Wind Energy
• A windmill usually refers to the use
of mechanical energy from the wind
for pumping water or milling grain.
• A wind turbine converts the
mechanical energy of the wind into
electrical energy.
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Wind Turbines
• The most common wind turbine
design is the horizontal axis wind
turbine (HAWT).
• Other designs have been
proposed, but have not been
widely commercialised.
• The blades of a modern wind
turbine are designed similarly to
aircraft wings (called an airfoil).
• The aerodynamic flow of the wind
over the blade generates “lift”
which spins the blades around.
• They are on a high tower to capture the fastest, least turbulent
winds.
A nice introduction to wind turbines:
https://science.howstuffworks.com/environmental/green-science/wind-power.htm
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Components of a Wind Turbine
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Components of a Wind Turbine
• The nacelle houses the operational components supporting the
electricity generator of a wind turbine.
• The gearbox turns the slow rotation of the blades into a quicker
rotation that is more suitable to drive an electrical generator.
• An external anemometer is responsible for measuring the
incoming wind speed and wind direction. The wind speed data
will be used to control whether to shut down the wind turbine
for safety or emergency concerns and the orientation of the
rotor or blades.
• The pitch system turns (or pitches) blades out of the wind to
control the rotor speed, and to keep the rotor from turning in
winds that are too high or too low to produce electricity.
• Located on top of the tower and connected with the nacelle, the
yaw system aligns the turbines towards the wind.
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Size of Wind Turbines
• The larger the area swept
out by the blades, the
more energy from the
wind that can be
captured.
• But the larger the turbine
the greater tip speeds and
mechanical stresses on
the system.
• There are also increased
challenges around
transportation and
construction for such
large structures.
5
Power Generated
• The power available from wind is:
Pwind = Av
1
2
3
 = air density kg/m3 (dry air ~1.2 kg/m3)
A = area swept out by blades (m2)
v = wind speed (m/s)
• The performance of a wind turbine is characterised by it’s power
coefficient:
Pturbine
Cp =
Pwind
• The maximum theoretical power co-efficient for an ideal turbine is 0.59.
• The 0.59 factor comes in from an aerodynamic analysis by Albert Betz
(1919) – Betz’ Law. It assumes an infinite number turbine blades and
no frictional drag as well as a number of other idealised assumptions.
• You never convert more than 16/27 (or 59%) of the kinetic energy in
the wind to mechanical energy using a wind turbine.
• In practice, the maximum power coefficients achieved are 0.4-0.5.
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Power Generated
• The power generated is related to v3. Small increases in wind
speed give big increases in the power available in the wind.
E.g. 10% increase in wind → 30% increase in power.
2x the wind speed → 8x the power.
• The precise location of turbines relative to local topographical
features is very important – not just the regional wind patterns.
• The best wind resources are available in off-shore locations.
• Off-shore locations also can reduce environmental effects and
community concerns.
• The additional problems with
corrosion protection,
construction and maintenance
costs and more difficult grid
connection means that most
wind farms are constructed
on-shore.
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Wind Power
• The power curve
shows the power
output as a function of
the wind speed.
• Wind turbines are
designed to start
running at the cut-in
wind speed (usually
around 3-5 m/s).
• The wind turbine will be programmed to stop at high wind speeds
in order to avoid damaging the turbine or its surroundings. This is
the cut-out wind speed (usually around 25-30 m/s).
• They will also be designed to have maximum power at a
particular wind speed – the rated wind speed.
• The capacity (rated power) of a wind turbine will be the power
output when operating at the rated wind speed or above.
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Example – Enercon E112-4500
•
•
•
•
An offshore wind turbine.
Capacity of 4500 kW = 4.5 MW.
Rotor diameter: D = 114 m.
Tower 120 m high.
Cut-in wind speed 2.5 m/s
Rated speed 14 m/s
Cut-out speed 25 m/s
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Example – Enercon E112-4500
For a wind speed of 9.0 m/s, how much power is available in the
wind for this turbine? What is the power co-efficient at this wind
speed?
Pwind = 12  Av3
A =  r 2 = 3.14159  (114 / 2) 2 = 10, 207 m 2
Pwind = 12 1.2  10, 207  93
= 4, 464,557 W = 4, 465 kW
Pturbine
Cp =
Pwind
2, 000 kW
=
4, 465 kW
= 0.45
from
previous
graph
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Power output for Wind
• Most of the time the wind speed will be below the rated speed
and so the power output will also be less than the capacity.
• Because of the v3 dependence on wind speed, it is not correct to
use the average wind speed to calculate the average power
output – the distribution of wind speeds at a particular site must
be taken into account.
• Wind speed distributions can often be modelled with a function
called a Weibull distribution.
Weibull Distribution
• So the average power
  v 
 k  v 
f (v) =    exp  −   
output would be:
c c
c
k −1

Pavg =  P(v) f (v)dv
  
k
  
0
P(v) is the power curve.
• This mathematics is beyond
the scope of this course.
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Capacity Factors for Wind
• In this course we will rely instead on reported capacity factors for
wind turbines.
• In Australia, the typical capacity factor for installations is 30-40%.
