This document provides an overview of wind turbines and their mechanical properties. It discusses how wind turbines work by capturing the kinetic energy of wind and converting it to electrical energy. The key components that enable this are the turbine blades, which are designed with an aerodynamic shape called an aerofoil that generates lift from the wind. The optimal angle of attack for the blades is important to maximize energy capture while avoiding stall. Wind turbines start generating power at a minimum wind speed and reach maximum power output at their rated wind speed before feathering their blades at very high wind speeds to protect components. The theoretical maximum efficiency of a wind turbine is calculated as 1/3 of the incoming wind speed based on fluid dynamics principles.

1. 1
Independent Study: The Mechanical Properties of Wind Turbines
Table of Contents
1. Introduction ......................................................................................................................... 2
1.1 Need for new energy...................................................................................................2
1.2 What is a wind turbine?............................................................................................... 2
1.3 Aims and objectives ....................................................................................................2
2 Main Part............................................................................................................................. 3
2.1 Principles..................................................................................................................... 3
2.1.1 Kinetic energy ......................................................................................................3
2.1.2 Aerofoil ................................................................................................................. 3
2.2 Generating Electricity..................................................................................................5
2.3 The Power Efficiency of a HAWT ............................................................................... 7
2.4 Wind turbine design ....................................................................................................9
2.4.1 Hub and Tower design......................................................................................... 9
2.4.2 Designing the blades ........................................................................................... 9
2.4.3 Wind turbine overall expenses .......................................................................... 12
2.5 Study case: Den Brook wind farm ............................................................................ 12
3 Discussion......................................................................................................................... 14
3.1 How to enhance wind turbine designs?.................................................................... 14
3.2 Are these technological improvements worthwhile? ................................................ 15
4 Conclusion........................................................................................................................ 17
5 References........................................................................................................................ 18

2. 2
1. Introduction
1.1 Need for new energy
All over the world people are looking to improve their standard of living and the global
population is expanding rapidly. The combination of the two results in an increasing
consumption of food and energy. The only way to satisfy these growing needs on such a vast
scale is to find a more sustainable way of producing them by lowering waste and Greenhouse
gases such as CO2 that damage the ozone layer.
The sun continuously supplies the earth with more energy in day than the entire population,
of 7 billion people, consumes in a year! This energy is unlimited and has the potential to
provide this growing world with all its energy need. Unlike popular belief, it is not limited to
capturing rays from the sun, but also its spinoffs such as low geothermal, wind based and
even hydroelectric energy (Conserve-Energy-Futur, 2016).
1.2 What is a wind turbine?
- Ask me what I think of Wind Turbines? - Big Fan!
The first ever windmill for electricity production was
founded in Scotland in 1887 and muchhas changed since.
Although designs stayed vary basic until the 1960s, it
wasn’t until the oil crisis in 1973 that the development of
many fossil fuel alternatives made technological
advantages. Throughout the 70s NASA kick started an
innovative research into large commercial wind turbines
for multi-megawatt technologies. (Nixon, 2008). During
this period many novel ideas for oil substitutes were finally
given the opportunity to be tested and wind turbines were
one of them.
A wind turbine is a device that converts wind power into
electricity. There are many different designs, vertical or horizontal axis, different sizes such as
those used for domestic or commercial purposes and lastly they can be onshore or offshore.
This report targets the properties of the mostfrequently used design of all, the onshore HAWTs
(Horizontal Axis Wind Turbine) used mainly for commercial purposes. In particular, it
investigates how to promote their development a potential renewable substitute to current
fossil fuel based energies that will eventually run out.
1.3 Aims and objectives
The aim of this project is to find out how wind turbine generate electricity from the wind and
whether they are a suitable solution for generating power in the future.
This project investigates the aerodynamic concepts behind wind turbine designs along with
choices of materials used to make them most efficient.
A casestudy from the South Westof England is also included to assess awind turbines impact
and contributions to local communities.This will prove a good way to compareif any prejudices
and expectations were true.

