Ocean waves are both clean and renewable sources of energy with a tremendous worldwide potential of generating electricity. If fully exploited, about 40% of the world’s power demand could be supplied by this resource – equivalent to as much as 800 nuclear power plants.
What is Wave Energy?
Some of the kinetic (motional) energy in the wind is transformed into waves once the wind hits the ocean surface. Wind energy ultimately forms due to solar energy and its influence on high and low pressure. This is the reason why wave as well as wind power are considered renewable energy sources.
The density of the energy that is transported under the waves under the ocean surface is about five times higher compared to the wind energy 20 meter (about 65 feet) above. In other words, the amount of energy in a single wave is very high.
How Does Wave Power Work?
In 2001, more than 1000 different methods of utilization of wave energy had been patented by many different wave energy companies, most of which never even made it past the first few stages. Only a few of these projects have been shown to work in reality. The following are the three main methods that look most promising:
Oscillating Water Column (OWC)
An oscillating water column is partially lowered into water. It is open below the surface line with a hollow upper part filled with air. The water level within the water column increases and decreases with waves coming in resulting in compression and decompression of air. Wells-turbines are ideal for the purpose of converting this into energy, because the turbines rotate the same way independent of the direction of the airflow. A generator converts this mechanical energy into useful electricity.
Surface-following attenuator (Line Absorber)
The point absorber consists of a series of long unit, floating on the surface of the water following the movements of the wave. It is this movement that is harnessed and converted to electricity in the point absorber.
A Scottish company, Pelamis Wave Power (previously known as Ocean Power Delivery), has installed a successful 2.5 MW wave farm Aguçadoura of the coast of Portugal. This wave power plant was opened in September 2008. Below is a picture of one of the Pelamis Wave Energy Converters that is the foundation of Aguçadoura, maybe the most promising device to harness wave energy so far.
This device looks like a sea snake in the water. It consists of a series of joints that generate power as the waves move them up and down through hydraulic rams and a generator. An underwater cable moves the electricity to the shore.
Buoyancy Unit/Point Absorber
The buoyancy unit is floating on the waves or below the water surface, fixed to the bottom, following the vertical movements of the waves up and down. These waves drive a pump that generates electricity.
The power generation of a typical ocean wave energy unit is about 1 MW, but we expect this output to get better along with the wave energy technology.
After several years with low activity around marine energy technologies, the need for renewable energy has pushed the interest for these technologies forward. Some countries have invested more than others when it comes to developing these methods. Britain and Portugal are currently the leading nations when it comes to ocean wave energy conversion, but several other countries are starting to grasp the potential of harnessing wave energy as well.