surface and increased height of the shaft, the whole system undergoes vibrations which lead to physical instability. In order to overcome this problem an additional bearing on top with pole mounting (fig. 3.3) on three sides is provided to hold the top bearing in position and to reduce the stress on bottom bearing. Thus, during the rotation, the supports hold the center shaft tightly in position preventing vibrations.When the wind turbine starts rotating; the solar energy is connected to the field of the alternator which gives the final output. Alternators are rotating mechanical structures designed to generate ac power. An alternator converts mechanical rotations from diesel run engines, steam from boilers, or hydro turbines in to electrical energy. Currently, another source of power generation is identified as the wind. Because of the solar energy used to excite the field, the role of slip rings and brushes are eliminated in the alternators. In conventional rotating field supply, excitation is applied through carbon brushes.Here the exciting source, the solar panel rotates along with the rotor enabling continuous field excitation. But the shaft and the rotor must have a space across which the excitation is created.

Figure 4.1 Schematic diagram and rotor design The objective here is the design of alternator‟s rotor and shaft. The rotor design is as shown in fig. 4.3. It is a pole wound rotor with 8 poles. The availability of stampings for such size and saliency are rare. Hence we milled a solid mild steel rod to the required dimensions. The output voltage depends on the flux in the rotor and the flux in turn depends on the number of turns N and current Iof the windings. The coil current depends on the rating of the solar panel as it feeds thearmature field. To increase the output voltage, the numbers of turns of coil are increased. This demands a maximum slot area. The windings are made up of 29 gauge insulated-copper. For high rating alternators, stampings might beavailable and hence it will not be a problem to design the alternator. Even in such cases optimum area must be provided for better output. The second challenge of the alternator design is the selection of ball bearings. Due to the vertical erection and immense weight of the upper mounted components as in fig 4.1, the strength of the ball bearing shall be considered to make a friction free operation. As the design was for low power rating the above challenge was solved by simply mounting the low weight setup on a stand which lifted the alternator above the floor by a small height. But in case of larger alternators this challenge can be tackled by using thrust bearings, which pass the weight to the ground (support) while the rotation is on goingin the

http://iaeme.com/Home/journal/IJMET 36 [email protected] Design and Implementation of Alternator for Seamless Energy Tapping using Renewable Energy Sources inner ring. This is supported by conical rings and cylindrical balls. By combining the solar panel design along with the conventional permanent alternator an increased the flux in the air gap shall be achieved along with the option of extracting power during the absence of sunlight. The conversion is also made easy.

4.1. OUTPUT POWER So with the available wind power, the maximum power that be taken out depends on generator efficiency. The power output equation of generator,

     (4) where, P is power (W), η is efficiency of generator

4.2. RESULTS AND DISCUSSION The following section has the design and calculations of wind to electric conversion and output efficiency.

Figure 4.2 Implemented prototype Figure 4.3 Blade dimensions

Table 4.1 Design Specifications Area of wind blade 75 sq. ft. Height of wind turbine blade 8.3 ft. Diameter 9 ft. Actual diameter (due to bending of blades) 5 ft. Area = height * diameter 3.845 sq. m Air density 1.225 kg/m3 Performance co-efficient, Cp 0.30 Velocity 5 m/sec 3 Power in wind = 0.5*Cp*area*velocity =0.5*0.3*3.845*53 = 72.094 W For30% alternator efficiency, Output power = 21.628 W

The value of Cp(ranges from 0.3 to 0.45) depends on the design of blades.

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Assume average wind speed as 5m/s Here Constant, C =0.5*area*velocity3=240.313

In this design range of Cp is about 0.30 - 0.45

Table 4.2 Wind power calculation Constant, C Cp Wind Power(W) 240.313 0.30 72.094 240.313 0.35 84.109 240.313 0.38 91.32 240.313 0.4 96.12 240.313 0.42 100.9 240.313 0.45 108.14 In this alternator design, efficiency is about 20%-50%.

For Cp=0.30, the output power for different alternator efficiencies are given below in table 4.2.

Table 4.3 Wind power conversion for Cp = 0.30 Wind Power (W) Alternator Efficiency Output Power (W) 72.094 0.20 10.419 72.094 0.30 21.628 72.094 0.40 28.834 72.094 0.50 36.047

For Cp=0.35, the output power for different alternator efficiencies are given below.

Table 4.4 Wind power conversion for Cp = 0.35 Wind Power (W) Alternator Efficiency Output Power (W) 84.109 0.20 16.823 84.109 0.30 25.233 84.109 0.40 33.644 84.109 0.50 42.055

Figure 4.4 Wind power versus Cp with C = 240.313

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Figure 4.5 Power conversion with wind power = 72.094 and Cp = 0.3

Figure 4.6 Power conversion with wind power = 84.109 and C p = 0.35 The performance plots shown above reveal the efficiency variation with respect to varying wind power and different Cp, the performance coefficient.

CONCLUSION The mechanical components and hardware used in the project are all realistic. The solar energy is widely used across the world as an alternative source of energy. The dimensions and approachof the systems may look different whereas the architecture remains the same. The concept of vertical axis wind turbine is very popular in Europe and USA. Most of the independent and grid feeding type of natural power sources employ vertical axis wind turbines (VAWT). In our work, the novelty lies with the linking of solar current to excite the field of the alternator instead of using other dc power source. There is also a controversy over calling this system as a „hybrid system‟ because such a system should tap power from two or more systems and couple to loads. Hence the name integrated system has been preferred. But in this system, the loads are supplied only from the power generated from the wind turbine. The conclusion is that the effective use of non-conventional resources to tap energy is on a huge demand since the conventional sources are depleting at a fast pace. Hence the need of the hour is to maximize the energy production from such sources to promote green and clean energy. This idea is aimed at implementing a green energy system with eco-friendly approach at a small level to create awareness on go green agenda.

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