3. 3
2 Main Part
2.1 Principles
How do you extract energy from wind?
2.1.1 Kinetic energy
HAWTs use their blades, to capture energy from flowing wind, and turn it into electrical energy
which is then supplied to the main service grid.
Wind flow is created from different high and low pressure pockets of air formed by the heat of
the sun. This is because when the sun rises, it warms up the air molecules and causes them
to rise and dilate. Therefore, a pressure drop is left behind for cold air molecules to take its
place. This produces a flowing movement of air and when it happens fast enough over a large
scale, this phenomenon is called wind. So technically speaking, wind energy is just another
way of using energy from the sun which is unlimited and 100% renewable.
Since wind is moving air, it is also a moving fluid with a mass and velocity, therefore possess
a form of energy called momentum. So, it generates kinetic energy given by:
𝐾. 𝐸 = 0.5 × 𝑚 × 𝑉𝑤𝑖𝑛𝑑
2
Using Newton’s 2nd
law,
𝐹 = 𝑚. 𝑎 = 𝑚
𝑑𝑣
𝑑𝑡
the flow generates a force which is partially lost by the wind when the moving fluid it meets
the turbine’s blades. The same force that is lost by the wind is actually transferred at this point
into a reaction force. The redirection of this reaction into lift, comes from the shape of the
blades’ cross section and causes the blades to rotate. The turbine absorbs energy from the
wind flowing through the circular surface area covered by its rotating blades.
2.1.2 Aerofoil
The key part of a HAWT’s design is the aerodynamic shape of the blade used which produces
a lift force called an aerofoil. These turbines are designed to be lift based, this is because their
blade shape generates a lift force in the normal direction to the incoming wind passing over
the blade’s surface, causing them to rotate.
Bernoulli’s principle simply states the conservation of energy for a fluid, this relation is given
is Figure 1. An aerofoil is made up of a curved upper surface and a flatter lower surface, as
shown in Figure 2. Since the incoming wind cannot pass through the aerofoil, it must separate
and travel along both surfaces. Furthermore, the angle between the incoming wind and the
chord line, the line between the leading and trailing edge, has a major impact on the way the
air flows. The air travels faster over the curved surface than the flatter surface. Then by
Bernoulli’s principle as the wind’s velocity increases, its pressure drops. Therefore, there is a
low pressure region above the curved surface, whereas on the lower surface the pressure
remains similar to or slightly higher than the pressure in the free stream. Hence, the
combination of low pressure, on the curved side of the blades and higher pressure around the
opposite side creates a negative pressure difference (Pcurv e-Pf lat<0). Thus, the blade is pulled
in the direction of the curved surface which causes the turbine to rotate. (Ltd, 2016)

4. 4
Figure 1: Bernoulli's Principle: Energy Conservation Equation for a Fluid
Figure 2: Cross section view of a curved blade: Aerofoil
A blade always moves in a perpendicular direction to the incoming wind. Therefore, it has a
relative velocity to the wind. Using a vector field this can be described as Vrel = Vwind - Vblade.
The relative velocity has two components:the actual velocity of the wind (Vwind) and the velocity
of the blade (Vblade). The aerofoil means that the force from Vwind is perpendicular to Vwind and
the same direction as Vblade (Learn Engineering, 2014). This concept is illustrated in Figure 3
below.
Figure 3: Illustration of the relative velocity concept (source: learnengineering.org, Working and design details of
Wind Turbines, 2013 )
The angle of attack (AOA) is the angle of relative wind and the chord line of the aerofoil. As
mentioned previously, it mustbe precisely set up in order to take full advantage of the aerofoil.
Which means that blades are pitched to point into the direction of the optimal relative velocity
of the wind rather than the actual wind direction.
The greater the angle the more desired lift force is produced. However, after a certain point
stalling will occur and cause the blade to stop rotating. Therefore, as shown in Figure 4, there
is an optimum angle of attack which generates the most lift and provides the turbine with the
most power.

5. 5
Figure 4: Illustrations ofLow,Medium and High AOA (source:Gurit, Wind Turbine Blade Aerodynamics (Handbook
2))
Additionally, the speed of the turbine blade increases from hub to tip. This effect is described
using the ‘Tip-Speed-Ratio’ (TSR):
𝑻𝑹𝑺 =
𝝎𝑹
𝑽
. where ω is the angular velocity of the rotor, R is the distance between the centre
of the hub and the tip of the blade, and V is the wind speed.
To compensate for this, a continuous twist is given to the blade to ensure that the aerofoil
keeps the same angle of attack throughout its length.
As the AOA increases so does the drag force, particularly after stalling. If the aerofoil shape
is well designed, the lift outweighs the drag significantly translating in a high lift to drag ratio.
Therefore, the blade reaches its maximum lift to drag ratio just before the maximum lift angle.
As shown in Figure 5, the lift coefficient is greatest at the curves turning point. Nonetheless,
beyond this point stalling will occur and the HAWT would stop spinning. Therefore, engineers
attempt to get as close to this point as safely possible.
Figure 5: Graphs illustrating the critical AOA for Lift and drag coefficients (Pilotsweb.com, 2005)
Obviously, incoming wind direction can vary which makes the blade pitch control important, in
order to keep the blade angle as efficient as possible, as well as maintaining the turbine within
a safe operating range as discussed previously.
2.2 Generating Electricity
In the UK, annual wind speeds average around 6 m/s, which alone is currently too low to
capture enough momentum in order generate any significant power.
Therefore, the spinning shaft is connected to a gear box which converts low rotation speeds
into higher rotation speeds to a shaft on the other end connected to an electricity generator in
the nacelle. A gear box usually increases the angular speed of the rotor shaft from 15-30
rotations per minute (rpm), to about 1,000-1,800 rpm; which is the rotational speed needed by
most generators to produce electricity. For large wind turbines, which produce more than 2
MW, the voltage generated is usually 690 V in alternating current (AC). This current is
transmitted through a cable down the tower into a step up transformer to raise the voltage to
10,000 - 30,000 volts, depending on the standard in the local electrical grid. This step up
transformeris typically at the base of the tower and is used to boost the output of the electricity

