New non-fossil fuel based energy sources has become an important technological need for the next years. This technology won’t only fuel economic growth and contribute to global environmental sustainability, but also reduce the energy dependence on oil. The predominant renewable energy sources include but not limited to ocean wave energy, wind energy, biofuels and solar energy.
Ocean waves possess huge amounts of kinetic energy of motion that goes almost entirely untapped. Ocean waves can provide 15-20 times more available energy per square meter than either wind or solar.
A wave energy converter (WEC) includes a mechanism for absorbing wave energy and converting it into linear or rotary motion, and another mechanism for converting this motion into a more useful and convenient type of energy which is usually electrical energy.
So far, the available mechanisms for converting linear or rotary motion (mechanical energy) into electrical energy typically contain a magnet and coil and operate based on magnetic induction principals. These mechanical systems are large, high cost and expensive to maintain. An example of such devices is the APB-350 buoy from Ocean Power Technologies, Inc. This buoy weighs 10 tons and produces 300 watts of continuous electric power.
Electric energy production using piezo electric material has been explored extensively. However, a majority of this research considers low power applications. The piezoelectric material is formed into small cantilever beams, the dimensions of which can range from several micrometers to few millimeters. The vibrations of this cantilever beam cause the piezoelectric material to undergo cyclic tension and compression and thus a voltage is produced across its sides. The produced voltage is in the order of few millivolts. Typical application of such devices includes distributed sensor networks in which the vibration type cantilever generators provide a low-cost, maintenance free and reliable source of energy.
The application of piezoelectric materials as a means of converting ocean wave energy to electrical energy has also been explored, however in these applications, the same cantilever beam mechanism or the PVDF films have been used and the power generated is low which make them suitable for off shore low power sensor systems.
The key idea in the presented WEC device is that the maximum energy should be absorbed by the system when a wave passes through it. High voltage piezoelectric generation has the following advantages over low voltage generation:
1- The presented WEC absorbs more energy from the passing wave which increases the efficiency
2- The high voltage generated is AC by nature which eliminates the need for DC to AC conversion circuits.
3- The generated high voltage which is in the order of kilovolts can be transmitted over a long distance without any considerable loss and thus eliminates the need for step-up transformers in the transmission line.
4- The storage medium which could be battery packs, capacitor bank or super capacitors can be installed on-shore which reduces the weight of the system.
5- The presented WEC is simple, low cost, low maintenance and easy to manufacture.