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Are they the answer to our problems?
by Andreas Swenson
Table of content
Introduction , Purpose and question
Examination
History , Different waves
Facts about wave powerplants
Known problems
Comparing Wave energy with other energy sources
Renewable
Useable areas for exploitation
In the future
Advantages
Disadvantages
Funny facts
Introduction
During the last years the people of the earth has become more and more aware of the destruction of our nature, the
depletion of the resources and the pollution of our environment. The rain forests are cut down, the ozone layer is
broken down and enormous amounts of poisons are emptied out in the seas or directly let free in the atmosphere.
Why is that?
A modern society uses much energy, but where is this energy taken from?
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Today much oil is being imported, that's about 46% of our usage, 16% from nuclear, 14% is waterpower, 8% is
taken from coal, the remainings are biomass, wood, peat etc.
The Government has now decided to liquidate nuclear power and to lower carbon dioxide discharge, but this is
taking a very long time. To be able to solve the energy consumption and to cut down/replace the usage of fossil
fuels, we have to get other sources that are renewable.
70% of our earth is covered with moving oceans, in the oceans a lot of energy is stored as heat and waves. Because
of the large amounts of water it's suitable for energy extractions.
I've chosen to work with wave- and tidal energy because of the availability, and that even small waves can be used
as power source but they whon't give much energy, and because of the exergy efficiency. Tidal energy is almost
identical in the conversion, but tidal is no waves it's just the water level that rises as an influence from the moon,
while the waves is made by the wind blowing on the surface.
Wave energy can be taken from wave breakers, that means, instead of using ordinary wave breakers, you install a
barrage of wave power plants.
Another advantage is that these plants can be used without any noticeable sea life disturbances in the middle of the
ocean.
Purpose and question
Can this work become an inspirer for other people?
The purpose of this work is to inspire people to work with renewable energy sources like wave energy, because of
the high efficiency exchange and it's a natural resource.
I'm interested in this power source of several reasons, it's easy to build, it's non-polluting and I won't to get more
initiated in energy supplies.
Why aren't these power plants being used? They don't pollute the environment, they doesn't affect the nature in high
levels, they can give a high energy exchange as well as exergy exchange, the knowledge to build these plants is easy
to get.
Are there problems? What kinds of problems are there? How can they be solved?
All of these questions are of important, IF they are going to start using these plants, which I hope will be soon.
Examination
History
Trying to tame the waves is not a new idea, hundreds of ideas has been suggested under the last two centuries. One
of the first patents was Girard Messers, Paris from 1799. It was a constructed raft that acts like a buoy, on the raft he
attached a rope that pulled some mechanism.
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However, very few of the ideas were realised before the 1970´s. One of those that were realised was the navigation
buoy, that worked with an hole in the base were he air was pushed up and down by the waves through a whistle,
later they attached a generator for navigation lights. Over 1000 of these buoys are still in action.
Since the energy crisis in the 1970´s, intensive researches have begun in Canada, Japan, USA, India, Portugal,
Norway, Ireland and the UK. They are lead by the International Energy Agency, YEA.
Different waves:
Tides- Tides aren't technically waves, they can be explained like water level rising from the influence on earth from
the moon.
Tsunami- This wave is unusually large (at sea it moves fast, several hundred m/s, when it reaches the shore it raises
up and become high, but it slows down to maybe 100 m/s and 50m- and larger high), it's created when under sea
Vulcan's have eruption or earthquakes.
Tidal wave- Non-technical term for a very large destructive wave.
Facts about wave energy POWER PLANTS
Until now the expenses to wave energy have been larger than to ordinary fuel, the wave devices have withdrawn big
attention as a renewable energy source.
In the next century it's supposed to be a major energy contributor. Many inventions have been tried around the world
as scale models, some of them have even been built in full-scale, here are the full-scale plants located, in England,
Norway, Japan, India, Portugal and USA.
For thousands of years people have known that there is a lot of energy bound to the oceans, unfortunately it's not
very easy to convert this energy to a useable form, such as electricity. The reason for this is that the energy is bound
in slow movements, the wave devices have to change it into a more even power with high frequency.
Now there are several ways to convert the energy in waves, but we are going to talk about the three main wave
converters.
Below:
"The Raft", the water flows up on the inclined plane in to a basin, where it's being lead through a turbine.
When using water the maximum theoretical efficiency is 100%, a lot more than if we were using air that has a
density 8-9 times less than water.
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Below:
The Buoy, an old idea with new improvements, it fills several functions, navigation buoy, with lights and maybe
sound and as a power plant, as a power plant it also provides electricity for the light and stores it in an battery.
The OWC (Oscillating Water Column) works like a piston and pushes the air through the turbine, making it spin.
This power plant can be used as in picture, at sea level and even under water making the water work as a force,
increasing the theoretical efficiency maximum.
One detriment with this type of plant is that the theoretical maximum efficiency is about 60%, when using air as
force.
Below:
Breakwater plant, (can also be used as tidal power plant with some modifications), it work similar to the previous
plant, the air flows through the turbine blades making it spin.
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These plants are designed for coastal defence, land reclamation or harbour wall construction. They can also be fitted
in existing harbour walls.
As before the maximum
theoretical efficiency is about 60% when using air as force.
To understand how much energy there are in the waves, can I say that a wave-line 50 km long contents about 1GW,
in average 15-30 kW/m, depending on the size of the wave.
The number of moving parts in an wave power plant is low, about 25-35%.
Production cost for these devices are rather high (0.60-0.75 SEK)/ kWh, if you compare it to Sweden's waterpower
production cost that are extremely low
(0.10-0.15 SEK) / kWh, but if we compare it with diesel power which have a production cost of 1 SEK / kWh, then
it seems competitive.
