Introduction to Wave Energy

As stated in an earlier post, wave energy is one of the two renewable energy sources which belong to the Ocean subcategory of the more general hydro energy renewable sources. Wave energy is the energy carried by the waves on the surface of the ocean or sea, which can be captured and be used for the production of electricity, water desalination and other useful activities. It must be stated that there is tremendous energy in waves and thus this form of energy cannot be neglected.

In order for us to be able to capture wave energy, we need waves.

How are the waves produced?

Waves are produced by wind blowing over the oceans. The wave duration, height, speed, the energy it contains and many other parameters differ from region to region and ocean to ocean. In many regions the wind blows consistently, in strength and duration, and this make wave energy predictable and thus more exploitable and marketable.

There are two basic ways we can trap wave energy using different wave power devices. The first way is trapping the wave energy at the surface of the wave from essentially the surface motion of the waves and the second way is the pressure fluctuations caused below the surface of the waves.

One important factor that one should have in mind is that wave energy is different than tidal energy and the two forms of energy should not be confused. The energy a wave carries is directly proportional to the square of its height and thus the waves generated in oceans are definitely stronger and carry more energy than the ones generated in usually calm seas, like the Mediterranean Sea.

One may very well ask the question,

Why Wave Energy?

There various reasons why we consider tapping wave energy and using it as an alternative renewable green energy. Some of these are:

• It is clean, renewable and environmentally friendly
• Waves are available to a lot of countries thus making wave energy a widely distributed renewable from of energy
• Once waves are generated they travel great distances with little loss of energy
• Through the use of satellites, waves are anticipated 1-2 days  in advance, thus they are predictable and this enable electricity network operators to plan and manage usage
• Waves have a good seasonality and their existence coincides with the high demand seasons of various regions of the world
• Waves are usually out of phase with their generating source, the wind, and given the fact that they travel great distances, the two energy sources can be used to complement each other.

Wave Technologies:

There are various forms of wave technologies that have been developed recently and/or improved recently so as to capture the power of the waves in the most efficient way.  First of all, we have to note that wave capturing devices can be installed at one of the following 3 locations:  nearshore, offshore and far offshore. Choosing the right technology and the right type of location is done under a careful techno-economic evaluation.  We have identified 4 different types of wave energy capturing devices that even though all of them are installed at the surface or near the surface of the ocean they differ in the way they interact with the waves, capture the wave energy and the way they convert this energy into electricity. These 4 technologies are:

• Terminator devices: these devices are installed to extend perpendicular to the way the wave travels and capture the wave energy by ‘’reflection’’.  These devices started as nearshore devices but their recent developments have enabled them to be installed offshore and sometimes far offshore.
• Point absorbers: Point absorbers are floating structures that are installed on the surface of the sea and move with the wave motion and relative to each other. This relative motion is converted into energy through the use of electromechanical or hydraulic energy converters.
• Attenuators: These are long floating structures installed parallel to the direction of the wave, the different height of the waves causes them to be flexed and this drives hydraulic energy converters and thus captures the wave energy.
• Overtopping devices:  These devices are essentially reservoirs that get full with the waves and when the water is emptied, the power due to gravity drives hydro turbines the same way as the hydroelectricity is produced.

Environmental Implications:

There are some environmental issues in the case of wave energy that may need to be addressed. These are issues with possible pollution from the technologies used and the disturbance of the sea life in the vicinity of these technologies. Any wave energy project needs to address these issues and handle them adequately.

Wave energy is a renewable green energy that has a lot to give to mankind and we believe that it is still at the stage of infancy. Wave energy technologies need to mature and become more cost effective is wave energy is to be fully exploited and we believe that wave energy has a lot to offer.