Overview of Vertical Axis Wind Turbine (VAWT) is one of the Wind Energy Application

Abstract

This paper reviews the available types of wind turbine which is one of the wind energy applications. The authors intend to give investors a better idea of which turbine is suitable for a particular setting and to provide a new outlook on vertical axis wind turbines. Wind technology has grown substantially since its original use as a method to grind grains and will only continue to grow. Vertical-axis wind turbines are more compact and suitable for residential and commercial areas while horizontal-axis wind turbines are more suitable for wind farms in rural areas or offshore. However, technological advances in vertical axis wind turbines that are able to generate more energy with a smaller footprint are now challenging the traditional use of horizontal wind turbines in wind farms. Vertical axis wind turbines do not need to be oriented to the wind direction and offer direct rotary output to a ground-level load, making them particularly suitable for water pumping, heating, purification and aeration, as well as stand-alone electricity generation. The use of high efficiency Darrieus turbines for such applications is virtually prohibited by their inherent inability to self-start.

Full text

Overview of Vertical Axis Wind Turbine (VAWT) is one of the Wind
Energy Application
Farhan Ahmed Khammas1,a Kadhim Hussein Suffer2,b,
Ryspek Usubamatov3,c, Mohammad Taufiq Mustaffa 4,d
1,2,3.4 School of Manufacturing Engineering, University Malaysia Perlis, Arau, Perlis, Malaysia.
afar_1961ah@yahoo.com, bkadhim_askar@yahoo.com, cryspek@unimap.edu.my,
dmohammadtaufiq@unimap.edu.my
Keywords: Wind Energy, Vertical Axis Wind Turbine, Darrieus turbine, Savonius turbine.
Abstract. This paper reviews the available types of wind turbine which is one of the wind energy
applications. The authors intend to give investors a better idea of which turbine is suitable for a
particular setting and to provide a new outlook on vertical axis wind turbines. Wind technology has
grown substantially since its original use as a method to grind grains and will only continue to
grow. Vertical-axis wind turbines are more compact and suitable for residential and commercial
areas while horizontal-axis wind turbines are more suitable for wind farms in rural areas or
offshore. However, technological advances in vertical axis wind turbines that are able to generate
more energy with a smaller footprint are now challenging the traditional use of horizontal wind
turbines in wind farms. Vertical axis wind turbines do not need to be oriented to the wind direction
and offer direct rotary output to a ground-level load, making them particularly suitable for water
pumping, heating, purification and aeration, as well as stand-alone electricity generation. The use of
high efficiency Darrieus turbines for such applications is virtually prohibited by their inherent
inability to self-start.
Introduction
The difficulty and expense of getting fuel to remote areas of the country to use as a source of
energy and the threat of expanding pollution of air have forced many countries to switch to
alternative energy sources, to meet their needs. It is only now after twenty years of cheap fuel, that
the true cost of energy is really being felt. By far our biggest source of primary energy has been
fossil fuels burned in homes, factories and in power stations to produce heat and electricity. Not
only have hydrocarbons provided us with power, they have also given us liquid fuel for transport
and have been used to produce the many types of plastics we use in our daily life.
Energy has been and will still be the main stay of any economy. There are many different types
of energy. Potential energy is the energy available because of the position between particles for
example, water stored in a dam, the energy in a coiled spring, and energy stored in molecules
(gasoline). Kinetic energy is energy available in the motion of particles wind energy is one example
of this. There are many examples of energy: mechanical, electrical, thermal, chemical, magnetic,
nuclear, biological, tidal, geothermal, and so on. A renewable energy revolution is our hope for a
sustainable future. Clearly, the future belongs to clean energy sources and to those who prepare for
it now.
Solar and wind energy often provide least-cost options for economic and community
development in rural regions around the globe, while supplying electricity, creating local jobs, and
promoting economic development with clean energy resources. The future will be a mix of energy
technologies with renewable sources such as solar, wind, and biomass playing an increasingly
important role in the new global energy economy.
Applied Mechanics and Materials Vol. 793 (2015) pp 388-392 Submitted: 2015-02-25
© (2015) Trans Tech Publications, Switzerland Accepted: 2015-06-17
doi:10.4028/www.scientific.net/AMM.793.388
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans
Tech Publications, www.ttp.net. (ID: 58.27.57.123-11/07/15,17:37:49)