6. 6
generator. The higher voltage is then linked up to a collector which is connected to several
wind turbines before flowing into the grid (U.S. Department of Energy, 2016).
However, wind turbine generators are very specific because they must run on fluctuating
torque from the blades which vary with ever changing wind speed. Obviously, the more wind,
the more rotations and the higher angular velocity which means more electricity supplied by
the generator. For that reason, generators are made to reduce power fluctuations to minimise
losses in transmission. The relationship between power output of a wind turbine and steady
wind speed can represented by the following power curve in Figure 6 (Wind Power Program,
2016):
Figure 6: Typical Power curve for a Wind Turbine (source: Wind-Power-Program.com, Wind Turbine
Characteristics)
1. Cut-in speed
Still, blades can only start rotating and the turbine generating electricity at minimum wind
speed. This is the cut-in speed, which is usually about 4 to 5 m/s, from which point the blades
start rotating and the generator producing electrical power.
2. Rating speed
After reaching cut-in speed, power production increases rapidly with wind speed. This is until
rating speed. This is usually set to approximately 15 m/s,for whichthe power output is maximal
and is kept level. However, this varies from model to model, and determines the choice of
model to use.
The output is managed by changing the pitch of blades to limit efficiency of lift force from the
curved shape of the blade as wind speed continues to increase.
3. Cut-out speed
If the wind speed is too high, usually greater than 25 m/s,they are considered gail force winds.
In this case, it’s too fast for rating speed power and a braking system is used to turn off power
production. This gives smoother and more predictable power production which protects the
components by reducing stress. Protecting the turbines by decreasing wear and tear is
essential to prolonging the turbine’s life span to 20 to 25 years on average.
So the choice of turbine model is chosen to suit the mostcommonwind conditions in that area.
For example, wind speeds must exceed the device’s cut-in speeds most of the time and
frequently match the rating speed.

7. 7
According the European Wind Energy Association, over this time a turbine runs nonstop for
around 120,000 hours. Although, the power generated by a turbine depends with size and the
wind speed, large turbines can produce over 6 million kWh in a year which is enough to power
1,500 average households with electricity a year without any CO2 emissions (EWEA, 2005-
2016).
2.3 The Power Efficiency of a HAWT
For a wind turbine, ideal conditions are when the wind is blowing normal to the turbine. The
wind speed decreases from upstream to downstream of the turbine (ei. Vout < Vin). This is due
to a transfer of kinetic energy (KE) from the incoming wind to mechanical energy which powers
the turbine.
Thus, using KE equation
𝐸 𝑚𝑒𝑐ℎ𝑎𝑛𝑖𝑐𝑎𝑙 = 𝑚 ×
𝑉𝑖𝑛 2 −𝑉𝑜𝑢𝑡2
2
(1)
and by definition power is
P =
𝐸
𝑡
(2)
So by replacing mass by mass flow rate in (1) we have:
𝑃 𝑚𝑒𝑐ℎ𝑎𝑛𝑖𝑐𝑎𝑙 = 0.5
𝑑𝑚
𝑑𝑡
𝑉𝑖𝑛
2
− 0.5
𝑑𝑚
𝑑𝑡
𝑉𝑜𝑢𝑡
2
However, in order for the wind turbine to use all the KE available from the incoming wind the
outlet velocity of the wind would be reduced to nothing. This would infer that air would stop
just behind the turbine. Obviously, this would cause a build-up of still air and would prevent
anymore wind flowing through the wind turbine forcing it to stop spinning. Fortunately, this
phenomenon is not possible in reality, but it does means that wind turbines have a limit to their
efficiency.
This limit is known as the Bentz limit and is purely theoretical due to the conditions in which
wind flow is normal to the turbine and the whole area swept by the blades. Thus, is in this
approximation many important factors to consider are irrelevant, like the number of blades for
example.
Bentz limit can be derived, knowing that the mass flow rate is given by:
𝑑𝑚
𝑑𝑡
= ρ Q = ρ A 𝑉𝑡𝑢𝑟𝑏𝑖𝑛𝑒
Where ρ is the specific density of the fluid, Q the volumetric flow rate, V the velocity, A the
area of the rotor disc.
but 𝑉𝑡𝑢𝑟𝑏𝑖𝑛𝑒 =
𝑉𝑖𝑛 +𝑉𝑜𝑢𝑡
2
and is approximately the average of the incoming and outward wind
velocity.

