A converter is simply a device that alters an input signal from one form to another. Therefore as the name suggests, a wave energy converter is a device that receives the energy harnessed from mainly from ocean or sea waves and uses it to produce electricity. Waves are produced as a result of wind action thus making them an indirect form of solar energy. Large waves exist in the oceans and these remain largely untapped as research in this area can best be defined as being in the formative stage.
Wave energy converters are classified into two main groups namely;

Based on location:

  • These include shoreline converters which are at the coastal shoreline and therefore easy to maintain and less likely to be damaged as they travel through shallow water.
  • Near shore converters are deployed in water which can be defined to be at a depth less than one quarter of a wavelength.
  • Offshore converters are in deep waters and have the advantage of harvesting great amounts of energy although on the flip side, they are more difficult to construct and maintain which increases the cost of their construction.

Based on type

o Attenuators: These lie parallel to the predominant wave direction. A good example of this type is the Pelamis shown in figure 1.

Figure 1: Pelamis wave energy converter

o Terminator converters: These have their main axis parallel to the wave front and hence work by intercepting the waves. The Salter’s Duck, whose mode of operation is explained in Figure 2 is a good example. As the wave hits the device, the water particles cause the duck to rotate thereby transforming not only the kinetic energy of the wave but also the potential energy into mechanical rotation energy.

Figure 2: Salter’s Duck energy converter

o Point absorber converters: These possess small dimensions as compared to the incident wavelength. They can be floating and heaving up and down on the water surface or submerged in the water and thereby relying on the difference in pressure. For these converters, the wave direction is not very important. A good example is Powerbuoy wave converter shown in Figure 3.

Figure 3: Powerbuoy wave converter

Importance of wave energy converters

With an increased demand for power to run the numerous existing and upcoming industries and societies, there is every reason to look further than the existing power supplies which mainly include hydroelectric power, geothermal power, wind and solar, as these are not sufficient. Wave energy is still relatively untapped and therefore provide an enormous opportunity to try and tackle this shortage hence making it a worthwhile area for development.

Background information

Although the possibility of harnessing energy from waves has been around for a long time, it was not until the oil crisis in 1973 that modern research in this area really took off. This technology does not replace other aforementioned power generation methods but offers another alternative, therefore playing a supportive role.

Advantages of wave energy conversion

  • Waves offer a renewable source of energy and therefore have a huge potential for application.
  • Wave power devices have the ability to generate power up to 90% of the time which compares favorably to the 20-30% achieved by wind and solar devices.
  • Sea waves have the highest energy density as compared to other renewable energy sources i.e. wind and solar.
  • Low negative environmental impact.
  • Reduces the over reliance to fossil fuels which has led to adverse effects including emission of greenhouse gasses.

Building a wave energy converter

In order to build a wave energy converter, it is important to first understand the principle on which it works. According to the physical law of conversation of energy, any energy harvesting device must have a wave interaction in such a way as to reduce the amount of energy present in the sea. The converter generates a wave which then interferes destructively with the sea waves.
The components of a wave converter differ depending on the type and mode of operation of the converter. It is safe to conclude that generally, building a commercial wave energy converter requires a lot of time and money. However, it is possible to build a simple point absorbing wave energy converter by making use of a float, a magnet, a coil, a housing, a copper wire and a suction cup. The schematic set up is as shown in Figure 4. To create the coil, a magnetic wire which is enamel coated is wound around a test tube ensuring that there are at least 100 coils. At both ends of the coil, a couple of feet of the wire should be left free so as to allow for connection to a voltmeter. The float is made to move up and down under the influence of the waves thereby causing the connected magnet to also move up and down the coil, producing electricity. The suction cup at the bottom of the water surface ensures that the converter is attached to the bottom of the water body which in our case is a makeshift wave tank. A tank with a capacity of around 100 liters should be enough. The copper wire ends are connected to a voltmeter which can be used to measure the energy output of the converter.
Since this is only a prototype measuring approximately less than 30 cm in length including the mooring, the amount of electricity produced may not be enough to power a simple machine. However, the signal can be analyzed, amplified and used to perform a simple task like lighting a bulb. This setup can also act as a basis for further developments.

Figure 4: Schematic diagram of a point absorbing wave energy converter

References/ Important links
1. Veritas, D. N. (2005). Guidelines on design and operation of wave energy converters. Carbon Trust.
2. Drew, B., Plummer, A. R., & Sahinkaya, M. N. (2009). A review of wave energy converter technology. Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 223(8), 887-902.
3. http://nnmrec.oregonstate.edu/education/build-wave-energy-device

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