Folding Mechanism for Micro Wind Turbines
Dhiraj Umaji Devardekar
South Westphalia University of Applied [email protected]
Humans are using a variety of renewable sources of energy for a long time. But, the power generation using these sources is done on a large scale and the devices used for this purpose are huge in size. They are not available for small power generation. Today, the use of portable devices has increased to a large extent and have become an inseparable part of daily life. They work on electricity and must be charged whenever they run out of charging. Considering their daily use, they need charging every now and then as their power source i.e. batteries have low capacity. Wind is an unlimited source of energy and is one of the solutions to this problem. The micro wind turbines (MWTs), are small in size and generates a small amount of energy. This paper works toward making the MWTs portable. These turbines are made convenient to carry using folding mechanisms to charge the devices. The side arms and stand are made compact using a telescopic and tripod stand folding mechanism respectively. The designed turbines generate an electrical output of 11.85 watts when the wind is blowing at a velocity of 5 m/s, which increases with increase in wind velocity. The whole wind turbine converts into three different parts of 0.5 meters length each for transportation and are easy to install. They are capable of charging two small portable devices at a time. This eliminates the need for an unlimited source of power to charge the devices irrespective of the time and place.
Energy is input to drive and improve the life of human beings. The consumption of energy is directly proportional to the progress of humanity in various forms. Nowadays, many people are using portable electronic devices which are accessible and technologically advanced; hence humans have become addicted to them. They all need the energy to run. With our increasing dependency on technology and portable devices, it is impossible to keep charging these devices.
Batteries are the primary power source of these devices; their capacity is one of the limiting factors. They depend on electrical outlets to power them. Most electrical outlets are stationary, which reduce their availability and flexibility while charging. 9
Wind turbines (WTs) are a clean and unlimited source of energy. However, most of the innovations in wind energy have been intended to produce power on a large scale. Those devices are enormous and are not useful in charging portable devices. One step closer to the wind energy leads to the use of micro wind turbines(MWTs) to charge these devices using the unlimited power of the wind. 2
To charge portable devices, these WTs should become portable otherwise it is difficult to carry them. This paper intends to research on a folding mechanism for WTs to make them easy to carry and to provide a clean and unlimited source of power for different portable devices. Chapter three describes the process of selecting the type of turbines, blades and folding mechanisms for the proposed wind turbines. Results and calculations are discussed in the later part of the paper.
The objective of this research is to make use of wind turbines as a never-ending source of energy to charge portable devices. To achieve this goal, folding mechanisms are selected to make it portable to carry and powerful enough to charge the devices.
The first step is to become familiar with different types of wind turbines, blades and then select the best. The primary focus is on the folding mechanism. This research paper considers the existing folding mechanisms, to make the wind turbine portable.
III. Design of wind turbines
A. Types of turbines
Wind turbines are divided into two main types: Horizontal Axis Wind Turbines (HAWTs) and Vertical Axis Wind Turbines (VAWTs). They are used all over the world for high-scale and low-scale power generation.
Table 1: Difference between HAWTs and VAWTs *
1) The axis of rotation is parallel to the direction of wind flow.
1) The axis of rotation is perpendicular to the direction of wind flow.
2) Air strikes from one direction.
2) Air strikes from all directions.
3) Gearbox cannot be placed on the ground.
3) Gearbox can be placed on the ground.
4) The tower is essential; hence the cost of erecting is high.
4) The tower is not essential, hence reducing the cost of erection.
5) A yaw mechanism is required.
5) A yaw mechanism is not required.
6) Control system is required.
6) Control system is not required, hence reducing the cost of frequent maintenance.
“According to the IEC 61400-2 standard of the International Electrotechnical Commission (IEC), WTs are again divided into two classes: small WTs (SWTs), having a rotor-swept area of 200 m2 or less, and large WTs (LWTs), with a rotor-swept area larger than 200 m2. According to the Small and Medium Wind UK Market Report 2013, commercially manufactured SWTs are analyzed in three classes: micro WTs (MWTs), SWTs, and small-medium WTs (SMWTs).” 5
MWTs have less cost of installation compared to other renewable energy resources and are used in places where the electricity is not available. 5
The objective is to generate a small amount of power, and the turbine should be portable enough to carry. Hence the micro VAWT is selected for the desired goal.