8. 8
Figure 7: Stream tube of the incoming wing through a wind turbine. The flow rate stay constants so the velocity
mustdecrease as the area increases beyond the rotor disc.(Sourece: http://www.turbinesinfo.com/horizontal-axis-
wind-turbines-hawt/)
Moving fluid must conserve its energy, so the mass flow rate is the same at input and outlet:
𝑃𝑚𝑎𝑥 = 0.5
𝑑𝑚
𝑑𝑡
(𝑉𝑖𝑛
2
− 𝑉𝑜𝑢𝑡
2
) (3)
Data has shown that the ratio of upstream and downstream velocities
𝑉𝑜𝑢𝑡
𝑉𝑖𝑛
, is max at
𝑉𝑜𝑢𝑡
𝑉𝑖𝑛
=
1
3
.
Therefore, the power is max for 𝑉𝑜𝑢𝑡 = 3𝑉𝑖𝑛.
Substituting these into (3): 𝑃𝑡𝑢𝑟𝑏𝑖 𝑛 𝑒 = 0.5
𝑑𝑚
𝑑𝑡
(𝑉𝑖𝑛
2
− 3𝑉𝑖𝑛
2
) (4)
𝑃 =
𝜌𝐴( 𝑉𝑖 + 𝑉𝑜)
2
(𝑉𝑖2 − 𝑉𝑜2)
2
𝑃 =
1
4
𝜌𝐴 ( 𝑉𝑖 +
𝑉𝑖
3
) × (𝑉𝑖2 −
𝑉𝑖2
32 )
𝑃 =
8
27
× 𝜌𝐴𝑉𝑖3
Therefore the efficiency is η =
𝑃𝑡𝑢𝑟𝑏𝑖𝑛𝑒
𝑃𝑎𝑣𝑎𝑖𝑎𝑙𝑎𝑏𝑙𝑒
=
8
27
×𝜌𝐴𝑉𝑖3
1
2
×𝜌𝐴𝑉𝑖3
=
16
27
= 59.26%.
However, this limit is purely theoretical and is dependent on ideal conditions met by the wind
and the entire area swept by the rotor.
In reality, the stream tube (Figure 7) has a diameter that is significantly smaller than that of
the turbine blades. Which means that the turbine can’t absorb energy from the wind flowing
through the whole circular surface area that the blades cover when rotating.
In addition to this, strong materials required to enable the turbine to keep running over for
many years tend to be heavy and require more force to make them spin. Even with research
into making them as light as possible they still require more force to move than lighter, but
more fragile options, which creates extra losses.
Finally, the generator converts roughly 90 – 95% of the mechanical energy it receives from
the spinning shaft into electricity, at best. Consequently, the real Bentz limit is lies between 35
- 45% for the most efficient designs. Still there are other inefficiencies that need to be
accounted for such as bearings and power transfers, erosion and dirt accumulated on the
blade over time. Subsequently, only 10 – 30% of the power from the incoming wind is
converted into usable electricity.

