|Fig. 1: Hydroelectric Cycle (Source: Wikimedia Commons)|
With the persistent threat of global warming it is vital to reduce mankind's dependence on fossil fuels, and find renewable sources cable of providing efficient and clean energy. Although nuclear energy, geothermal energy, solar power, and wind power each act as valuable alternatives to fossil fuels, hydropower is the world's largest source of renewable, emission-free electricity.  Since 1970 hydropower output has more than doubled, and it accounted for sixteen percent of the world's renewable electricity output in 2011 with a capacity of 950 GWs.  The United States, however, does not lead the world in hydropower capacity. Instead China currently stands as the foremost user of hydropower in the world. 
Hydropower takes advantage of gravity and the force that flowing water creates to capture energy. As shown in Fig. 1, dams are the primary structures necessary for high-scaled hydropower plants, and are usually built on large rivers with elevation plunges. The purpose of the dam is to raise the level of the river, create falling water, and control the flows of water. The dam creates a reservoir behind it that is able to store energy by containing water. As the water falls through the floodgate inside the dam it spins a turbine. The turbine is connected to a generator, which in turn takes the mechanical energy from the turbine and converts it to electrical power. Transmission lines connected to the generator then carry the electricity to different places for it to be used.
Hydropower in the United States currently exists as the largest source of emissions-free electricity. It also accounts for roughly over six percent of the total electricity output in in the United States, and 63 percent of the total power from renewable resources in America.  Under the Federal Energy Regulatory Commission there are close to 2,300 hydroelectric dams in the United States, the largest being the Grand Coulee Dam along the Columbia River in Washington State. Its total electricity output amounts to 21 billion KWh every year. 
Most notably, the main advantage of hydropower like other forms of alternative energy lays in the fact that it does not require highly contaminating carbon-emissions. Pollution results from hydropower only during the initial construction of the dam. Furthermore, hydroelectric dams have long lifespans between 50 to 100 years.  They are thus stable and worthy long-term investments, and can be upgraded with modern technologies. With regard to economics, river water does not experience the same market fluctuations as fuel or natural gas because it is a domestic resource. The average generation cost of electricity from hydropower plants in the United States is between USD 50 to 100 per megawatt-hour, making it competitive with nuclear energy and natural gas.  Unlike costly fossil fuels, hydropower plants have relatively low operating and maintenance costs usually between USD 5 to 20 per megawatt-hour. 
Regardless of the clean energy that hydropower creates there are definite environmental and economic consequences that must be considered. The initial fixed costs for constructing a dam for hydroelectricity are significant, and can amount to 2 to 4 million US dollars per megawatt.  Dams have also directly impacted the well-being of animals and plants along the rivers on which they lay. The prime example is in the Klamath River were the construction of dams has led to eutrophication, warmer water temperatures, and altered migration courses. 
Although there are definite environmental consequences to using hydropower, it saves the United States 200 million metric tons of carbon emissions each year.  Furthermore, the low maintenance and operation costs of hydropower plants outweigh their expensive fixed costs. Future technologies will only improve existing dams, and increase the potential for hydropower not only in the United States but also throughout world. For all the aforementioned reasons and given its high efficiency and stability nations cable of producing hydroelectricity should strongly consider investing in hydropower technologies and projects.
© Alejandro Rosenkranz. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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