Oct 3, 2015 - construction processes included the blades, nose, casing, tail, tower, etc. .... Other advantages of fiberglass are its relatively low-cost, long.
"Design, Construction and Testing of Low-Cost SmallScale Horizontal Wind Turbine"
Ahmed F. Abdel Gawad, and Amel Farouk
The First Conference of "Recent Trends in Energy Systems (RTES)"
Organizer: Benha University
Cairo, Egypt
3 October, 2015
Design, Construction and Testing of Low-Cost Small-Scale Horizontal Wind Turbine Ahmed F. Abdel Gawad*, Amel Farouk** *Professor of Computational Fluid Mechanics, Mech. Power Eng. Dept., Faculty of Eng., Zagazig Univ., Egypt **Professor, Electrical Power Engineering Dept., Faculty of Engineering, Zagazig University, Egypt
Abstract The basic idea of this paper is to construct a low-cost wind turbine. The turbine can be used for home-scale applications at least to cover part of the electricity consumption. Thus, the saved money can be direct to other interests of the family. At the same time, this small turbine can be considered as a model to evaluate the performance of large-scale turbines for commercial use. The model is a horizontal-axis wind turbine. The design and construction processes included the blades, nose, casing, tail, tower, etc. The model was tested at suitable locations; "El-Hadda Mountain" and "Jeddah coast". 1. Importance First use of wind power was to sail boats in the Nile some 5000 years ago. Europeans used wind mills to grind grains and pump water in the 1700s and 1800s. First windmill to generate electricity in the rural USA was installed in 1890. Today, large wind-power plants are competing with electric utilities in supplying economical clean power in many parts of the world [1]. Nowadays, there is a global interest in finding new energy sources due to the quick consumption of petroleum (main source of energy). It is expected to consume all the global reservations of petroleum in about sixty years. Meanwhile, earth population is expected to reach 12 billions by 2050. Thus, the need of energy will be multiplied by a factor of eight by 2050. The new sources include wind, solar, biogas, biomass, tidal, marine waves, and marine current energies. Wind energy is the most growing of all these energies in the world. 2. Idea The idea concentrates on the construction of a low-cost wind turbine. The turbine is suitable for home-scale applications at least to cover part of the electricity consumption. The money saving may be direct to other interests of the family. Moreover, this small turbine can be considered as a model to evaluate the performance of large-scale turbines for commercial usage. A model of a horizontal-axis wind turbine (HAWT) is considered in the present study. The validity of the turbine is to be confirmed through field tests in suitable locations. The turbine and its components must be simple in design, manufacturing, assembly, and operation.
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3. Wind Turbines Wind energy is the kinetic energy of the air in motion. A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator. The two main types of wind turbines are the horizontal-axis wind turbine (HAWT) and vertical-axis wind turbine (VAWAT), Fig. 1.
Fig. 1 The two types of wind turbines [2]. The components of the horizontal-axis wind turbine (HAWT) are shown in Fig. 2. Based on Fig. 2, the main components that are to be considered in a simple HAWT can be listed as: blades, rotor, shaft, simple transmission, generator, vane nacelle (casing), and tower. The small-scale wind turbines (HAWT and VAWT) were investigated by many researchers as can be seen in Refs. [3-12]. Figure 3 shows two examples of home-made wind turbines. The output power of such turbines may vary from 30 Watts to 1200 Watts.
Fig. 2 Components of horizontal-axis wind turbine (HAWT) [2]. 2
(a) [13] (b) [14] Fig. 3 Two examples of home-made HAWT turbines. 4. Present Model 4.1 Model specifications The specifications of the present HAWT turbine model can be listed as: Type
: 3 Blade, Upwind
Rotor diameter
: 1.2 m
Tower height
: 2.5 m
Type of blades
: Tapered with standard NACA 2412 section
Blade pitch control
: None, Fixed Pitch
Start-up wind speed
: 5.0 m/s
Rated wind speed
: 8.0 m/s
Cut-out wind speed
: None
Furling wind speed
: 13.0 m/s
Rated power Transmission
: 400 Watts : Simple two-gear mechanism
4.2 Model construction The construction of the different components of the present HAWT model is based on the knowledge and data of Refs. [13-18]. 4.2.1 Rotor design The rotor is a three-blade type which is known with its high efficiency and balance. It has a tip speed-ratio of 6 to 7, Fig. 4. Tip speed-ratio is the ratio between the speed of the blade tip and the speed of the wind.
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Fig. 4 Three-blade rotor of present model. 4.2.2 Blade section The standard airfoil section of NACA 2412 is considered. It has a maximum camber of 2% located 40% (0.4 chord) from the leading edge with a maximum thickness of 12% of the chord. Fig. 5. This section was recommended by many researchers [16-18] for wind turbine applications.
Fig. 5 Airfoil section of NACA 2412. Both uniform and tapered blades were manufactured, Fig. 6. The tapered blades, Fig. 7, were used in the field tests as they had much better performance than the uniform blades.
