Comparison of electricity production methods: hydroelectric and geothermal sources

Hydroelectric vs. Geothermal Electricity Production

In a world that is becoming ever-increasingly focused on the production of energy and fuel, the methods of hydroelectric electricity production and geothermal electricity production have become topics in which the public is significantly interested. In beginning to understand the future of each of these types of electricity production, one must first understand the basic definition of each, as well as the basis for their implementation into the world market. In understanding how each mode of electricity production works, one can begin comparing and contrasting the two in order to understand which modes of production are best utilized in certain situations, as well as to understand the future prospects of each form of production.

Hydroelectric Electricity

Hydroelectricity is the term referring to electricity generated by hydropower, which is the production of electrical power through the use of the gravitational force of falling or flowing water, which is the most widely used form of renewable energy (Wade, p. 653). As hydro means "water," and hydropower means "water power," hydroelectric power is electricity generated using strictly water power (CEC, p.1). Such a method for harnessing power has been utilized throughout history, using water power to help them with their work, and in recent decades, the move to harnessing water power in order to produce electricity has been significant. Hydropower harnesses water power to create reliable, clean and plentiful renewable energy (DOE: Hydropower, p. 1). Once a hydroelectric complex is constructed, the project yields no direct waste, and has a considerably lower output level of the greenhouse gas carbon dioxide than fossil-fuel-powered energy plants (Tenner, p. 92).

Hydroelectric power is largely processed in five different ways: conventionally, through pumped-storage, with run-of-the-river stations, tide stations, and underground stations. These processing standards are generally divided into two different distinctions: those having the capacity to process power for large geographical areas, and those that do not. In viewing the two facets of production that are most commonly used and have the ability to create electricity for vast areas -- conventional and pumped-storage -- one can better understand the process by which power is generated. Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator, and the power extracted from the water depends on the volume and on the difference in height between the source and the water's overflow (Nature, p. 420). Such power is created in conventional stations, otherwise referred to as dams. With pumped-storage hydroelectricity, electricity is produced by moving water between reservoirs at different elevations, with times of low electrical demand yielding to the pumping of water into the higher reservoir (Brennan, p. 3). When there is higher demand, water is released back into the lower reservoir through a turbine, and in this manner, pumped-storage systems currently provide the most commercially important means of large-scale grid energy storage and improve the daily capacity factor of the generation system (Blakeway, p. 218).

The following three production stations generally service smaller geographical areas, but utilize the same basic components that make hydropower so efficient. Run-of-the-river hydroelectric stations are those with little to no reservoir capacity, and these stations are built in a manner that allows water coming from upstream to be used for generation at that moment, or be allowed to bypass the dam entirely, allowing such stations to power generally smaller locations. Similar to the aforementioned power station, tidal power plants are generally only able to cater to a small geographical location, utilizing the daily rise and fall of ocean water due to tides to generate power. Finally, with an underground power station, the facility makes use of large natural height differences found between two waterways that occur in nature. Such facilities are generally found near features such as a waterfall or mountain lake, and are constructed with an underground tunnel that takes water from the high reservoir to the generating hall built in an underground cavern near the lowers point of the water tunnel and a horizontal tailrace taking water away to the lower outlet waterway (Graham, p. 52).

Geothermal Electricity

Geothermal electricity, on the other hand, is electricity generated from geothermal energy found within the Earth. The word "geothermal" comes from the Greek words geo -- meaning Earth -- and therme -- meaning heat -- so, geothermal energy is essentially heat generated within the Earth, which can be recovered as steam or hot water for use in generating electricity (USEIC, p.1). The basic principle in geothermal heating and cooling is that heat is being moved from one place to another through a ground source heat pump that works in much the same way as a refrigerator or air conditioner, by simply moving air either away from where there is too much or to an area in which there is too little (Asheville, p. 1). Geothermal energy is defined as heat from the Earth, which is a clean, renewable resource that provides significant energy within the United States and around the world in a variety of different applications and resources (GEA, p.1).

Geothermal electricity, much like hydroelectric power is produced within its own distinct set of stations that are able to harness the heat from the Earth's core in a manner that is used to create power that can then be distributed to different areas of use. These stations include dry steam power plants, flash steam power plants, and binary cycle power plants, and while each operated on the same capacity to harness heat from the Earth to generate power, each maintains its own set of distinct operating standards and characteristics.

Dry steam power plants are the simplest and oldest design, using direct geothermal steam of 150°C or greater to turn turbines (IGA, p.1). Flash steam power plants operate in a manner that pull deep, high-pressure hot water into lower-pressure tanks and use the resulting flashed steam to drive turbines -- requiring fluid temperatures of at least 180°C (DOE: Geothermal, p.1). Flash steam power plants are the most common type of geothermal plant in operation today (DOE: Geothermal, p.1). Finally, binary cycle power plants, which are the world's most recent development in geothermal energy, can accept fluid temperatures as low as 57°C to drive turbines (Benoit, Blackwell and Holdman, p.566). This moderately hot geothermal water is passed by a secondary fluid with a much lower boiling point than water, which causes the secondary fluid to flash vaporize, driving the turbines (Benoit, Blackwell and Holdman, p.565). This is the most common type of geothermal electricity plant being constructed today, as the thermal efficiency of the plant is about 10-13% (OEERE, p.1).

Similarities, Differences, and Future Utilization

As seen in viewing the aforementioned definitions of each type of electricity, each respective area is its own complicated and individual process. However, while the differences between hydroelectric electricity and geothermal electricity are vast and complicated, dealing with not only the sources from which each draws its own power but the methods of producing the power and making it accessible for public use, is similarities are more basic. The most distinct similarity between hydroelectric electricity and geothermal electricity is their pure source and respective prospect for environmental sustainability, that make each source of power a contender in viewing the future landscape of energy production and distribution around the world.