9. 9
As a result, the efficiency, or power coefficient, of a wind turbine varies around 20% for the
most effective turbines. In comparison, most conventional fossil fuel power stations have
capacity factors between 50% - 80% of their theoretical maximal capacity.
2.4 Wind turbine design
As with many challenges within the engineering industry, greater efficiency and higher
performance comes at a great cost - quite literally.
When designing a wind turbine, laboratory experiments tell engineers how to measure a
blade’s aerodynamics from unlimited designs and advanced materials on small scales.
However, on projects such as a wind turbine, costs add up fast and become a constraint to
attaining optimum performances. This is simply because the cost of using best materials on
sucha big scale would outweigh the amount of money made from an operational wind turbine.
Hence, final designs are always a compromise between aero dynamical performance of the
blades, mechanical strength of the materials and above all, the cost.
2.4.1 Hub and Tower design
2.4.2 Designing the blades
Shape
There are two main groups of blade shapes, they can be flat or curved.
Flat blades are the original design found on windmills. They are cheaper and easier to design
and make.They are usually drag based and rotate in the samedirection as the incoming wind.
However, they are not very productiveand are not able to competeon the commercialmarket.
The curved shape, or aerofoil, is purely performance driven to be as aerodynamic as possible,
this means that the design is not compromised by the additional costs. They are designed to
capture as much wind energy as possible in one direction. In the other, they are streamlined
to keep the rotors spinning effectively by limiting drag.
Today all commonturbines are designed to have an aerofoil cross sectionacross their blades.
This is what creates a lift force to move the blades as the wind travels over it. It’s this lift force
that gives the blades the rotation it needs to supply the generator as discussed in section
2.1.2. Aerofoils are designed using the latest technology and is always evolving, which makes
them very expensive. This is when the coupled yaw system and blade tilting mechanism come
into play by allowing the blades to always be adjusted to point directly into the direction of the
mostdominant wind to take the full advantage of this shape. This increases overall productivity
rates significantly more than other cheaper designs. In which case, investing in a more
expensive blade is worthwhile on a commercial scale where energy production is enough to
outweigh their initial cost.
Numbers of blades
The number of blades is another parameter that affects a wind turbine’s efficiency. The more
blades the more energy can by captured, more force, more productivity. However, blades are
very expensive to manufacture. Furthermore, tests have shown the efficiency increase per
blade added, lessens the more blades are added.
For instance, having four blades only makes the machine 0.5% more efficient than with three
blades, but three blades are 3% more effective than having two. Therefore, the benefit of

10. 10
having a fourth blade would not justify the cost, particularly as the more blades the thinner the
roots and would need to made from stronger the material, and all in all not worth the extra cost
(Learn Engineering, 2014).
On the other hand, in order to get a two bladed turbine to compete with 3 blades, blades would
have to spin a lot faster which would make them very noisy. Alternatively, in this case, the
chord of the aerofoil could be doubled. However, that would be just as expensive as adding
an extra blade, so it is pointless. Therefore, three blades are generally used as yet another
compromise between cost and productivity and again between aerodynamics and structural
strength (Learn Engineering, 2014).
Blade length
By definition of moments, the longer the blade,
the more torque can be applied which would
generate more power from more rotation of the
blades.
As shown by the power equations for wind
turbines power output increases proportionally
to the area swept by the blades. So logically,
blades tend to be getting longer, in order to
produce more power as time goes on. This
process is demonstrated in Figure 8, where the
average blade length significantly from 1980 to
2005.
These days, most common modern wind
turbines have diameters of 40 to 90 meters, with a three blade assembly weighing around 40
tons and produce between 500 kW and 3 MW.
That said, as of 2014 it is no coincidence that the world's mostpowerful onshore turbine, rated
at 8 MW also happens to have the record breaking long blades. The Vestas V-164 has a rotor
diameter of 164 m, consequently sweeping and area of 21,124 𝑚2. Each blade weighing 34
tons. (Sanne Wittrup, 2014)
Admittedly, lengthening the blade raises more concerns. First, it would mean a significant
increase in mass of each blade which would make the hub and the rotors too heavy for the
tower to support. Second, the longer the rotors, the more likely they are to deflect under the
axial force from the wind. This deflexion in the blade could either cause it to snap or bend
enough to touch the tower and break. Another aspect to consider is that long blades tend to
create more noise despite efforts to design quieter shapes. Last of all, blades are made in one
piece which means that very long blades are particularly difficult to transport from factory to
the site (as seen in Figure 9).
Figure 9: Transporting a wind turbine tower and blade from the factory to the Fullabrook wind farm, UK
Figure 8: Correlation of increasing rotor diameter and power rating
throughout the last 30 years

11. 11
It’s important to point out that only the amount of electricity generated by the turbine increase
with blade length. The bigger ones are not any more efficient than they’re smaller peers. They
are just larger and require more space to run.
Blade materials
On one hand, wind turbines mustbe strong enough to cope with a high exposure harsh winds.
On the other, a key part in their efficiency relies on them to be light enough to react and spin
in weaker wind conditions. All while keeping costs down as much as possible. That’s why, the
choice of material is such a critical part of designing the device.
Material properties play a key part in wind turbine performance for several reasons. First, the
material must be resistant to daily wear and tear received from strong winds. Bearing in mind,
these devices must have a life span of 25 years to make them economically worthwhile, the
choice of material is rather limited. Second, increasing blade length to produce more power is
also a current topic of debate, therefore hunt for high strength to weight materials is also in
order.
Composites are usually used in the wind sector to take on this challenge. They are made to
be strong for their weight and are usually made up of two different materials. These are high
strengthening fibres and matrix which binds and surrounds them (Conti-Ramsden, 2015).
The most commonly used fibre and least expensive, is fibre – glass is used because of its
stiffness and strength. However, it is quite dense, by using fibre glass blades a wind turbine's
total mass becomes approximately the cube of the radius of the rotor. Thus, lengthening the
blades would put a considerable amount of stress on the rest of the structure. As a result, it
an unsuitable solution for future blades, because they would simply be too heavy to be
supported by the rest of the tower.
Polymers are often used for the matrix because they are fairly light. The matrix controls many
mechanical properties of the composite such as the fracture toughness, the delamination
strength, out of plane strength, stiffness and influence of fatigue life on the composite.
Typically, thermosets such as epoxies, polyesters, vinylesters are used. Although,
thermoplastics have the advantage of being recyclable, they far more energy demanding to
make due to the high viscosity of the melt that they are made from.(National Research Council, 1991)

