Physics Project Hydroelectricity

Hydroelectricity

Electricity from Hydropower

Hydropower is considered a renewable energy resource because it uses the Earth’s water cycle to generate electricity. Water evaporates from the Earth’s surface, forms clouds, precipitates back to earth, and flows toward the ocean.

The movement of water as it flows downstream creates kinetic energy that can be converted into electricity. A hydroelectric power plant converts this energy into electricity by forcing water, often held at a dam, through a hydraulic turbine that is connected to a generator. The water exits the turbine and is returned to a stream or riverbed below the dam.

Hydropower is mostly dependent upon precipitation and elevation changes; high precipitation levels and large elevation changes are necessary to generate significant quantities of electricity. Therefore, an area such as the mountainous Pacific Northwest has more productive hydropower plants than an area such as theGulfCoast, which might have large amounts of precipitation but is comparatively flat.

Environmental Impacts

Although hydropower has no air quality impacts, construction and operation of hydropower dams can significantly affect natural river systems as well as fish and wildlife populations. Assessment of the environmental impacts of a specific hydropower facility requires case-by-case review.

Although power plants are regulated by federal and state laws to protect human health and the environment, there is a wide variation of environmental impacts associated with power generation technologies.

The purpose of the following section is to give consumers a better idea of the specific ecological impacts associated with hydropower.

Air Emissions

Hydropower’s air emissions are negligible because no fuels are burned. However, if a large amount of vegetation is growing along the riverbed when a dam is built, it can decay in the lake that is created, causing the build-up and release of methane, a potent greenhouse gas.

Water Resource Use

Hydropower often requires the use of dams, which can greatly affect the flow of rivers, altering ecosystems and affecting the wildlife and people who depend on those waters.

Often, water at the bottom of the lake created by a dam is inhospitable to fish because it is much colder and oxygen-poor compared with water at the top. When this colder, oxygen-poor water is released into the river, it can kill fish living downstream that are accustomed to warmer, oxygen-rich water.

In addition, some dams withhold water and then release it all at once, causing the river downstream to suddenly flood. This action can disrupt plant and wildlife habitats and affect drinking water supplies.

Water Discharges

Hydroelectric power plants release water back into rivers after it passes through turbines. This water is not polluted by the process of creating electricity.

Solid Waste Generation

The use of water to create electricity does not produce a substantial amount of solid waste.

Land Resource Use

The construction of hydropower plants can alter sizable portions of land when dams are constructed and lakes are created, flooding land that may have once served as wildlife habitat, farmland, and scenic retreats. Hydroelectric dams can cause erosion along the riverbed upstream and downstream, which can further disturb wildlife ecosystems and fish populations.

Hydroelectric power plants affect various fish populations in different ways. Most notably, certain salmon populations in the Northwest depend on rivers for their life cycles. These populations have been dramatically reduced by the network of large dams in the ColumbiaRiver Basin.¹ When young salmon travel downstream toward the ocean, they may be killed by turbine blades at hydropower plants. When adult salmon attempt to swim upstream to reproduce, they may not be able to get past the dams. For this reason, some hydroelectric dams now have special side channels or structures to help the fish continue upstream.

Reserves

In the United States, hydropower generates nearly nine percent of the total electricity supply. In the Pacific Northwestalone, hydropower provides about two-thirds of the region’s electricity supply.² Currently, facilities in the U.S. can generate enough hydropower to supply electricity to 28 million households, which is equivalent to about 500 million barrels of oil. In 2003, total hydropower capacity in the United States was 96,000 MW.³ The undeveloped capacity for the United States is approximately 30,000 MW.⁴

1. U.S.Department of Energy, Energy Efficiency and Renewable Energy Network, Hydropower Topics.
2. U.S.Department of Energy, Hydropower Program, Hydropower: Partnership with the Environment
3. Energy Information Administration, Electricity Generating Capacity, 2002-2003.
4. U.S.Department of Energy, Hydropower Program, Undeveloped Hydropower Potential by State.

http://www.epa.gov/cleanenergy/energy-and-you/affect/hydro.html

Conventional Method

The scientific process behind hydroelectric power is very simple, mostly relies on some of the basic laws of physics. There is two levels to the hydroelectric process, first is the water cycle in nature. The second part is more mechanical, a hydroelectric dam capitalizes on gravity by blocks the flow of water from a higher elevation to a lower elevation. The gravitational force of water as it falls from high elevation to low elevation while passes through the dam is utilized by the turbine. As the water falls toward earth, the turbines spin and cause the generator. The physical processes is summed up in several physics equations, first,

F = ma, F=m * (change in velocity / change in time)

Where F is force, m is mass, and a is acceleration. For the process of hydroelectric power, F is the force of the water that is falling toward the earth. The constant “a” stands for acceleration, and is a value that accounts for the change in velocity divided by the change in time.

Pumped-storage

This method produces electricity to supply high peak demands by moving water between reservoirs at different elevations. At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine. Pumped-storage schemes currently provide the most commercially important means of large-scale grid energy storage and improve the daily capacity factor of the generation system.