The developments of renewable energy especially wind energy become widely since 1973 due to
the oil crisis issues. Wind energy is the conversion of wind kinetic energy into a useful form, such
as mechanical or electrical energy that can be harnessed for practical use by using wind turbines.
Wind turbines have come a long way since their original use in mechanical applications.
Wind turbine is a machine for converting the kinetic energy available in the wind into
mechanical energy. When wind’s mechanical energy is used directly by machinery to pump water
or to grind stones, this machine called a windmill [1].The earliest windmills were invented in
Sistan, Iran in 7th century [2].They were used to grind corn and pump water as shown in Fig. 1 (a).
During the middle ages, the first windmill built in Europe is the Dutch Windmill for same tasksas as
shown in Fig. 1 (b) [3]. The first attempt to convert wind’s mechanical energy to electricity by a
horizontal wind turbine was built in Scotland in 1887 and a larger one was built in Cleveland, Ohio
in 1888 by Charles Brush, as shown in Fig. 1 (c) [4].
In the wind power domain two main technologies were considered as having the necessary
potential for available development: the Horizontal Axis Wind Turbine (HAWT) as shown in Fig. 1
(b, c) and the Darrieus-type (lift-based) Vertical Axis Wind Turbine (VAWT) as shown in Fig. 2
(b).
Figure 1. (a) Persian windmill, (b) Charles Brush wind turbine, Cleveland, Ohio, (c) Charles
Brush wind turbine, Cleveland, Ohio [4].
The main advantages of HAWTs are the blades to the side of the turbines center of gravity, helping
stability, ability to wing warp, which gives the turbine blades the best angle of attack, allowing the
angle of attack to be remotely adjusted gives grater control, so the turbine collect the maximum
amount of wind energy for the time of day and session, ability to bitch the rotor blades in a strong,
to minimize damage, tall tower allows access to stronger wind in sites with wind shear. The
disadvantages of a horizontal axis wind turbine it has difficulty operating in near ground, turbulent
winds because their yaw and blade bearing need smoother, more laminar wind flows, the tall towers
and long blades (up to 40 m long) are difficult to transport on the sea and on land, transportation can
now cost 20% of equipment costs, tall HAWTs are difficult to install, needing very tall and
expensive cranes and skilled operators. VAWTs have many advantages like; easier to maintain,
airfoils or rotor blades are connected by arms to a shaft that sits on a bearing and drives a generator
below, usually by first connecting to a gearbox, the rotor blades are vertical, a yaw device is not
needed, reducing the need for this bearing and its cost, VAWTs have a higher drag at low and high
pressures, it can be placed close to the ground and produce more power than HAWTs placed higher
up. It is accepted that vertical axis wind machines represent a suitable alternative for wind power
extraction in many developing countries. The reason for this is mainly because of the advantage
over the horizontal axis type such as simple construction, extremely cost effective and acceptance
Applied Mechanics and Materials Vol. 793 389

of wind flow from any direction without orientation. In spite of these advantages VAWTs is not
gaining popularity because of low efficiency of the Savonius type rotor and low starting torque of
the Darrieus type wind machines.
Propeller type wind turbines
Modern propeller type wind turbines use the wind lift force as an aircraft wing due to the shape and
geometry of the blades, and are neither built with many rotor blades nor with very wide blades. The
number of the blades of a turbine has great impact on its performance. Large number of rotor blades
decreases the stability of the turbine. Propeller type wind turbines built on the tower and cannot use
guy wires to support one, because the propeller spins both above and below the top of the tower.
These turbines require a strong tower that grows dramatically with the size of the propeller. Other
disadvantage of the propeller type wind turbine is most of the wind passing through the space
between blades and misses them completely and so this wind kinetic energy does not use by blades.
Actual efficiency of the propeller type turbines is 20% [5].
Savonius wind turbine
The Savonius wind turbine was invented by the Sigurd Johannes Savonius in 1922 as shown in Fig.
3 (a). However, these turbines are one of the simplest self-starting VAWTs. Aerodynamically, they are
drag-type devices, consisting of two or three scoops. The differential drag causes the Savonius turbine
to spin. Some designs have long helical scoops, to give smooth torque. Much of the swept area of a
Savonius rotor is near the ground, making the overall energy extraction less effective due to lower wind
speed at lower heights. According to Savonius, the best of his rotor had a maximum efficiency of 31%
while the maximum efficiency of the prototype was 37%. Following Savonius, Newman, Sivasegaram
and Khan, they were conducted several experiments to investigate the effect of geometrical parameters
such as blade gap size, overlap etc. [6]. The most ubiquitous application of the Savonius wind turbine is
the ventilator which is commonly seen on the roofs of vans and buses and is used as a cooling device.
Figure 2. Vertical axis wind turbine (a) Savonius (drag base), (b) Darrieus in Magdalen Islands
and (c) Giromill (lift based). [4].
Darrieus wind turbine
The first attempt to generate electricity were made at the end of 19th century, and they become
more and more frequent in the first half of the following century. The Darrieus type machine was
invented and patented in 1925 by G.J. Darrieus, a French Engineer the most famous and common
type of VAWT that still bears his name as shown in Fig. 2 (b). Darrieus wind turbine is a type of
VAWTs used to generate electricity from the energy carried in the wind. Darrieus wind turbines can
rotate with high speed with low torque and can be useful for small pumps and small electrical
generators. Efficiency of the Darrieus type turbines is less than 10% [7]. Some design of the blades
390 Electrical Power Engineering and Sustainable Development of Industry

