Wind energy in the upwind
By:Vasilescu Tiberiu Aurel
And Brata Sorin
1. Short presentation
2. History of wind energy
3. Wind Turbines: Upwind Machines
4. How wind machines work
5. Types of wind turbines
5.1. Vertical-axis wind turbines
5.1.2.Advantages and disadvantages
5.2. Horizontal-axis wind turbines
5.2.2.Advantages and disadvantages
6. Small wind turbines
7. Turbine design and construction
8. The benefits of wind energy
9. Wind and the environment
10. The costs of wind energy
Wind is simple air in motion. It is caused by the uneven
heating of the earth’s surface by the sun.
Wind energy converts kinetic energy that is present in the
wind into more useful forms of energy such as
mechanical energy or electricity.
During the day, the air above the land heats up more
quickly than the air over water. The warm air over the
land expands and rises, and the heavier, cooler air rushes
in to take its place, creating winds. At night, the winds
are reversed because the air cools more rapidly over land
than over water.
In the same way, the large atmospheric winds that circle
the earth are created because the land near the earth's
equator is heated more by the sun than the land near the
North and South Poles.
Today, wind energy is mainly used to generate electricity.
Wind is called a renewable energy source because the
wind will blow as long as the sun shines.
Windmills that were used to grind grain are an example
of early uses of wind energy. Modern uses of wind
energy include generation of electricity and pumping
water. Current wind energy machines are called "wind
turbine generators", "wind pumps", or more generally,
History of wind and wind energy
Since ancient times, people have harnessed the winds
energy. Over 5,000 years ago, the ancient Egyptians used
wind to sail ships on the Nile River. Later, people built
windmills to grind wheat and other grains. The earliest
known windmills were in Persia (Iran). These early
windmills looked like large paddle wheels. Centuries later,
the people of Holland improved the basic design of the
American colonists used windmills to grind wheat and
corn, to pump water, and to cut wood at sawmills. As late
as the 1920s, Americans used small windmills to generate
electricity in rural areas without electric service.
The oil shortages of the 1970s changed the energy picture
for the country and the world. It created an interest in
alternative energy sources, paving the way for the re-entry
of the windmill to generate electricity. In the early 1980s
wind energy really took off in California, partly because
of state policies that encouraged renewable energy
Humans have used wind energy for thousands of years.
Ancient Persians used wind energy to pump water before
the birth of Christ.
The current interest in wind energy was started by the
need to develop clean, sustainable energy systems that
can be relied on for the long-term future.
Wind Turbines: Upwind Machines
Upwind machines have the rotor facing the
wind. The basic advantage of upwind
designs is that one avoids the wind shade
behind the tower. By far the vast majority of
wind turbines have this design.
On the other hand, there is also some wind
shade in front of the tower, i.e. the wind
starts bending away from the tower before it
reaches the tower itself, even if the tower is
round and smooth. Therefore, each time the
rotor passes the tower, the power from the
wind turbine drops slightly.
The basic drawback of upwind designs is
that the rotor needs to be made rather
inflexible, and placed at some distance from
the tower (as some manufacturers have
found out to their cost). In addition an
upwind machine needs a yaw mechanism to
keep the rotor facing the wind.
How wind machines work
Like old fashioned windmills, today’s wind
machines use blades to collect the wind’s kinetic
energy. Windmills work because they slow down
the speed of the wind. The wind flows over the
airfoil shaped blades causing lift, like the effect on
airplane wings, causing them to turn. The blades
are connected to a drive shaft that turns an
electric generator to produce electricity.
With the new wind machines, there is still the
problem of what to do when the wind isn’t
blowing. At those times, other types of power
plants must be used to make electricity.
Types of wind turbines
There are two types of wind machines (turbines) used today based on the direction of
the rotating shaft (axis): horizontal–axis wind machines and vertical-axis wind
machines. The size of wind machines varies widely. Small turbines used to power a
single home or business may have a capacity of less than 100 kilowatts. Some large
commercial sized turbines may have a capacity of 5 million watts, or 5 megawatts.