12. 12
2.4.3 Wind turbine overall expenses
All in all, a typical commercial scale wind turbine, generates around 2MW and costs around
£2.5 -3 million in total to install. It should recover the equivalent of its initial carbon footprint
from its materials, manufacturing, transport and installation, with clean energy production
within 6 to 8 months (EWEA, 2005-2016). It then takes anywhere between 5 to 6 years to pay
back for its initial cost by selling the electricity generated to the grid.
Given that it’s lifespan should exceed 20 years, it spends around ¾ of its operational lifetime
making profit, although this does exclude unpredictable maintenance issues. Therefore, the
total 'pay back' time, depends on wind consistency and the price of electricity. Hence, there is
a lot of profit making potential in this developing industry. This ought to attract more investment
from growing energy companies in the near future.
2.5 Study case: Den Brook wind farm
First Wind Farm in the UK opened in the South Westof England in Delabole 1991. It consisted
of 10 turbines and produced enough to power 2,700 homes. Since that day, others have
opened in the region including the Den Brook Wind Farm recently finished near Torquay.
Den Brook Wind Farm is an 18 MW Wind Farm (Renewable Energy Systems Ltd, 2016) in
Devon which became operational in October 2016. It is made up of 9 Vestas V80 -2 MW
turbines financed by RES who developed and constructed the wind farm. The wind farm has
since been acquired by Aviva Investors, the global asset management business of Aviva plc.
Den Brook is also applicable for the Renewables Obligation* support mechanism.
The land is leased from a number of landowners. The planning permission is for 25 years
which reflects the approximate lifetime of a wind turbine. The original project planned for 10
turbines but was reduced to 9 turbines. The reduction in the size of the wind farm by one
turbine was made on the advice of planning officers during the development phase of the
project. Vestas V80 are designed for regular moderate to high wind speeds and are one of
2,800 models currently in use.
Interestingly, the models used for the Den Brook project had an extra 20m was added to each
tower (from 60m to 80m), thus increasing the overall heights to 120m ground to rotor tip. The
aim being to enable each one to capture more wind and make them more effective while
keeping the same rotor diameter as the original Vestas V80 design of 80m diameter rotors.

13. 13
Figure 10: Power Curve of the Vestas V80 on the Den Brook Wind Farm in Devon (PIERROT, 2016)
As seen, in Figure 10 above, theses turbines start generating power with wind speeds greater
than 4 m/s which is the cut in speed and plateau at a rating speed of 15 m/s, average mean
wind speed in the area is 13.4 knots (or 7 m/s) but with regular gusts between October and
January exceeding 70 knots (36 m/s) (Met Office, 2016) for which the device is protected by
its braking system when gusts exceed 25 m/s.
The 18 MW site should generate enough electricity to power 9,000** UK homes and should
provide the local community within a 2.3km radius of the turbine with a £108 annual saving on
their electricity bills a year. As well as, contributing £36,000 each year the community fund to
support local projects. So overall, the communityshould benefit from £90, 000 per year thanks
to the project. An unexpected additional benefit was a link road to Whiddon Down which is
now open. It was used to transport turbine parts to the Den Brook site but has helped to reduce
traffic congestion in the area. Worth pointing out that this would not have happened otherwise
because it is a rural area not well kept. The energy yield data for the farm has not yet been
released as it is such a new project.
However, despite all these apparent benefits there was a lot of resistance from locals to install
the farm. At its inception in the mid-2000s, people were reluctant to join in the project before
it was finally given planning permission in 2009 and construction started in August 2015 to
first operate in October 2016. It turned out many, were worried that the farm would be noisy
and disturb the rural neighbourhood (Den Brook Judicial Review Group (DBJRG), 2010).
One man in particular invested over £100,000 of his own money to oppose the installation of
the wind turbine farm. This conflict of interest even captured the attention of the BBC who
made a four-episode documentary on the development of Den Brook Wind Farm. Which was
broadcasted between May and June 2011, called Wind Farm Wars. Including face-to-face
interviews with a number individuals concerned with the windfarm, it focused primarily on
Rachel Ruffle, project manager for RES, and Mike Hulme, local resident and member of
DBJRG.
There is a complaints process in place made direct to the local planning authority, WestDevon
Borough Council, for which the details of complaints remain confidential. RES has hosted a
number of visits to the wind farm over the last few months and have received predominantly
positive feedback during these visits from a range of local stakeholders such as North Tawton
Community Primary School. In an effort to stay in touch with the local community, RES
administers a Community Liaison Group for Den Brook Wind Farm which has been very
successful.

