Dams
Dams are structures built of inorganic material that is spread across a river or a body of water. (Childess, 2008) In doing so, water is collected behind the dam and the potential energy of these water builds up. A tunnel is built high up on the walls of the dam to drain water downwards onto the power house of the dam, where the turbines and generators are located. When the fast flowing water flows through the turbines, the turbine spins due to the kinetic energy exerted onto it and electrical energy is subsequently generated.
Hydroelectric Energy
Hydroelectricity extracts energy from the energy stored in moving water through a number of ways. There is the conventional way that involves dams being built over rivers or turbines built underwater that captures tidal energy. Roughly 16% of the world’s electricity are produced through Hydropower with China being the largest producers of Hydropower through Dams. (Wish, 2011) Other types of Hydroelectricity could include Tidal energy.
Video showing how a dam works. Reproduced from http://www.youtube.com/watch?v=rnPEtwQtmGQ
Advantages
Clean
Energy generated from dams create almost negligible amounts of air pollution as compared to energy from the burning of coal or fossil fuels. Hence it is a sustainable method of energy production.
Security
The energy is stored as potential energy in the water reserves, hence there is energy security as there is a large reserve of water kept behind the dam which can be released into the power house to generate electricity when needed.
Disadvantages
Land Change
When the dam is constructed, a large amount of water is held back behind the dam. The resultant is a waterlogged plot of land being created, and the extent of the damage depends on the geography and amount of water being held back. In unfortunate cases, huge communities of flora and fauna could be destroyed by the flooding. A good example would be the case of the Three Gorges Dam in China where it destroyed a large area of habitat required for the endangered Giant Pandas. As seen from the image on the right, a large area of vegetation was waterlogged after the construction of the dam.
Environmental Changes
Sediments and minerals are also trapped behind the dams when it is constructed. Fast flowing water is required to efficiently carry heavier sediments or minerals along the river. When dams are constructed, the speed of the water is greatly reduced, thus sediments and minerals sink to the bottom of the water body behind the dam. As a result, the water that are released through the dams are greatly filtered. Such poses problems for the habitats that are present further down the river as they will lack the essential minerals needed for survival. It is estimated that almost 1,100 cubic kilometres of sediments were accumulated behind the all the worlds dam in 1986 alone. (McCully, 1996)
Before and after image of the area surrounding the Three Gorges Dam,China. Reproduced from
Effects of dams on a river. Reproduced from http://www.vtwaterquality.org/wqd_mgtplan/swms_appC.htm
Tidal Energy
Tidal energy converts the power of the tides into electricity. Tidal stream generator is the conventional type of tidal generating methods. It uses the kinetic energy in tides to generate energy. The concept is somewhat similar to how wind energy powers wind turbines. The tides will move through the turbines and the underwater turbines will be powered by the kinetic energy of the tides.
Brief summary of tidal electricity. Reproduced from
Advantages
Predictable
Tidal energy is very predictable. Once the proper research and experiments are done and the figures of how much electricity one particular area can generate, the figures will be consistent. (Anne, 2013) Such would lead to energy security for that particular area as disruption of energy would be unlikely due to the predictable nature of tidal energy.
Renewable
Tidal energy is renewable and thus, would not be depleted. Tides are caused by the gravitational effects of the sun and the moon on earth. Thus, as long as those two exist we would be able to harness tidal energy.
Clean
Tidal energy produces zero amounts of green house gases nor byproducts that are hazardous to the enviroment. Therefore, it is a clean and sustainable way of obtaining energy.
Disadvantages
Environmental Concern
The turbines installed on ocean beds could have serious environmental effects. The process of installing the turbines could destroy marine lift on sea beds. The presence of the turbine could possibly hinder the movements of larger marine animals and affect the migration movements of fishes
Disruption to shipping routes
Once tidal turbines are installed on the seabed, large ships will no longer be able to move through that particular area due to the obstruction present. As such, the contruction of tidal turbines can disrupt and deny transportation through sea.