Ocean Energy 1

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9/14/2015
1
Ocean and Hydro Energy
Wave Energy Power Conversion
Dr Andrew Cashman
MECH7008 Overview
On successful completion of this module you will be able
to:
� Analyse the potential of a site for ocean energy
exploitation
� Analyse the potential of a site for hydro energy
exploitation
� Assess the marine environment factors affecting
deployment and reliability of an ocean energy device
� Analyse the energy conversion techniques employed in
ocean and hydro energy systems
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Attend Class!
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
9/14/2015
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Attend Class!
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Intended Learning
Following this lecture you will be able to:
1. Discuss various turbine types as used in wave energy
conversion applications
2. Detail the mode of operation of the Impulse and Wells
turbines
3. List some of the O&M issues associated with this type
of turbine
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Introduction
Many technologies exist for converting wave energy into
electrical power. It has become clear that Oscillating Water
Column type devices are widely used and have reached
the fullscale commercial stage.
A key aspect to the performance of these OWC devices is
the performance of the self-rectifying turbines used to
convert the pneumatic power to mechanical shaft power.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
9/14/2015
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Oscillating Water Columns
The Oscillating Water Column has a number of power
conversion steps in converting incident wave power to
electrical power:
Step 1: Converting incident wave power to pneumatic
power
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Oscillating Water Columns
Step 1: Converting incident wave power to pneumatic
power
This step is completed in the OWC chamber itself. The
incident wave is captured and creates a pneumatic
pressure within the chamber.
Step 2: Converting pneumatic power to mechanical shaft
power
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Oscillating Water Columns
Step 2: Converting pneumatic power to mechanical shaft
power
In this step, the pneumatic pressure is used to create
aerodynamic power which drives a turbine. This stage is
crucial in the overall process but is currently the least
efficient part of the process!
Because the airflow is bi-directional (air is pushed out of
the chamber when waves rise but sucked in when they fall)
only certain turbines can be used in this conversion
process. These are called self-rectifying turbines.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
9/14/2015
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Oscillating Water Columns
Step 3: Converting mechanical shaft power into electrical
power
This stage is carried out using a generator which is coupled
to the turbines shaft. The mechanical torque is used to
create electrical power which can then be supplied to the
grid.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Oscillating Water Columns
OWC’s are essentially air chambers open at one end to the
water. This design allows waves to rise and fall inside the
chamber creating an oscillating column of air. This column
of air then drives a turbine which is located in a duct on
top of the OWC and this mechanical energy is converted to
electrical energy using a generator.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
One of the main advantages of
the OWC is that since the moving
parts within the plant are not in
direct contact with sea water,
maintenance is significantly
reduced.
Oscillating Water Columns
See video for demo on OWC operation
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
9/14/2015
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Self-Rectifying Turbines
Self-rectifying turbines are a vital part of the power
conversion process in OWC applications. As the airflow is
bi-directional, the turbines are required to rotate in the
same direction, irrespective of airflow direction.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines
There are many different self-rectifying turbines that can
be used for wave energy conversion. The main groups of
self-rectifying air turbine are:
1. Wells turbine
2. Impulse turbine
3. Denniss-Auld turbine
4. Radial turbine
5. Alternative impulse turbine
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Worked Example 1.1
Q1. Describe the main stages involved in the conversion of
wave power to electrical power in an OWC application
Q2. Describe what is meant by the term “self-rectifying”
turbine.
Q3. List the main types of self-rectifying turbines used in
OWC applications
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
9/14/2015
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Self-Rectifying Turbines
Wells type turbine
The Wells turbine was a concept first proposed by Prof. A.
A. Wells of Queens University, Belfast in 1976. In its
simplest form the Wells air turbine rotor consists of several
symmetrical aerofoil blades positioned around a hub with
their chord planes normal to the axis of rotation as shown.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines
Wells type turbine
Due to the rotation of the blade, the airflow relative to the
blade is at an angle known as the angle of attack. Aerofoils
produce lift at 90° to the angle of attack and which is what
drives the turbine.