14. 14
*The Renewables Obligation (RO) is one of the main support mechanisms for large-scale
renewable electricity projects in the UK. […] The RO came into effect in 2002 in England and
Wales, and Scotland, followed by Northern Ireland in 2005. It places an obligation on UK
electricity suppliers to source an increasing proportion of the electricity they supply from
renewable sources.’ (Office of Gas and Electricity Markets, 2016)
** based on the wind farm’s predicted energy yield of 37.55GWh and the 2013 UK average
annual household energy consumption to be 4128kWh from data published by the Department
of Energy and Climate Change.
3 Discussion
One of the main reproaches faced by wind turbines today is their lack of power efficiency. At
30% efficiency at best, they are well behind other current leading energy sources, particularly
those powered from fossil fuels. However, ways of increasing their overall power output are
becoming more and moreattainable. In particular, blades in new models are looking to exceed
100m in length. Lots of research is focussing on finding a new kind of material with the best
combination of high strength to low weight ratio material for blades, as well as, long lasting
materials and coatings to produce prolong the device’s lifespan. While staying reasonably
priced.
3.1 How to enhance wind turbine designs?
Some are already experimenting with carbon fibre blades, because they are somewhat
stronger than fibre-glass and much less dense could solve this issue. Unluckily, it a lot more
expensive to buy and to handle when manufacturing. These statements are made obvious
from Figure 11, that compares the density, strength and cost of different fibres used to build
wind turbine blades
Yet, another important point to account for is that by having lighter blades the tower and the
rest of the turbine components do not have to be as strong and stiff to cope with any excess
weight. Therefore, in somecases,the extra costof investing carbon fibre could be outweighed
by the additional power that can be produced by the extra length in the blades, as well as, by
cutting the costs of the materials for the rest of the turbine.
Figure 11: ACP Composites fibre matrix comparison ( ACP Composites, 2010)

15. 15
For instance, the particular case of the Vestas V112-3MW is an excellent example of this case.
The device has three carbon fibre blades that are 54.6m long (while the norm is 40-45 m long).
By using carbon fibre, Vestas were able to make them longer for the same weight as their
shorter fibre glass models. This enables, the blades to sweep a bigger area by about 55%
which increased the wind turbine production and the company’s revenue. More surprisingly,
the company even saved money on building a less sturdy tower with cheaper material.
Other improvements involve using carbon fibre in specific areas of the spar, to blades any
longer than 45m. The spar caps run along the length of the blade and can be integrated into
the shell of the blade, as shown below in Figure 12. This alone can make blades stiffer and
lighter by about 20 % than if made all fibre glass (Gardner Business Media, 2016) without
making it much more expensive.
Figure 12. Spar made of Carbon fibre within a blade made of fibre glass
Other properties of the materials are also being explored. Scientists are currently looking into
the chemistry behind curing composites to make them tougher. This is a particular interest of
a research activity called BLEEP(blade leading edge erosion program). The program is aimed
at finding a way of prolonging the life of the leading edge of a turbine blade, because it suffers
highest level of erosion of the turbine because it ‘cuts through the air’. This along with
accumulated dirt and will make the blades rougher over time and compromise the
aerodynamic efficiency of the blade and decrease the efficiency overall power output. (Conti-
Ramsden, 2015).
3.2 Are these technological improvements worthwhile?
However, ultimately the goal to design a wind turbine makes more money than it costs as soon
as possible. So given that fibre-glass is so easily available, any other materials depend on the
balance between cost and performance and most companies will compromise the choice of
material in order to get a wind turbine running over waiting. Gary Kanaby, the director of sales
for wind energy, sums this up in a quote by “It doesn’t really matter what it’s made out of when
it’s spinning,” he says. “It just needs to make money.” ( ACP Composites, 2010)
How could challenges faced by wind turbine developers be overcome?
Wind turbine farms are surprisingly hard to site at the best of times. They rely regular wind
flow in open spaces to reduce turbulence from the surrounding topography. However, such
places are hard to find and as for any construction project require planning permission from
the local council and the surrounding community.
Surprisingly, it is usually the latter that are preventing morewind farms from being established.
This stems from the fact that, society has mixed views about them. As ever, some are more
objective than others. Although some people see wind turbines, as technological progress
towards a greener and more sustainable future, others see them as an artificial intrusion on a

