Wave Energy Converter Seminar 2011 1. INTRODUCTION Today more than 80 per cent of the world’s electric power production comes from fossil- fuelled plants. As the demand for electricity is forecasted to increase, there is an urgent need to find new methods to extract electric energy from renewable sources. Renewable electric energy supply is today one of the highest priorities in many parts of the world. The Kyoto declaration 1997 and the last agreement at Marrakech 2002 are significant proofof this. Both the EU and the US have set their targets on future greenhouse emissions. Ocean waves represent a vast unexplored source of renewable energy. The wave energy potential in the EU has been estimated conservati vely as 120– 190 TWh/yea r offsh ore and an additional 34–46 TWh/year at near shore locations. However, these estimations depend on assumptions of technology and energy cost. The actual resource could be a magnitude larger. In any case, it will be a challenging task to convert the vast energies in the ocean waves into electric energy. When approaching sustainable electric power production for the future, attention must be paid to the economical constraints. The social, ecological and environmental impacts also need to be addressed. The need forresearch and investigations in this area must not be underestimated. Today, several countries have national efforts within wave energy. The dominating countries in the development of wave power have so far been Denmark, India, Ireland, Japan, Norway, Portugal, The Netherlands, Australia, UK and USA. The Swedish waters have been estimated to contain too little wave energy and the general opinion has been that it could not be motivated to do research on small 5–50 kW conversion devices. From the mid eighties the area has been considered difficult and uneconomical. Despite this, one of the more tested technologies has been developed in Sweden, the so-called IPS OWEC Buoy with a power of 100 kW or more. It is now further developed in the USA and UK. The device is pumping water up and down, thereby driving a traditional generator. The ocean wave’s behaviors have been the objectives for many investigations. However, apart from some tests, mechanical solutions with a traditional rotating generatorVVIT EEE Dept1
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Today more than 80 per cent of the world’s electric power production comes from fossil-
fuelled plants. As the demand for electricity is forecasted to increase, there is an urgent need
to find new methods to extract electric energy from renewable sources. Renewable electric
energy supply is today one of the highest priorities in many parts of the world.
The Kyoto declaration 1997 and the last agreement at Marrakech 2002 are significant proof
of this. Both the EU and the US have set their targets on future greenhouse emissions. Ocean
waves represent a vast unexplored source of renewable energy. The wave energy potential inthe EU has been estimated conservatively as 120–190 TWh/year offshore and an additional
34–46 TWh/year at near shore locations.
However, these estimations depend on assumptions of technology and energy cost. The actual
resource could be a magnitude larger. In any case, it will be a challenging task to convert the
vast energies in the ocean waves into electric energy. When approaching sustainable electric
power production for the future, attention must be paid to the economical constraints.
The social, ecological and environmental impacts also need to be addressed. The need for
research and investigations in this area must not be underestimated.
Today, several countries have national efforts within wave energy. The dominating countries
in the development of wave power have so far been Denmark, India, Ireland, Japan, Norway,
Portugal, The Netherlands, Australia, UK and USA.
The Swedish waters have been estimated to contain too little wave energy and the general
opinion has been that it could not be motivated to do research on small 5–50 kW conversion
devices. From the mid eighties the area has been considered difficult and uneconomical.
Despite this, one of the more tested technologies has been developed in Sweden, the so-called
IPS OWEC Buoy with a power of 100 kW or more. It is now further developed in the USA
and UK. The device is pumping water up and down, thereby driving a traditional generator.
The ocean wave’s behaviors have been the objectives for many investigations. However,
apart from some tests, mechanical solutions with a traditional rotating generator
Fig 2.An individual wave energy converter under deployment
2.1.1. MACHINE CONFIGURATION
General description
A possible WEC concept with a linear generator as power take-off is shown in Figure (1).