• Capacity factors of wind farms have generally increased.
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Wind farms
•
•
•
•
•
A wind turbine takes energy from the wind – it slows it down.
It will cast a “wind shade” or “wake” in the downwind direction.
Ideally we should space turbines out as far as possible.
Land use and grid connection prevents this.
Spacing turbines ~ 8 - 10 rotor diameters apart in the prevailing
wind direction, and ~ 5 diameters in the crosswind spacing will
limit these array losses to less than 10%.
Macarthur Wind Farm, VIC
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Wind fluctuations
• There are many different causes of wind fluctuations.
Cause
Time Scale
Remedy
Gusts
Seconds
Wind Farm
Diurnal cycle
Daily
Distributed system
Inversion layers
Hours
“
Weather patterns
Hours to days
“
Seasons
Months
Annual variations
Years
<10%
• Fluctuations in the supply from wind will require an electricity network to
have a greater amount of “spinning reserve” or other storage.
• Required to match demand, and to avoid frequency fluctuations.
• This may limit the short-term penetration of wind into the system or
result in increased reliance on gas generation (in Australia).
• The low cost of wind in low-demand periods forces conventional
generators out of business.
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Case Study – Sapphire Wind Farm
• Opened 2018, largest wind farm
currently operating in NSW.
• Capacity: 270 MW, using 75
turbines of 3.6 MW each.
• Turbine blade diameter = 126 m.
• Capacity Factor
= 34%.
Data from: http://energy.anero.id.au/wind-energy
• Project Value
= $590 million.
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Case Study – Sapphire Wind Farm
Approx. land area required:
- Spacing 5 and 8 rotor diameters apart:
Each turbine area = (5 x 126) x (8 x 126) =635,040 m2 = 0.64 km2
Total area = 75 x 0.64 = 48 km2
Annual Output:
Actual Output
Capacity Factor =
Maximum Possible Output
Actual Output (MWh)
0.34 =
270 MW  (365.25  24) h
Actual Output (MWh) = 0.34  270  365.25  24
= 804,720 MWh
= 8.05 108 kWh
(Compare to Eraring = 1.3276x1010 kWh, i.e. ~16x higher)
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Sapphire – Generation Cost Estimate
Assume 25 year lifespan and 2% running costs.
Total 25 year cost = $590 million + 25  0.02  $590 million
= $885 million
Total 25 year cost
Cost/kWh =
Total 25 year output
$885 106
8.05 108 kWh  25
= $0.044/kWh
= 4.4 cents/kWh
Wind is has been a rapidly growing area of renewable energy
generation in Australia and worldwide.
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Wind Variability in the NEM
Black – NEM (not WA), Red – Sapphire Wind Farm
Low periods of wind are often a widespread occurrence.
http://energy.anero.id.au/wind-energy
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Other Considerations
• Most current wind generators do not provide system strength
and system inertia – they are not able to maintain stable
network voltage levels and system frequency.
• Aesthetics.
• Health impacts of infrasound (??)
• Wildlife impacts and ecosystem fragmentation.
• Resources for construction and end of life disposal
https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2019/Oct/IRENA_Future_of_wind_2019.pdf 19
Wind Power - Australia
• At 2021, nationally over
9000 MW (9 GW) of
installed wind capacity.
• 11.3 % of electricity
generation in 2021.
• Several new large wind
farms in planning.
• Because of local topography, some
local sites may have a higher wind
speed than the regional average.
• Availability of existing distribution
networks or cost of constructing a
new network are significant for the
economic viability of wind.
Average wind speed (m/s).
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Wind Power – Global
Electricity generation by wind has been steadily growing, but not
accelerating in recent years.
https://www.ren21.net/reports/global-status-report/
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Hydroelectricity - Global
In many countries hydropower is a major
contributor to electricity generation.
Share of global hydropower capacity by country
https://www.ren21.net/reports/global-status-report/
IEA Key World Energy Statistics, 2021
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Hydroelectricity - Australia
• 8500 MW installed capacity in 120 different hydroelectricity
plants, mostly in Tasmania and as part of the Snowy Hydro
Scheme.
• 7.8% of our electricity generation in 2021.
• Hydroelectricity is flexible and dispatchable.
• There are no conventional hydroelectricity projects planned.
Lack of water resources and ecosystem conservation are
significant barriers.
• There are proposals to upgrade the interconnector to
Tasmania so that those existing resources can be better
optimised to meet peak demand in the NEM.
• However, pumped storage hydroelectricity is now being
considered. Snowy Hydro 2.0 is a pumped storage project and
there are numerous proposals for smaller projects.
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Hydroelectricity
GPE = mgh
• h is called the head.
• Modern hydroelectricity is
~ 80-90% efficient in converting the
PE of the water into to electrical
energy.
• 1 litre water ≈ 1 kg.
• 1 m3 water ≈ 1000 kg.
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Example
Calculate the flow rate of water required to produce 1 kW of electric
power if the water falls a distance of 20 m. Assume an 80%
conversion efficiency of the hydroelectric generator.
Step 1: Use efficiency to
determine power required
from source.