Many design variations of the Wells turbine have been
developed. Both mono-plane and bi-plane turbines exist,
while studies have also been carried out to investigate the
performance of the Wells turbine with guide vanes.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines
Wells type turbine
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Figure (a) shows a monoplane Wells
turbine.
Figure (b) shows a biplane Wells turbine.
This is essentially two Wells turbines in
series
Figure (b) shows a contra-rotating Wells
turbine. This is a biplane turbine where the
second rotor rotates in the opposite
direction as the first.
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Self-Rectifying Turbines
Wells type turbine
A major disadvantage of the Wells turbine is that it suffers
from stall, i.e. a sudden decrease in Torque where the
turbine can even produce negative torque. One method
that was devised to overcome this was by allowing the
rotor blades to pivot in the airflow, limited to 10 degrees of
rotation.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines
Impulse type turbine
The impulse turbine was first designed by Kim et al. (1988)
and is based on the Euler turbomachinery theory. As air
flows over the rotor blade, the curvature causes a pressure
difference across the blade which forces the turbine to
rotate.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines
Impulse type turbine
There are a number of different guide vane assemblies
which have been used on the impulse turbine. These
include:
1. Impulse turbine with self-pitching guide vanes
2. Impulse turbine with self-pitching linked guide vanes
3. Impulse turbine with fixed guide vanes
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
9/14/2015
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Self-Rectifying Turbines
Impulse type turbine
The self-pitching type of guide vane assembly allows the
guide vanes to pivot about a point under the aerodynamic
forces. Whenever the airflow direction changes, the guide
vanes pivot from nozzle to diffuser setting angles, and vice
versa.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines
Impulse type turbine
Setoguchi et al (1996) proposed a
concept to rectify issues
associated withthe diffuser setting
angle in the self-pitching guide
vane arrangement.
Used mechanical links to connect
opposing guide vanes therefore
utilising aerodynamic moments
generated by the nozzle guide
vane to move the downstream
guide vane to the correct diffuser
setting angle.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines
Impulse type turbine
In real sea trials of the moving guide vane arrangements,
it was concluded that the large quantity of moving parts
would create operation and maintenance issues.
Therefore, a concept was proposed where the guide vane
angles upstream and downstream were made symmetrical
and were fixed to the structure.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
9/14/2015
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Self-Rectifying Turbines
Radial turbine
The Radial turbine operates in a different manner to both
Impulse and Wells turbine, where the flow is axial. Here,
the flow enters axially but is then diverted to flow radially
outwards to the tip of the turbine.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Impulse type blading
is used with fixed
guide vanes.
Self-Rectifying Turbines
Denniss-Auld turbine
The Denniss-Auld turbine is a new turbine design,
developed by Energetech in collaboration with the
University of Sydney, Australia. It is a variable-pitch
turbine that has unique operating characteristics which
sets it apart from both impulse and Wells type turbines.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
The blades are non-standard
aerofoils which are symmetric
about the mid-chord and are
allowed to pitch about the radial
axis.
Self-Rectifying Turbines
Denniss-Auld turbine
Under oscillating flow conditions, the blades are pitched
according to the sequence shown. At peak axial velocity,
the blades are pitched at maximum angle and as the
velocity decreases, so does the angle of attack. When the
direction of airflow changes, the blades flip across the
neutral position, and realign at the optimum angle of
attack for the oncoming air flow.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
9/14/2015
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Turbine Performance Comparison
So how do these turbines perform in comparison with one
another?
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
WTGV = Wells turbine with guide vanes
TSCB = Wells turbine with self
controlled pitching blades
BWGV = Biplane Wells turbine with
guide vanes
ISGV = Impulse turbine with self-
pitching guide vanes
IFGV = Impulse turbine with fixed guide
vanes
Self-Rectifying Turbines in Use
So where are these turbines being used today?