Larger turbines are often grouped together into wind farms that provide power to the
Vertical-axis wind turbines (or VAWTs)
have the main rotor shaft running vertically.
Key advantages of this arrangement are that
the generator and/or gearbox can be placed
at the bottom, near the ground, so the tower
doesn't need to support it, and that the
turbine doesn't need to be pointed into the
wind. Drawbacks are usually pulsating
torque that can be produced during each
revolution and drag created when the blade Savonius wind turbine
rotates into the wind. It is also difficult to
mount vertical-axis turbines on towers,
meaning they must operate in the often
slower, more turbulent air flow near the
ground, resulting in lower energy extraction
Exemples of vertical-axis wind turbines:
Darrieus wind turbine
Savonius wind turbine Darrieus wind
Vertical-axis wind turbines
Advantages: Disadvantages :
Easier to maintain because most of their moving parts Most VAWTs produce energy at only 50%
are located near the ground. This is due to the vertical of the efficiency of HAWTs in large part
wind turbine’s shape. The airfoils or rotor blades are because of the additional drag that they
connected by arms to a shaft that sits on a bearing and have as their blades rotate into the wind.
drives a generator below, usually by first connecting to This can be overcome by using structures
a gearbox. to funnel more and align the wind into the
rotor or the "vortex" effect of placing
As the rotor blades are vertical, a yaw device is not straight bladed VAWTs closely together
needed, reducing the need for this bearing and its cost.
There may be a height limitation to how
Vertical wind turbines have a higher airfoil pitch angle, tall a vertical wind turbine can be built and
giving improved aerodynamics while decreasing drag at how much sweep area it can have.
low and high pressures. However , this can be overcome by
Low height useful where laws do not permit structures connecting a multiple number of turbines
to be placed high. together in a triangular pattern with
Smaller VAWTs can be much easier to transport and bracing across the top of the structure .
install. Thus reducing the need for such strong
Does not need a free standing tower so is much less vertical support , and allowing the turbine
expensive and stronger in high winds that are close to blades to be made much longer .
the ground. Most VAWTS need to be installed on a
Does not need to be pointed into the wind, can turn relatively flat piece of land and some sites
regardless of the direction of the wind. could be too steep for them but are still
usable by HAWTs.
They can potentially be built to a far larger size than
HAWT's , for instance floating VAWT's hundreds of Most VAWTs have low starting torque,
meters in diameter where the entire vessel rotates , can and may require energy to start the
eliminate the need for a large and expensive bearing . turning.
Horizontal-axis wind turbines have the main rotor shaft and
electrical generator at the top of a tower, and must be pointed
into the wind. Small turbines are pointed by a simple wind
vane, while large turbines generally use a wind sensor coupled
with a servo motor. Most have a gearbox, which turns the slow
rotation of the blades into a quicker rotation that is more
suitable to drive a generator.
Since a tower produces turbulence behind it, the turbine is
usually pointed upwind of the tower. Turbine blades are made
stiff to prevent the blades from being pushed into the tower by
high winds. Additionally, the blades are placed a considerable
distance in front of the tower and are sometimes tilted up a
Downwind machines have been built, despite the problem of
turbulence, because they don't need an additional mechanism
for keeping them in line with the wind, and because in high
winds, the blades can be allowed to bend which reduces their
swept area and thus their wind resistance. Since turbulence
leads to fatigue failures, and reliability is so important, most
HAWTs are upwind machines.
Types of Horizontal-axis wind trubines:
Modern Rural Windmills
Common modern wind turbines
Horizontal-axis wind turbines
Blades are to the side of the turbine's HAWTs have difficulty operating in
center of gravity, helping stability. near ground, turbulent winds.
Tall tower allows access to stronger wind The tall towers and long blades (up to
in sites with wind shear. In some wind 180 feet (55 m) long) are difficult to
shear sites, every ten meters up, the wind transport on the sea and on land.
speed can increase by 20% and the power Transportation can now cost 20% of
output by 34%. equipment costs.