Output
Efficiency =
Input
1000 W
0.80 =
Input
Input = 1000 / 0.8
= 1250 W
= 1250 J/s
Step 2: Amount of water to
provide this power.
Consider a time frame
of 1 second.
PE = mgh
1250 = m  9.8  20
m = 1250 /(9.8  20 )
= 6.4 kg
i.e Need a flow rate of 6.4
kg/s = 6.4 litres/sec.
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Snowy Mountains Hydro Scheme
•
•
•
•
•
•
3950 MW hydroelectric power.
4,500 GWh average annual output (4.5x106 MWh).
You can show that this gives a 13% Capacity Factor.
Operates as a peak-demand facility.
Took 25 years to build (1949-1974)
16 dams, 7 power stations (33 turbines), a pumping station, 145
km of tunnels and 80 km of aqueducts.
• Recently undergone a $400 million maintenance/refurbishment.
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Three Gorges Dam Hydroelectricity
• World’s largest
hydroelectricity
scheme.
• 22,400 MW
Capacity.
• ~95,000 GWh per
year
• US ~$28 billion.
• Full operation in
2012.
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Three Gorges Dam Hydroelectricity
• Replacing the burning of 30 million tons of raw coal annually.
Saving the discharge into the atmosphere of:
– 100 million tons of carbon dioxide,
– 1.2-2 million tons of sulphur-dioxide,
– 10,000 tons of carbon monoxide,
– along with particulates and fly-ash.
But…
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Three Gorges Dam Hydroelectricity
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Pumped Hydroelectricity Storage (PHS/PHES)
• Globally, this is the largest and most widely used method for storing
large amounts of energy.
• Low pollution and waste, fast response, large capacity.
• May be limitations due to geological environment and water supply.
https://www.canstarblue.com.au/electricity/hydro-power-australia/
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Pumped Hydroelectricity Storage (PHS/PHES)
• Globally, this is the largest and most widely used method for storing
large amounts of energy.
• Low pollution and waste, fast response, large capacity.
• May be limitations due to geological environment and water supply.
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PHES - Australia
• Australia has three existing pumped hydro power stations
including Wivenhoe in Queensland (570 MW), Tumut 3 (1800
MW) and Shoalhaven (240 MW), both in New South Wales.
• Snowy 2.0 is a proposed pumped-hydro expansion of the Snowy
Mountains Scheme.
– Linking Tantangara and Talbingo reservoirs with tunnels and
an 800 m underground pumped-hydro power station.
– Capacity of up to 2,000 MW,
– Storage for about 175 hours (or 350,000 MWh).
– Capital cost of $5.1 billion, expected completion 2026.
https://www.snowyhydro.com.au/snowy-20/about/
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PHES - Australia
• In 2017 an ANU study identified 22,000 possible sites for smaller
scale pumped hydro storage in Australia.
https://www.dropbox.com/s/5s5cbwcw32ge18p/170919%20PHES%20Atlas.pdf?dl=0
• A number of PHS projects have been proposed in the few couple of
years across the country but only one has started construction.
• The Kidston PHS project
commenced construction
in May 2021.
• 250 MW capacity and
2000 MWh storage.
• It re-uses old gold mining
pits for storage and is
co-located with a PV
solar farm.
• ~$770 million project
cost.
https://genexpower.com.au/250mw-kidston-pumped-storage-hydro-project/ 33
Ocean Energy
There is a vast amount of energy available in the worlds oceans,
but little of it has been captured. It is renewable and relatively
predictable. The main categories of ocean energy are:
• Ocean thermal energy conversion (OTEC). Warm sea
water vaporises a working fluid or flash evaporates seawater
to turn a turbine. The technology is not commercialised.
• The energy associated with the flow of ocean currents can
be captured similarly to wind turbines. This approach faces a
number of technological and oceanographic challenges.
• Tidal power has been utilised in a small number of power
stations over the decades. But tidal regions are often
ecologically sensitive to any disruption in their flow.
• Wave Power has been the focus of a variety of novel designs
and proof-of-concept projects. It has yet to demonstrate
commercial viability
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Ocean thermal energy
conversion (OTEC)
• Only suitable for tropical waters.
• Largest project so far is a 1 MW
demonstration project under
construction in Kiribait.
https://www.irena.org/documentdownloads/
publications/ocean_thermal_energy_v4_web.pdf
100 kW
operating
system in
Hawaii.
https://www.makai.com/ocean-thermal-energy-conversion/
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Tidal Power Technologies
Tidal Barrage
Tidal
fence
Tidal Turbine
https://actionrenewables.co.uk/news-events/
post.php?s=everything-you-need-to-know-about-tidal-energy
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Case Study - Sihwa Lake tidal power station
https://www.hydropower.org/blog/technology-case-study-sihwa-lake-tidal-power-station
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Wave Power
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Ocean Energy Status
• Total additions to global ocean energy in 2021 were around 2
MW.
• This brings the total global operating installed capacity to an
estimated 530 MW at year’s end (i.e. a very small amount).
• Two tidal barrages – the 240 MW La Rance station in France
(installed in 1966) and the 254 MW Sihwa plant in the
Republic of Korea (2011) – represent more than 90% of total
installed capacity.
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