B. Selection of the blade type
Depending on the types of blades, there are two primary types of VAWTs: drag-type (Savonius) and lift-type (Darrieus). A drag-type turbine performs better at the initial start-up wind speed and lift-type turbines have higher efficiency.
1) Savonius wind turbines
These blades are used to convert the force of the wind into torque on a rotating shaft. The turbine consists of many airfoils, but not always vertically mounted on a rotating shaft or framework. It is one of the simplest turbines. Aerodynamically, it is a drag type device which consists of two or three scoops, ‘S’ shape in cross-section. These turbines are used whenever cost or reliability is much more important than efficiency.
Figure 1: Savonius Wind Turbines R 7
2) Darrieus wind turbines
This turbine consists of two or three blades mounted on the rotating shaft or framework. This arrangement is equally useful, no matter in which direction wind is blowing. It is a lift type device, and the blades are always symmetrically arranged. Their efficiency is more than that of the Savonius wind turbines.
Figure 2: Darrieus wind turbine 4
The available portable WTs are Savonius WTs. Instead of having high start-up velocity, Darrieus WTs have better efficiency than that of Savonius WTs. Darrieus WT is the one which should be taken into consideration. Hence Darrieus WT is selected.
C. Selection of folding mechanisms
The folding mechanism plays a vital role to make VAWT portable. The folding mechanisms used in existing portable WTs are studied. They are as follows:
1) The Trinity wind turbines
Skajaquoda has designed the Trinity wind turbine. It consists of legs and three blades made up of aluminum and plastic. Trinity uses tripod stand folding mechanism for legs to make it portable. It is basically a Savonius wind turbine.
It holds a 15W generator and a 15,000 mAh battery inside the vertical shaft. It has a weight of about 1.8 kg. The use of tripod stand mechanism helps to reduce the height of Trinity wind turbine to 12″ from a total height of 23″. 2
figure 3: Trinity turbine 1
2) Nils Ferber’s folding WTs for charging smartphones.
Nils Ferber has built this turbine as the project for his Master’s course of product design at the Ecole Cantonale d’art Lausanne (ECAL). It weighs 1 kg. The umbrella folding mechanism is used to make the Savonius blades portable. The turbine installed by pulling on the telescopic shaft based on tension and compression. It is secured with the help of guide ropes.
Figure 4: Nil’s Ferber Folding turbine. (Folding turbine makes smartphone charging in the wild breeze ) 6
“Power output obviously varies depending on wind-speed, but the turbine can reportedly produce a constant output of 5 watts if the wind is blowing at 18 km/h (11 mph).” 6
After observing these available portable WTs, the combination of the folding mechanisms (telescopic mechanism, tripod stand mechanism) is selected.
3) Telescopic folding mechanism
In case of Darrieus VAWT, the blades are mounted on the Vertical shaft with the help of a side arms. To make it portable during transport, reducing the length of side arms is necessary. The telescopic mechanism is used to adjust the length of the arms. Also, it provides us with the flexibility of the cross-section area of the wind turbine.
Figure 5: Telescopic mechanism, (ESTO Connectors) 3
4) Tripod stand mechanism
Selecting a tripod stand mechanism improves the stability of the Micro VAWT. And it is also helpful in accommodating the vertical shaft. Moreover, it simplifies the location of charging outlets. The side arms and blades are made detachable from the vertical shaft to make it convenient to carry.
Figure 6: Tripod stand mechanism, (SIRUI T2204X 4-Section Al (2)) 8
The micro VAWTs with a combination of a telescopic mechanism and a tripod stand mechanism, as discussed above, is shown in figure 7. It consists of three symmetrically arranged Darrieus airfoils. They are mounted on the telescopic side arms, which are flexible in length. The battery and the generator are situated inside the vertical shaft, and the power outlets are provided at the bottom part of the vertical shaft. The vertical shaft is circular in shape, which helps in accommodation of the battery and generator.