The WEC consists of a buoy coupled directly to the rotor of a linear generator by a rope. The
tension of the rope is maintained with a spring pulling the rotor downwards. The rotor will
move up and down at approximately the same speed as the waves and the maximum speed
will be in the order of 1 m/s. The relatively low speed implies that the reaction force
developed between the rotor and stator to be very high. For example, a 10 kW generator
needs a reaction force in the order of 10 KN with a rotor speed of 1 m/s. This implies that adirectly driven generator must be larger than a conventional high-speed generator.
Stator
The stator is made of laminated electrical steel, piled into one solid unit, The conductors are
power cables with a circular cross-section and a conducting area of 16 mm2, insulated with a
1.1 mm PVC-layer, which adds up to an outer diameter of 7.2 mm. The coil winding is a
three-phase winding with a slot per pole and phase ratio of 5/4. This winding configuration
aims at minimizing the fluctuation in the output power caused by cogging. A three-phase
AC. An optional shore transformer could also include a tap changer in order to compensate
voltage variations,
• Another option, similar to the first, is to move the converter offshore which limits land use.
However, this increases the complexity and may decrease the availability as maintenance will
be more weather dependent. The converter can be placed on a platform or enclosed in a
watertight container on the seabed.
• A further development would be to also install a transformer offshore. This would increase
power transmission possibilities since power is proportional to the square of the voltage, i.e.
for the same power rating the current is lower with higher transmission voltage.• A fourth option includes a high voltage DC “HVDC” transmission link. This implies a
higher degree of complexity, but transmission losses are kept at a minimum. However, the
power components losses will be added. A platform or watertight enclosure is also required
for the electrical power components.
2.1.3. POINT ABSORBER ARRAYS
Shadowing effects
Theoretically, up to 50% of the incoming wave energy can be absorbed by a system of
oscillating point absorbers, i.e. an array of buoys [8]. For
Individual buoys absorption of 20% of the incoming energy has been observed [5]. In a
simplified model, neglecting three-dimensional scattering of waves, buoys at the back of an
array will receive less energy than those at the front for a wave field with a predominant
direction. If the absorption over the width of the buoy is assumed to be 20%, and the spacing
is ten times the buoy diameter, only 2% of the incoming energy will be
Absorbed by each row. For the n: th row in an array subjected to unidirectional waves the
available power flux will be attenuated by 0.98n-1. In this way, for an ideal wave climate
with sinusoidal waves from one direction a 20-row-array will receive at least 83% of the
incoming power flux. For a rectangular shape of the array, the effects of
buoy “shadowing” will depend on the prevailing wave direction. To improve this situation,
the buoys could be arranged in a hexagonal pattern, forming a
and it will open when the floating air column on crest. One valve is to the low-pressure fluid
pipe and it will open when the floating air column on the trough. The whole system is
anchored to the sea bottom.
2.2.1. COMPONENTS
a). The huge mass floating body: - It can be made of iron or concrete (or water or sand
can be used for the huge mass).
b) The pipe systems for the hydraulic fluid: The pipe system is wired through inside of the
floating body.
c) Piston shafts, Pistons and cylinders: - Made of cast iron.
d). Bottom side open floating air columns: - Can be made of anticorrosive- long lastingmaterial like PVC etc. [The floating air columns made of a number of small units of
floating systems will be more secure instead of a large single floating column].
e) Air tight fluid tank: - This tank is partially filled with fluid and air. This tank takes an
important role as the fluid collector when overflow from the cylinders and supplier in the
shortage of the fluid in the cylinders.
f). The anchors: - The anchor is used to keep the floating system on position.
g). Power transmission: - The power can be transmitted to the grid through the under
ground (under water) cables.
2.2.2. WORKING
When the wave moves through the floating air columns, it to oscillate the floating air
columns. When some of the air columns (air columns that on the crest) move upward, the
whole weight of the floating system will be supported through that air columns. Also,
now some floating air columns (the air columns that on the trough) will move downward.
As some of the air columns move upward, the pistons of those air columns to pressurize
its corresponding cylinders and the hydraulic fluid inside of the cylinders rush to the high-
pressure fluid pipe with high pressure (now the valves to the low-pressure fluid pipe will
be closed). Since the whole of the high-pressure fluid pipes are interconnected, the net