Two types of energy can be formed in the ocean: heat from the sun known as thermal energy and from waves and tides referred to as mechanical energy. Considering that water covers about 70% of the earth’s surface, it is an enticing thought that the world can be power-driven by only a ration of the heat trapped by the sea. Generally, waves are formed when wind blows consistently on the surface of a large water body whereas tides are formed depending on the gravitational pull of the moon. According to Rutan (2008), the amount of energy produced is directly proportional to wave power. Some of the wave-power rich areas in the world are northern Canada, Australia, southern Africa, Scotland and the northern western coast of the United States. Waves and tides (mechanical energy) provide intermittent source of energy as compared to thermal energy which is fairly constant. Researchers have verified that ocean energy can be a reliable source of energy.
Thermal energy produced by the ocean is used in generation of electricity by conversion systems namely: closed-cycle, open-cycle and hybrid cycle. In closed-cycle system, the warm ocean water evaporates a fluid with a low boiling point which results to vapor expansion thereby turning the turbine. The turbine rotates and fuels the generator to produce power. Open-cycle systems operate at low pressures so as to heat the ocean water (Rutan, 2008). This yields steam to be used in turning the turbines. The hybrid cycle incorporates both the open and closed cycles.
It is important that wave-power devices are to be installed appropriately in order to achieve maximum harnessing of energy. These devices are normally to be installed near shore, offshore or far offshore depending on the operation. Examples of wave technologies are terminator devices, oscillating column, point absorbers, overtopping devices and attenuators (Devine-Wright, 2012). The mostly used wave technology is the point absorber; this device is usually fully or partially submerged in the water. Its size depends on the size of the generation unit, location and depth of the water and also the method being used to extract wave energy. As the name suggests, it absorbs energy from all directions.
Rutan (2008) alleges that in Scotland, The Pelamis Wave Energy Converter has effectively been used to produce energy on the large scale. This equipment operates at 2-10 km offshore and utilizes wave motion to generate power. Water depths of 50 meters and above are suitable for its optimal performance. It floats semi-submerged as it faces the direction of waves. It is built with five tube/cylindrical tubes hinged, therefore, permitting for movement. When waves pass the equipment, it turns making the motion to be opposed by the tubes which then push the liquid into the accelerators at a fast rate raising the pressure. Hydraulic power systems convert the absorbed energy into electricity. The machines transport this produced power to the shore, experiencing some losses during this process.
Pros and cons
Wave and ocean energy has pros and cons. To start with pros, this kind of energy is renewable and is clean. According to Linscott (2011), the waves and tides are very predictable making it easy to harness it and with proper planning substantial amount of energy can be created. Moreover, there are very little pollution and greenhouse gas emissions, therefore, reducing chances of global warming. To the cons, equipment for harnessing are quite costly, size of waves and tides differs from time to time which means that at times when they are very small one may not be in a position to generate power. Most importantly, studies have shown that harnessing wave power may lead to slowing the rotation speed of the earth.
Environmental impact assessment
Environmental impact assessment should be performed before the setting up of a wave energy plant, and several factors are to be considered (Melnyk, & Andersen, 2009). The effects, both negative and positive, on the marine habitat; if there are any toxic substances to be released in the water; how to handle any spills or leaks; noise caused by the machine; and if there are other users in the sea already such as recreational boating, to avoid conflicts.