Pumped storage is a method of keeping water in reserve for peak period power demands by pumping water that has already flowed through the turbines back up a storage pool above the power plant at a time when customer demand for energy is low, such as during the middle of the night. The water is then allowed to flow back through the turbine-generators at times when demand is high and a heavy load is placed on the system.

The reservoir acts much like a battery, storing power in the form of water when demands are low and producing maximum power during daily and seasonal peak periods. An advantage of pumped storage is that hydroelectric generating units are able to start up quickly and make rapid adjustments in output. They operate efficiently when used for one hour or several hours. Because pumped storage reservoirs are relatively small, construction costs are generally low compared with conventional hydropower facilities.

Run-of-the-river

Run-of-the-river hydroelectric stations are those with small or no reservoir capacity, so that the water coming from upstream must be used for generation at that moment, or must be allowed to bypass the dam.

Tide

A tidal power plant makes use of the daily rise and fall of ocean water due to tides; such sources are highly predictable, and if conditions permit construction of reservoirs, can also be dispatchable to generate power during high demand periods. Less common types of hydro schemes use water’s kinetic energy or undammed sources such as undershot waterwheels.

Underground

An underground power station makes use of a large natural height difference between two waterways, such as a waterfall or mountain lake. An underground tunnel is constructed to take water from the high reservoir to the generating hall built in an underground cavern near the lowest point of the water tunnel and a horizontal tailrace taking water away to the lower outlet waterway.

The creation of hydroelectric energy will cause environmental and social implications. It will affect the quality of water by causing an increase of water temperature, which will deplete oxygen supply while gaining phosphorus and nitrogen. The decrease in oxygen and an increase in gases unsuitable for the healthy growth of wildlife will stunt growth and development. The water will also be polluted with clay or silt as siltation occurs. As well, the presence of dams will obstruct aquatic life from their adapted migration patterns. Salmon numbers in theUnited Stateswere declining rapidly where hydroelectric dams were constructed, as they had to make a difficult and dangerous journey downstream while attempting to avoid the turbines. The disruption of the entire ecosystem occurs with the upset of water content, an unbalance of distribution of water, and the destruction of aquatic life habitat.

There are several social implications with the construction and maintenance of hydroelectric projects. Issues can first arise when communities do not accept the creation of dams which can lead to opposition and protests against the project. Worsening the situation is when the public’s voice dealing with the issues of the impact the dams have had on their community goes unrecognized which can deepen the tension between the government or the companies that are building the dams and the community they are disrupting.

A significant issue is the displacement of communities. In order to construct dams, land will be being flooded thereby displacing small towns or villages, sometimes involuntarily. In particular, when minority Aboriginal groups are displaced from their land with which they hold a deep connection to culturally and spiritually, it can have very adverse effects on the community as they have liven on the land their whole lives and has few transferable skills. The community cohesion may crack and self-determination can falter.

Another implication of the construction of hydroelectric dams is the spread of diseases and illnesses that can be found to have further reaching effects downstream than at the immediate site of assembly. The risk of health problems increase for displaced communities and employees working on the dam when the water content is contaminated. This affects the aquatic wildlife and fisheries as bioaccumulation occur.

Socially, the building of the dams requires much manpower, supplies, and capital. This will also provide for more employment however it will also create increased visitation to the area and further disrupt the balance of the environment, especially since the assembly and operation will take place over a long period of time. Reservoirs created by hydroelectric schemes often provide facilities for water sports, and become tourist attractions themselves. In some countries, aquaculture in reservoirs is common. Multi-use dams installed for irrigation support agriculture with a relatively constant water supply. Large hydro dams can control floods, which would otherwise affect people living downstream of the project.

Article byU.S.Environmental Protection Agency. Retrieved June 05, 2011 from

http://www.epa.gov/cleanenergy/energy-and-you/affect/hydro.html

Sources

Hydroelectric Power: How it works, USGS Water Science for Schools. Retrieved June 03, 2011 from

http://ga.water.usgs.gov/edu/hyhowworks.html

WisconsinValley Improvement Company – How Hydropower Works. Retrieved June 03, 2011 from

http://new.wvic.com/index.php?option=com_content&task=view&id=8&Itemid=45

Energy Resources: Hydroelectric power. Retrieved June 03, 2011 from

http://www.darvill.clara.net/altenerg/hydro.htm

Sustainable Hydro Power – Social – Aspect. Retrieved June 03, 2011 from

http://www.sustainablehydropower.org/site/social/populationdisplacement.html

The Physics of Hydro Power. Retrieved June 03, 2011 from

http://library.thinkquest.org/17658/hydro/hydphysicsht.html

Energy Matters: Problems with Hydroelectric Power. Retrieved June 02, 2011 from

http://library.thinkquest.org/20331/types/hydro/problems.html

Hydro power. Retrieved June 02, 2011 from

http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/Hydro%20Power.htm

Project Compiled by
Helen M, Lisa H, and Sajedeh G

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