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in the circuit. The hydraulic liquid can only be looked on as a part of the transmission, because liquid cannot be compressed and used for storing of energy. Some have the pumping system beneath the surface and some over the surface. A converter of the latest type is WaveStar. Currently it is being tested in the Limfjord. Two parallel rows of nearly half spherical floats on arms are transmitting the movements from the waves by hydraulic pumps to a hydraulic turbine. This converter shows that it is possible to have many floats close to each other, without loosing much to the shadow affect. Behind a single float the waves are recovering very quickly by attraction of energy from the surroundings. It is a function according to the principle of Huyghens. An interesting combination of wind power and float-based wave converter is the Poseidons Organ. The floats are placed on a row like keys on an organ. This plant is floating by itself and has ordinary wind turbines on the top. Poseidons Organ is probably the next to be tested in a bigger scale. 4 Offshore Center Denmark Newsletter ON/OFF 10 - May 2007 Another special type of float-based converter is the Wave Plunger, where the waves cause the float to run up and down on a slant tower. A group of float-based converters consist of chains of pontoons, formed as plane flaps or cylindrical containers. The power take off is most commonly by hydraulic pumps on the top or inside the pontoons, when the limbs in the chain are shifting angular position to each other, caused by the waves. The last type of float-based converters to be mentioned this time is the WaveSpinner, an invention of Povlonis Innovation. The transmission from the float is mechanical and causes directly rotation of a couple of flywheels and a generator. The principle has been tested and shown to work in a small scale and is now waiting for investments to be built in a bigger scale. Another promising type of converters is the Wave Rotors. The first Dane, who got his wave energy converter patented, was the engineer Tage Basse. He invented a rotor with fish fin like blades, which surprisingly rotated horizontally in the water Offshore Wind Power Basic Course The course will provide insight into the common occurring technologies encountered in the offshore wind industry. Topics include: Turbine technology, foundations, environment, service and maintenance etc. May 30+31 2007 in Herning Read more and register at: www.offshorecenter.dk surface. Later was shown that a Darrieus rotor, known from wind technology, also works in water waves. A combination has now been built and is going to be tested in open sea. Povl-Otto Nissen concludes: “As you see there are a lot of possibilities for exploiting wave energy. None of the ongoing experiments have so far shown to be the ultimate answer to how to do it best. The special Danish grass-root method of improving new ideas worked well for the wind power section. We are trying to do it in this area too. But experimenting with wave energy is much more demanding and expensive compared to putting up some wings and a generator on a pole in your backyard. It is not easy without some sort of financial support right from the beginning. But it is of great fun.” WaveSpinner Povl-Otto Nissen explains the ideas behind his own wave energy converter, the WaveSpinner: “At first the possibility of collecting energy from waves had to be demonstrated more convincing. It was done by inventing a wave hoist and making a model out of every day things. The float was two joined beer cans. The transmission system was an asymmetric rocker arm on a tower, all made of construction iron band. When the movements of the float caused the rocker arm to tilt, a piece of bent fence wire turned a tooth wheel, which was connected to horizontal barrel. A weight on a string was then winded up on the barrel step by step. The barrel was prevented to run backward by another piece of bent fence wire. It worked. The construction can be used as a wave hoist on oil rigs, if they have the patience to wait for it. Next step was to organise the power take off. In stead of the string a bicycle chain was used. The weight to be lifted was tied to
the chain and lifted wave by wave to the top and over it. When falling down on the other side it turned two bicycle generators, just fast enough to get a small flash of light in a couple of bulbs. Next step again was to overcome the time gaps between the incoming wave crests to get a continued rotation. What about the principle of an old time foot driven sewing machine? Yes, but it has a fixed crank system, which is not suited for power input from a great variety of wave heights and different wave periods. How could that be solved? Take a look at the pictures and guess. The up and down movements of the float are transformed to a continued rotation of at couple of flywheels. It is double working. The volume and weight of the float can be optimised to deliver energy to the flywheel system twice every wave period. According to the law of Archemedes it is a question of interaction between gravity and the lift on the float. A PM-generator will be integrated in the flywheel system. (pat.nr. DK200100543, publ.date: 2003-1-20) So far a module in scale 1 to 20 has been built and tested with promising results. Next step is to build a bigger model in non corrosive materials to demonstrate survival in the very tough environments. After that it should be easy to combine many modules to a big wave electric power plant. The WaveSpinner could be placed on its own legs or in the combination with breakwaters. It could be hanging under bridges or on oil platforms. The modules could also be placed on submerged pontoons, connected with a horizontal plate to give stability and resistance.” Povlonis Innovation is quite a young company dealing with research, development and mediation Povl-Otto Nissen concludes: “We are convinced that wave power plants, contrary to what you often see, should consist of small relatively light weight but strong units, and then connected and combined to bigger plants. We are heading to demonstrate the feasibility of one module at first, somewhere in the North Sea, where 90% of the energy is available up to 3.5 meter wave heights and wave periods between 2 and 7 seconds. If someone in charge would find that interesting, let us talk about it.”n The manager, Povl-Otto Nissen, has been experimenting with wave energy since 1995. He is a physicist of education, has been headmaster of a Danish Folk High School, associate professor at Ribe College of Education, since year 2000 engaged in establishing the Poul la Cour Museum in Askov, Denmark. He is also the author of the biography of two scientists: “Poul la Cour og vindmøllerne” and “Röntgen og de mystiske stråler”, published by Polyteknisk Forlag. Offshore Center Denmark 5 Newsletter ON/OFF 10 - May 2007
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Page 7 and 8: The story about Wave Star Energy Wa
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Page 11 and 12: The expected lifetime of the demons
Page 13 and 14: Design of Access Platforms for Offs
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