Electricity from the Ocean Waves
This durability and resilience are key reasons why silicone films can be used in what is known as energy harvesting. Silicone-Based Electroactive Polymers for Energy Generation is a joint research project in which a consortium of four industrial companies and two universities under the direction of Robert Bosch GmbH is working to develop wave power generators. In this context, researchers at Darmstadt Technical University created a preliminary model of a wave power plant resembling a buoy: whose upper half floats on the surface of the water while its lower half is anchored to the sea floor. The two halves are joined together by a stack of thousands of conductively coated silicone films which change shape at intervals of three to ten seconds in response to the motion of the waves. A positively charged electrode is mounted above the highly insulating silicone, and a negatively charged electrode below it. The action of the waves first compresses the silicone and then relaxes it again. As the water level rises and falls, the two electrodes above and below the silicone elastomer move toward one another and then apart. As soon as the silicone film has relaxed and recovered its thickness, the two electrodes, and therefore their charges, move apart - and the electrical energy in the converter is increased. This produces the desired outcome of converting the mechanical energy from the wave into electrical energy. “The electrical currents in the individual layers are cumulative,” explains Dr. Istvan Denes of Central Research at Bosch, who heads the project.
Silicone elastomers are rubber-elastic materials consisting of inorganic polysiloxanes that crosslink irreversibly to yield a three-dimensional network. Silicone elastomers have a property profile that makes them indispensable in many industrial applications: extraordinary heat resistance, low-temperature flexibility, chemical inertness and biocompatibility. These materials have a strongly hydrophobic, i.e. water-repellent, surface, are selectively permeable to gases, and are very good electrical insulators. A typical characteristic is their high resistance to a large number of physical and chemical influences, which is why, unlike organic rubber compounds, they do not age. Thus, their chemical, physical and technical properties remain virtually constant over the temperature range of roughly -45 to +200 degrees Celsius. Silicone elastomers can cope with constant mechanical and electrical loads as well as continuous exposure to oxygen, ozone and UV radiation.
Multiple converters generate electricity in an array. The efficiency of the pilot plant in Darmstadt was determined to be around 50 percent, which is higher than that of conventional power plants. The first reduced-to-scale model of this kind of wave power generator will now be launched in the wave flume at Hamburg-Harburg Technical University.
Generators based on silicone films do not require hydraulic parts or turbines, making them virtually maintenance free and hence significantly cheaper to operate than conventional wave power plants with their fragile, hydraulic moving parts. This means that, in the not too distant future, we may well see wave power plants anchored off of our coasts, generating electricity from the ceaseless up-and-down motion of the waves.
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