Known problems
The main problem is reliability and the costs of the plants.
The demands of today's constructions are:
Durable
Flexible
Cheap
Weather-resistant
Effective- high energy output
The problems lay in, the plant location, salt water tearing on the construction, rust is spread over the plant, brutal
force from heavy waves tearing on the joints.
Comparing Wave energy with other energy sources
If we compare wave energy with other sources of energy we would, with a reasonable wave plant of 1.8 GW in
average production each year, need:
222 tons of coal with all the pollution (1kg coal = 8.1 kWh)
153 tons of raw oil with the same pollution as above (1kg crude oil = 11.7 kWh)
185.567 m 3 natural gas (1 m3 natural gas = 9.7 kWh)
Comparing with air, wave energy is more high quality, because it's theoretically useable up 100%, wind energy is
just useable up to 60%.
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When concerning about energy it should be mentioned that water is 800 times heavier than air and the energy density
is 8 times more than in air.
When comparing nuclear power with wind energy, we can say that nuclear power is very cheap and you can extract
enormous amounts of energy, but there are many detriments with these plants, e.g. radiation for thousands of years,
low exergy output, much heat energy is wasted and if something goes wrong there will be huge environmental
effects.
Renewable
Wave energy is like wind- and water energy, it's a non-polluting renewable energy,
Wave energy will last as long as the sun shines on the earth, temperature differences occur and the wind is blowing.
The only source for renewable energy is from the start, the sun, it's the father to all other renewable energy sources,
and it can also be used directly today, by using solarpanels or solarcells, much work is being done with this
technique, when rays from the sun are directly used to produce electricity, but the sun is also the indirect cause of the
wind, and the wind is causing the waves. Except waterpower plants with large falling heights, the wave energy is
the most powerful source for creating electricity among the renewable sources. The possibilities and the areas are far
larger and doesn't have the same detrimental environmental effects.
The major advantage of wave power compared to other renewable sources is that waves are a natural concentration
of wind energy. Waves are created by the influence of wind energy over a huge area without obstacles, and so
summed and concentrated to a power that can be drained over a very narrow area.
Useable areas for exploitation
Energy can be taken from waves almost everywhere but if the waves are to small expenses will be to high. Below
are the most useable areas for wave energy exploitation marked.
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As above show's, the most wave energy is around the poles, around the equator the water contains less wave
energy, but it's still useful for power extraction.
Tidal power can be used anywhere there is tide, mostly along the coasts.
In the future
Right now wave energy plants only exists in theory models and as experimental rigs, except for maybe five or six
full-scale plants.
But what will happen in the near future?
Tidal and wave energy as a replacement for fossil fuels is uncertain, because the technology of the energy generators
isn't fully developed. In addition the technology isn't fully commercially available making this a relatively expensive
energy choice, remember the enormous cost for a tidal power plant 1.2 billions. Another factor that is standing in the
way for tidal and wave energy, is the growing popularity for other renewable sources, probably will wave and tidal
power be important as alternative renewable source, with today's equipment it's possible to determine the wave
energy devices output two days ahead. Therefore it's possible to make a nice fitting interplay between, wave energy
and the present ordinary, energy type on shore.
Indeed, tidal and wave energy is still a viable option for the future. Although the world's electricity demand could
probably never be met by tidal and wave energy alone, but they have the potential to decrease our reliance on fossil
fuels, for example, in the UK about 20% of the electricity demand could be taken from tidal power.
Worldwide there is a potential of 60 Gigawatts of tidal energy that could be directed to human use. The European
Union has shown great interest in tidal and wave energy and has therefore funded projects in several nations.
You can assume that with increased knowledge and interest in this renewable energy source, costs will decline and
engineering efficiency will improve, with these facts in mind, it seems that tidal and wave energy will encounter a
bright future.
The ABB Alstom Power's future in wave technology lays in their knowledge about turbines, every wave power
plant so far uses some kind of turbine device to extract the power from the waves. So if these wave power plants
would become used in a larger scale, ABB have to be among the first to be a competitive producer.
Advantages
The advantages for using tidal and wave energy over different fossil fuels are plentiful, below there are several
impressive benefits of using tidal and wave energy, including the factor of replacing a percentage of fossil fuel use.
It reduces the dependence upon fossil fuels
Tidal and wave energy is free, renewable, and clean source of energy
Tidal and wave energy consumption creates no liquid or solid pollution
Highly efficient resource ( compared with coal and oil at 30%, tidal power efficiency about 80%)
Energy capturing and conversion mechanism may help protect the shoreline
Energy capturing and conversion mechanism have little visual impact
About 60 billion watts of energy from tides can be used for electricity generation
Tides are active 24 hours a day, 365 days a year
Disadvantages
The disadvantages of using tidal and wave energy must be considered before jumping to conclusion that this
renewable, clean resource is the answer to all our problems.
The main detriment is the cost of those plants, for constructing and running this facility with an annual output of
3423 GWh, is a cost about 1.2 billions, but this doesn't include operational and maintenance cost (coal and oil are
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cheaper).
Despite the fact that it's expensive, you must realise that the technique isn't fully developed. There are still some
uncertainties surrounding the conversion devices.
Construction of strong, cheap and efficient conversion devices may be problematic
Technology isn't fully developed
Problems exist with the transportation of hydroelectricity
Ecological impacts relating to the alteration of tides and waves is not fully understood
Appropriate waves and tides are highly location dependent
Waves are a diffuse energy source, irregular in direction, durability and size
Extreme weather can produce waves of great intensity
Facts:
The World Energy Council estimates that 2TW of energy can be harvested from the waves.
0.1% of all energy would cover the worlds energy consumption five times over.
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