The movement of the blades result into rotation of the vertical shaft that generates electricity. The electricity generated is stored in the batteries. Two charging outlets of 5 W capacity and one charging outlet of 10W capacity are placed at the bottom of the vertical shaft. This increases the ease of connecting devices to the turbines for charging.
Figure 7: design of micro VAWT *
A. Power calculations
Power is also an important factor for the designed turbines. They must be powerful enough to charge the devices. The electric power generated by VAWTs is calculated by using the following formula.
= 0.5 ? A Cp
= power (W)
? = air density (kg/ )
A = projected area ( )
V = wind speed (m/s)
Cp= Power Coefficient. 10
The values of air density (1.29) and power coefficient (0.294) at the sea level have been considered for calculations. Now, for designed turbines, if the air is blowing at the speed of 5 m/s, then the power generated by the turbines is 11.85 watts (W).
= 0.5 ? A Cp
= 0.5 x 1.29 x 0.5 x 53 x 0.294
= 11.85 W
This power generated by the turbines is directly proportional to the wind velocity. Hence, it increases with the increase in the wind speed. It gives a power output of 94.815 W and 320W at a wind speed of 10 m/s and 15m/s respectively.
B. Portability of wind turbines
These wind turbines use tripod stand mechanism for legs and telescopic folding mechanism for side arms. The tripod stand brings extra stability to the turbines while installation and the side arms grant great variation in the projected area.
The side arms, blades and vertical shaft are detachable from each other. The length of each part is 0.5 meters, which makes it compact enough to place inside the rucksack or the traveling bags. They are handy to carry when traveling by car as they easily accommodate in the backside of the car.
The aim of this research paper was to design a portable MWTs using folding mechanism. The MWTs are designed by using the tripod stand folding mechanism and telescopic folding mechanism. The turbines have an original height of one meter and convert into the total height of 0.5 meters for transportation. All parts of the turbines are detachable from each other. Hence, the total setup changes into three parts with 0.5-meters length.
These turbines produce a power output of 11.85 W at a wind speed of 5 m/s. This power is enough to charge two small portable devices or one high power device at a time. This eliminates the requirement of continues power source.
These turbines are useful when we travel to remote locations where the electrical outlets are not available and are capable of charging our devices anytime. They are also useful when used at locations such as highways where the artificial air velocity created due to movement of vehicles on both sides of the turbines is capitalized to rotate the turbines and generate the electricity to lighten up the highways as well as to run the sign-boards.
1 Darek, M., “Trinity – The Portable Wind Turbine Power Station.” Available: https://www.kickstarter.com/projects/skajaquoda/trinity-the-portable-wind-turbine-power-station (accessed November 20, 2017).
2 Darek Markham, “This tiny portable wind turbines fit in your bag and charges your gadgets.” treehugger, 2014.
3 ESTO Connectors: 1″ to 3/4″ Telescoping Assembly. Available: http://www.estoconnectors.com/product/pn-telescoping-assembly-pictures (accessed November 24, 2017).
4 File:Darrieus.jpg – Wikimedia Commons, 2017. Available: https://commons.wikimedia.org/wiki/File:Darrieus.jpg (accessed November 24, 2017).
5 Hayati MAMUR, “Design, application, and power performance analyses of a micro wind turbine,”
6 Robarts, S., “Folding turbine makes smartphone charging in the wild a breeze.” Available: https://newatlas.com/nils-ferber-micro-wind-turbine/44879/#p418667 (accessed November 9, 2017).
7Vertical-Axis Wind Turbine (VAWT) Project Available: http://jase4yaz.weebly.com/ (accessed January 23, 2018).
8 SIRUI T2204X 4-Section Aluminum Camera Tripod Stand. Available: https://www.zapalslot.com/sirui-t2204x-carbon-fiber-camera-tripod-stand-4-section-for-slr.html (accessed November 24, 2017).
9 “Why you need portable energy!”, WindSoleil, 2015. Available: https://www.windsoleil.com/blog/2015/2/14/why-you-need-portable-power
10 Himanshu Naik, RM Holmukhe, Sailor Jignesh, Irawati Naik, “Small scale vertical axis wind power generation a practical study with social perspective for rural India”.
* Own illustrations.
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