Fig. 6 Uniform and Tapered blades. 4
Fig. 7 Tapered blade with holder. 4.2.3 Blade material The blades were made of fiberglass, Fig. 8, because it has low rotational inertia, which means that wind turbine can accelerate quickly if the wind picks up, keeping the tip speed ratio more nearly constant. Operating closer to optimal tip speed ratio during energetic gusts of wind allows wind turbines to improve energy capture from sudden gusts that are typical in urban settings. Other advantages of fiberglass are its relatively low-cost, long operational-life, and resistibility to environmental conditions.
Fig. 8 Layers of fiberglass. 4.2.4 Head The function of the head, Fig. 9, is to connect turbine blades with the nose and generator shaft. It was made of Aluminum because of its light weight, proper stiffness and low cost. The head has three threaded holes for the fixation of blades.
Fig. 9 Turbine head.
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4.2.5 Nose Considering the aerodynamic design of the nose section of any body in a moving fluid, an important problem is the determination of the nose geometrical shape for optimum performance. For many applications, such a task requires the definition of a solid of revolution shape that experiences minimal resistance to rapid motion through such a fluid medium. The main two tasks of the nose are to deflect air towards the turbine blades and avoiding stagnation at the turbine head. Generally, turbine nose may take one of different shapes such as spherically blunted cone, tangent ogive, spherically blunted tangent ogive, secant ogive, elliptical, parabolic, power series, Haack series [19]. For the present turbine, a parabolic nose was considered at first but due to manufacturing difficulties, a hemi-spherical nose was adopted, Fig. 10. The nose was made from a piece of hard wood. The nose is fixed to the head using a threaded short shaft, Fig. 11.
Fig. 10 Turbine nose.
Fig. 11 Fixation of nose to head. 4.2.6 Transmission gear Generally, a transmission gear is used to provide different values of speed and torque. This process is carried out in mechanical engineering by using gears, shafts, belts, pulleys, etc. In the present work, the transmission is simple and consisted of a shaft, two bearings and a pair of gears as shown in Fig. 12. 6
4.2.7 Electricity Generation To generate electricity, the shaft of the turbine must be connected to an electrical generator. Through a transmission gear, the generator converts the mechanical energy of the spinning turbine shaft into electricity. The present wind turbine generates electric power by using a DC generator, which produces DC with 12 V, Fig. 12. It worth mentioning that AC alternator may replace the DC generator. Another option is using DC/AC convertor for wider application.
Fig. 12 Turbine transmission gear and generator inside the casing. 4.2.8 Casing It is used to protect the internal parts of the turbine (generator, gears and shaft). To reduce the cost of production, it was manufactured from a single piece of 8-in (20 cm) commercial plastic pipe, Fig. 13. The casing is installed on the tower by two rips, which in turn are fixed to the tower by two screws. Also, these two screws hold the wooden boom of the wind vane.
(a) Outside.
(b) Inside.
Fig. 13 Turbine casing. 4.2.9 Wind Vane Upwind turbines require a means to keep the rotor on the windward side of the support tower. Wind vane is a tool that is used to direct the turbine in the direction of the blowing wind. 7
The wind vane, Fig. 14, was fabricated from wood for its low cost, light weight, and ease of handling and fixation. The wind vane was installed on a wooden boom with a length of one meter. The casing and the boom of the vane are mounted on a roller bearing to allow movement in all directions. The whole assembly rests on the turbine tower.
Fig. 14 Turbine vane. 4.2.10 Tower and Base The function of the tower is to hold up the turbine in the blowing wind. Tower height is an important factor in the design. The wind blows faster at higher altitudes because of the wind shear near ground surface. Thus, increasing the altitude of the turbine increases the wind speeds. However, the tower height is limited to 2.5 m, Fig. 15. There are some reasons for this height limitation; including: (i) It is expensive to increase the height, (ii) The turbine is suitable for operation on top of tall buildings. Thus, there is no need to increase the tower height. (iii) This height allows the ease of transportation of the turbine for field tests. The tower was made of ductile iron tubes with diameter of 2-in (5 cm). The tower is divided into two pieces to facilitate transportation. Also, a heavy iron base was welded to the lower piece of the tower for holding the turbine without the need for ground fixation.
Fig. 15 Turbine tower and base.
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4.2.11 Battery The function of the battery is to receive the electric energy from wind turbine generator then deliver it to the electric devices. Thus, electric current and voltage become steadier. Moreover, the battery stores the extra energy for consumption when there is not enough wind to operate the turbine. A common 12-V battery, Fig. 16, was used. As the battery is of the type that is used for road vehicles, it is available and cheap.
Fig. 16 12-V Battery. 4.2.12 Electric circuit A simple electric circuit was designed and constructed to test the operation of the present turbine. The circuit, which operates at 12 V, is consisted of battery, fan, lamp (3 Watts), and bell. The circuit is shown in Fig. 17.