There are a number of large scale OWCs (or similar
devices) in use today at various locations around the
world.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines in Use
LIMPET, Isaly, Scotland
The LIMPET (Land Installed Marine Power Energy
Transmitter) plant on the island of Islay, Scotland was the
world’s first grid connected commercial wave energy plant.
LIMPET is an OWC type device and was initially capable of
producing 500 kW of electrical energy.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
9/14/2015
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Self-Rectifying Turbines in Use
LIMPET, Islay, Scotland
LIMPET uses a 7 blade, 2.6m diameter Wells turbine,
shown in Figure 2-5 with the outer casing removed during
assembly. This configuration is repeated and installed back
to back in order to form a contra-rotating biplane Wells
turbine.
See:http://voith.com/en/products-services/hydro-
power/ocean-energies/wave-power-plants-590.html
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines in Use
Pico Power Plant, Azores, Portugal
The European Wave Energy Pilot Plant on the island of
Pico, Azores, Portugal is another example of an onshore
OWC device. Built in 1998, this plant was rarely used over
the first few years due to a combination of technical and
financial difficulties, however, in 2003 a recovery project
was launched by the WavEC.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines in Use
Pico Power Plant, Azores, Portugal
The plant houses a 2.3m diameter Wells turbine which is
fitted with upstream and downstream fixed guide vanes.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
9/14/2015
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Self-Rectifying Turbines in Use
Pico Power Plant, Azores, Portugal
Two additional valves have been fitted to the turbine duct
area, namely a fast acting valve (2) and a sluice-gate
isolation valve (1). The sluice valve is mainly used when
the plant is disconnected over a long period of time
whereas the purpose of the fast acting valve is used to
prevent turbine over-speed when grid connection is lost in
energetic seas.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines in Use
Energetech, Port Kembla, Australia
The Energetech OWC uses a novel, variable-pitch turbine
(Dennis-Auld) and a parabolic wall behind the OWC which
focuses the wave energy on the collector.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Both fixed on-shore and
floating offshore devices are
being used.
Self-Rectifying Turbines in Use
Vizhinjam OWC, India
In 1991, a 110 kW demonstration plant was built in
Vizhinjam, South India, by the National Institute of Ocean
Technology (NIOT).
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
9/14/2015
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Self-Rectifying Turbines in Use
Vizhinjam OWC, India
A 1m dia Wells turbine was tested but in 1996 was
replaced by an impulse turbine with self-pitching guide
vanes due to encouraging results on the potential of this
impulse turbine. Among the several power modules
tested, the best performance was obtained using the
impulse turbine.
Maeda et al. (1999) proposed the use of fixed guide vanes
with optimum angles due to the elimination of
maintenance of the extra moving parts, operating life
problems and additional cost all of which are associated
with self-pitching linked guide vanes.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines in Use
The OE Buoy, Cork
The OE Buoy, developed by OceanEnergy in Cork, is an
offshore device which operates using the OWC principal.
The buoy was developed over a number of model phases,
phase 1 being a 1:50 scale model tested in the wave tank
at the Hydraulics and Maritime Research Centre (HMRC),
University College Cork.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
Self-Rectifying Turbines in Use
The OE Buoy, Cork
The OE Buoy is a Backward Bend Duct Buoy (BBDB) and
uses a Wells turbine in the power conversion unit.
See: https://www.youtube.com/watch?v=GSOFV3f39Ng
https://www.youtube.com/watch?v=hSHgqTCh42A
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy
9/14/2015
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Worked Example 1.2
Q1. Describe some of the variations of Wells turbine
design used in wave power conversion applications and
discuss their advantages/disadvantages
Q2. Compare and contrast the performance of Wells and
Impulse type turbines as used in wave power conversion.
Dr Andrew Cashman MECH7008 Ocean and Hydro Energy