16. 16
rural landscape. The main reservation that people have against wind turbine farms is their
reputation for being noisy, whichwould bother to nearby communities.However, this complaint
is no longer relevant. The all modern designs are made with a particular emphasis making the
blades quasi silent under usual conditions with to low - moderate wind speeds. A solution to
these issues, is using offshore wind turbines instead. Thus, out at sea the infrastructures
cannot be seen, nor could any noise cause any disturbances. However, they are pricier to run
because they are exposed to harsher weather conditions, with higher levels of corrosion and
are difficult to access for maintenance. That said, offshore wind energy is central topic of
research at present.
Finally, as with all tall structures with moving parts and high voltage equipment turbines there
is inevitably a concern for public safety and harming wildlife such as migrating flocks of birds.
(Daniels, 2005).
So why invest in wind energy if there is so much opposition?
First wind energy is often criticizedfor its lack of efficiency comparedto other renewable power
sources, but wind turbines stand out from other forms of environmentally friendly energy
because they don’t produce any waste or any greenhouse gases throughout their lifespan.
They can also be dismantled once they can no longer be used. Plus, any power they produce
is completely renewable because it comes from the wind which is natural, free and abundant.
As for the Den Brook Wind Farm, they can also be built on existing farms, so sites can double
up for grazing livestock and producing electricity and no need to clear spaces unnecessarily
by deforestation for instance.
From an economic and social point of view, wind energy is one of the cheapest sources of
renewable energy as new windfarms are now on average £20 cheaper per megawatt hour
than coal or gas-fired plants (Ethan Zindler, 2015). Plus, as a growing business, wind farms
also create jobs. In addition, most turbine farms offer a local benefit scheme which ensure
annual discounts to locals on their annual electricity bills. A bigger future investment in this
industry would produce a greater multiplier effect, and make it even more affordable.
Installing wind turbines in remote places doesn’t only profit communities by providing cheaper
power through subsidy schemes. There are also additional benefits such as promoting
accessibility to cut off areas. Wider and straighter roads are often repaired or built, to fulfil the
need for to transport such large and expensive parts from the factory to the site. Such as the
Whiddon link road in Devon, which has been opened and is now used to help traffic circulation
in the area. This is a place where the maintenance country roads could not keep up with the
increasing number of cars in the region.
Taking example from the Den Brook project, using basic design aerofoil blades, average
blades with a rotor length 40m long, made of fibre glass. Simple seems to be better for many
projects. Although, the design height adapted to the site by adding an extra 20m to the tower.
It seems that despite not investing in the latest improvements by using carbon fibre or longer
blades the site has still massively helped the local community. The project overcame many
years of resistance by making an immense effort of involving the locals and providing directly
with the financial benefits from the turbine.

17. 17
4 Conclusion
Wind turbine technology has come a long since the original design in the late 1890s and even
since the 00’s. Although it’s efficiency may be limited in comparison to other power sources, it
one of the very few that can boast that the power it generates is completely renewable once
installed and even its manufacturing has a relatively low carbon footprint.
Wind energy is becoming more and more affordable and its efficiency is increasing with
technological progress over time. Many apprehensions, about the using wind turbines come
from the earlier models which had many design flaws, such as noise for example, but most
are no longer relevant to modern designs.
As discussed previously, designing wind turbines to include all the necessary properties is an
expensive procedure. Consequently, compromises are always being made with the ultimate
goal of always generating enough electricity to outweigh the initial cost to design.
Much ongoing research into making designs more effective and efficiency is a good sign for
the future. However, when taking into account the current environmental awareness,
economic and social climate a need for clean energy is becoming more urgent and changes
must be made soon.
A solution to this could be to invest less money into research on enhancing the properties and
consequently making more expensive wind turbine models. Conversely, redirect it into
educating and supporting local projects. New projects need support from the local residents
in order to start up and more notably last. By spending more money on communicating the
urgency of climate change and the benefits of green energy and how easily accessible it is,
more projects could take place. Also, involving the public more and making them a part of a
wind farm success they are more likely to promote green energy elsewhere.
Prioritising communication over cutting-edge technological improvements until the people are
open to invest the change and are ready for a bigger leap will pay off. In order to secure a
greener future renewable energy sources cheaper and easier to use that the traditional fossil
fuel ways already in place. Then once a competitive market is in place there will be room for
further investments in high-tech enhancements.

18. 18
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