canted into a helix that spreads the torque evenly over the entire revolution, thus preventing
destructive pulsations. Modifications of the Darrieus turbine are the Giromill and Cycloturbines Fig.
2 (c). The main advantage to these designs are that the torque generated remains almost constant
over a fairly wide angle, have the advantage of being able to self-start, by pitching the "downwind
moving" blade flat to the wind to generate drag and start the turbine spinning at a low speed. On the
downside, the blade pitching mechanism is complex and generally heavy, and the wind-direction
sensor needs to be added in order to pitch the blades properly. Combining the rotor is generally one
of the many ways to optimize and overcome the problem of low starting torque on Darrieus wind
turbine. Although the savonius rotor has a low power cofficient than Darrieus rotor, its useful
characteristic is its high starting torque and selfstarting at low tip speed ratio.It works by producing
a large starting torque from the Savoniuse rotor but at higher tip speed ratio operated by Darrieus
rotor [8].
Vane type Vertical Axis Wind Turbine (VVAWT).
The technical characteristics of known designs of wind turbines show that there is a necessity to
design a new type of wind turbines which allows wind force to be harnessed to the maximum, and
with the ability to be used in wide areas of application. The new design should use wind kinetic
energy to the maximum of the Betz limit [9]. The active area of blades, vanes or other elements of
the new wind turbines should give less geometrical sizes. The problem can be solved by a new
design of a vertical axis vane type wind turbine like VVAWT as shown in Fig.3 [11]. This type of
turbine has a simple construction, a technologically simple production method, and uses drag force
by the active area of the working elements.
Figure 3. (a) Sketch of the flat blade vane type wind turbine, (b) and general view of wind
station, (c) Sketch of the cavity vane type, and (d) Top view of three and four frames.
The VVAWT is a special design consists of movable vanes that create scoop shape when closed.
Scoop shape of these frame increases the drag factor and increase the torque. The VVAWT can be
designed in two types first the three frames with angles of 120° between one, in the other side of
impeller movable vanes are opened under action of wind and the air pass freely to reduce the
negative torque, the second is four frames with angles of 90° between one and horizontally
constructed bars with vanes that have ability to twist on 90° as shown in Fig.3 (d). This design
enables the wind force to close left side vanes and simultaneously opens the right side vanes.
Vertical frames should be connected by bars to increase the construction stiffness (did not showed
on the sketch). Other components of the wind turbine like the tower can be made from metallic
frame and so forth and designed according to the area of application of the wind station [10].
Applied Mechanics and Materials Vol. 793 391

Conclusions
Wind power is the most popular sources of alternative energy because it is a clean, emissions-free
power generation technology and it is based on capturing the energy from natural forces and has
none of the polluting effects associated with fossil fuels. Wind turbine is a machine for converting
the kinetic energy available in the wind into mechanical energy. Modern wind turbines are divided
into two main types based on their rotational axis: the HAWTs and the VAWTs. The efficiency of
the VAWTs highly depends on the aerodynamics of the blades.
The propeller type wind turbine with blades has higher efficiency compared with flat vanes. This
is caused the wind turbine has the high drag factor enables to capture wind energy. This type wind
turbine has good technical properties and can be used for generating a power more efficiently for
the low speed of the wind. The new turbine presents simple construction and for manufacturing can
use simple technology and produce from cheap materials [10, 13]. Combining the rotor is generally
one of the many ways to optimize and overcome the problem of low starting torque on Darrieus
wind turbine.
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