Fig. 17 Electric circuit. 4.3 Model assembly After manufacturing and construction of the different components of the turbine, these components are assembled as shown in Fig. 18. The design of the components of the turbine considered the ease of assembling of the turbine.
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Fig. 18 Final assembled turbine. 4.4 Field Tests To validate the operation of the turbine, field tests were carried out in two locations nearby Makkah. These two locations are "El-Hadda Mountain", which is about 40 km from Makkah and "Jaddah Coast", which is about 80 km from Makkah. In the first location, "El-Hadda Mountain", a maximum wind speed of about 12 m/s was recorded at one spot on the mountain. However, at "Jaddah Coast", the maximum recorded wind speed was 9 m/s. 4.4.1 Measuring Instruments (i) Anemometer An anemometer is a device for measuring wind speed, and is a common weather station instrument. The term is derived from the Greek word anemos, meaning wind, and is used to describe any airspeed measurement instrument used in meteorology or aerodynamics. A hand-held anemometer, Fig. 19a, of type EA-3010U [20] was used for the present measurements. It measures maximum, average, and instantaneous wind speeds. Also, it records air temperature. (ii) Tachometer A tachometer is an instrument that measures the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute (rpm) on a calibrated analogue dial or digital screen. Since the rotational speed of the wind turbine is high, there is a need to record its rpm without contact. Thus, a laser tachometer is the 10
proper instrument for this job [21], Fig. 19b. Laser tachometer is a non-contact instrument that is designed for monitoring rotational speeds on a short term. (iii) Multimeter A multimeter is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance. In the present measurements, the multimeter was used to measure the output voltage and current of the wind turbine during operation, Fig. 19c.
(a) Anemometer [20].
(b) Tachometer [21].
(c) Multimeter [22].
Fig. 19 Measuring instruments. 4.4.2 Turbine performance During the field tests a big number of data was recorded at the two test locations. Data covered turbine output power and rotational speed as well as wind speed. Figure 20 shows two samples of the turbine performance curves. These two samples represent the variation of turbine rotational speed (Fig. 20a) and power (Fig. 20b) with the wind speed. In spite of its simple design and ease of manufacturing and assembly, Fig. 20 shows that the turbine operates efficiently for a wide range of wind speed. However, from a practical point of view, it is expected that the turbine will operate in a range of wind speed of 6-8 m/s due to wind conditions in urban and suburban locations. Thus, the expected output power of the turbine will be in the range of 300-400 Watts. This value of turbine power covers the consumption of many electric devices in houses. Perhaps, the only exception is air conditioners that need higher amount of power. For higher output power, more than one turbine can be used in the same site. 4.4.3 Economics When considering the economics of the present wind turbine, certain points should be kept in mind. The total cost of the wind turbine was about 1250 SR (335 USD). It is expected that the price of the turbine may be reduced to one-third of this amount, i.e., about 400 SR (110 USD) for commercial mass production. Even after adding a suitable 11
range of profit, the price of the turbine will be very acceptable and competitive. The turbine life-time is estimated to be 20 years with maintenance cost of only 300 SR (80 USD) during this long period. Thus, it is expected that the turbine will help in reducing the house electricity bill even if it operates for an average of 12 hours per day. Then, it is easy to imagine the big sum of many to be saved when utilizing this turbine for house applications for 20 years.
(a)
(b) Fig. 20 Turbine performance curves.
5. Conclusions Based on the above illustrations and test observations, the following points can be stated: 1- The field tests and measurements proved that the present turbine is efficient. 2- The present turbine is easy to construct and assembly. 3- The price of the present turbine is acceptable and commercially competitive. 4- The turbine is suitable for different sites such as urban, suburban, rural, and sea coast. 5- The output power of the turbine covers the consumption of many electric devices in houses except air conditioners. 6- The turbine has long life-time and needs minimum maintenance.
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7- There is a strong possibility to construct wind farms at the test site of "El-Hadda Mountain" since wind speed exceeded 10 m/s. 6. Recommendations for future work Based on the above discussions, the following recommendations can be listed: 1- Improving the turbine efficiency by using twisted blades. 2- Developing a simple brake system. 3- Developing a control system for turbine orientation. Acknowledgement The authors would like to acknowledge Engs. M. Abo-shagab, M. Al-rehali, S. Algahmdi, S. Al-refai, N. Al-thobaiti, M. Al-zahrani, W. Al-malki, M. Al-otibe, M. Alamodi, A. Al-sharif , Mech. Eng. Dept., Umm Al-Qura Univ., Saudi Arabia, for their efforts in accomplishing this work. Abbreviations AC DC HAWT rpm SR USD V VAWAT
: Alternating current : Direct current : Horizontal-axis wind turbine : Revolution per minute : Saudi riyal : US dollar : Voltage : Vertical-axis wind turbine
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