Tall tower allows placement on uneven Supply of HAWTs is less than demand
land or in offshore locations. and between 2004 and 2006, turbine
Can be sited in forests above the tree line. prices increased up to 60%. At the end
Most are self-starting. of 2006, all major manufacturers were
booked up with orders through 2008.
Can be cheaper per unit of output because The FAA has raised concerns about tall
of higher production volume, larger sizes HAWTs effects on radar near Air Force
and, in general, higher capacity factors bases.
Their height can create local opposition
based on impacts to viewsheds.
Small wind turbines
Small wind turbines may be as small as
a four hundred watt generators for
residential use. The small ones often
have direct drive generators, direct
current output, aeroelastic blades,
lifetime bearings and use a vane to
point into the wind. Larger, more
costly turbines generally have geared
power trains, alternating current
output, flaps and are actively pointed
into the wind. Direct drive generators
and aeroelastic blades for large wind
turbines are being researched.
A small wind turbine can be installed
on a roof. Installation issues then
include the strength of the roof,
vibration, and the turbulence caused by
the roof ledge.
Turbine design and construction
Wind turbines are designed to exploit the wind
energy that exists at a location. Aerodynamic
modeling is used to determine the optimum tower
height, control systems, number of blades, and
Virtually all modern wind turbines convert wind
energy to electricity for energy distribution. As
described, the modern wind turbine is a system
that comprises three integral components with
distinct disciplines of engineering science. The
rotor component, which is approximately 20% of
the wind turbine cost, includes the blades for
converting wind energy to an intermediate low
speed rotational energy. The generator
component, which is approximately 34% of the
wind turbine cost, includes the electrical
generator, the control electronics, and most likely
a gearbox component for converting the low
speed rotational energy to electricity. The
structural support component, which is
approximately 15% of the wind turbine cost,
includes the tower for optimally situating the rotor
component to the wind energy source.
The benefits of wind energy
Wind energy is an ideal renewable energy because:
It is a pollution-free, infinitely sustainable form of energy
It doesn’t require fuel
It doesn’t create greenhouse gasses
It doesn’t produce toxic or radioactive waste.
Wind energy is quiet and does not present any significant hazard to birds or
When large arrays of wind turbines are installed on farmland, only about 2% of
the land area is required for the wind turbines. The rest is available for farming,
livestock, and other uses.
Landowners often receive payment for the use of their land, which enhances
their income and increases the value of the land.
Ownership of wind turbine generators by individuals and the community
allows people to participate directly in the preservation of our environment.
Each megawatt-hour of electricity that is generated by wind energy helps to
reduce the 0.8 to 0.9 tonnes of greenhouse gas emissions that are produced by
coal or diesel fuel generation each year.
Wind and the environment
In the 1970s, oil shortages pushed the
development of alternative energy sources.
In the 1990s, the push came from a
renewed concern for the environment in
response to scientific studies indicating
potential changes to the global climate if
the use of fossil fuels continues to increase.
Wind energy is an economical power
resource in many areas of the country.
Wind is a clean fuel; wind farms produce
no air or water pollution because no fuel is
burned. Growing concern about emissions
from fossil fuel generation, increased
government support, and higher costs for
fossil fuels have helped wind power
capacity in the United States grow
substantially over the last 10 years.
The most serious environmental drawbacks
to wind machines may be their negative
effect on wild bird populations and the
visual impact on the landscape.
The costs of wind energy
The cost of wind energy is determined by:
The initial cost of the wind turbine installation
The interest rate on the money invested
The amount of energy produced
Any wind turbine that is installed in a very windy
area generates less expensive electricity than the
same unit installed in a less windy area. So it’s
important to assess the wind at the potential site.
Modern wind turbine generators cost between $1500
and $2000 per kilowatt for wind farms that use
multiple-unit arrays of large machines. Smaller
individual units cost up to $3000 per kilowatt. In
good wind areas, the costs of generating electricity
range between five and ten cents per kilowatt hour.
That cost is somewhat higher than the costs
associated with an electrical facility, but wind energy
costs are decreasing every year, whereas most
conventional generation costs continue to increase.