large hydroelectric systems

Large scale hydroelectric plants have long been a reliable means of generating renewable energy.  For those countries with plentiful water resources it is the primary method of generating electricity.  Overall, about 20% of the world's electricity comes from hydroelectric sources.  Canada, with its abundant streams and rivers gets 70% of its electricity from hydroelectric plants. The U.S. only gets about 6.6% of its electric power from hydroelectric facilities. 

History of Hydroelectricity in the U.S.

Soon after the discovery of electric generators in the mid 1800's businesses quickly adapted themselves to leverage this new source of energy.  The logical place to begin was with locations which were already leveraging hydrodynamics, mills with water wheels. One of the first mills to convert water wheels to hydroelectric was the Wolverine Chair Factory in Grand Rapids, Michigan in 1880.  It used its turbine to light sixteen brush-arc lamps in the factory.  That was soon followed by a hydroelectric plant on the Fox River in Appleton, Wisconsin in 1882.

Initially the turbines were put in place to power the mills themselves and the factories that they ran.  Sometime excess electricity was sold to the public.  However, as the demand for electricity from the public grew hydroelectric mills targeting public consumption came into being.  The first commercial hydro-station for the transmission of public power was built in 1891 at Telluride, Colorado.  In 1895 a large scale facility was built to harness the power from Niagara Falls.  By 1907 hydroelectric power accounted for about 15% of all electricity in the U.S. 

The demand for electricity continued to grow rapidly throughout the early 20th century as cities industrialized and added electric lighting, electric trolleys and electric appliances.  The initial suite of mill conversion hydroelectric plants gave way to large-scale hydroelectric plants.  The government became a major player in these efforts with projects such as the Tennessee Valley Authority and Hoover Dam.  The use of hydroelectric peaked at about 40% of U.S. electric production by around 1940. 

Following World War II nuclear plants entered the energy arena and became yet another source for electric production and many hydroelectric projects were cancelled.  Because of the oil shortage in the late 70's there was a brief resurgence of hydroelectric with the National Energy Act of 1978 which had been strongly supported by President Jimmy Carter. But overall hydroelectric declined in the U.S. to its current level of about 6.6%.  However, in other parts of the world many new large-scale hydroelectric projects have been launched.  Many of these have been in Asia as that part of the world has begun to industrialize.  The largest by far is the Three Gorges Dam project in China which created a reservoir for over 400 miles.

How Large Hydroelectric Plants Work

Large hydroelectric plants use the stored kinetic energy of water in lakes, reservoirs and rivers to drive large water turbines.  The structures of these plants are fairly straightforward.  On the reservoir side of the dam there is an intake valve or area which feeds water to the turbine.  Usually the intake area has a series of screens to filter out dirt and sediment so these materials do not damage the turbine.   The water flows through a shaft referred to as penstock which channels the water to the turbine.  The blades of the turbine are positioned so as to take optimal advantage of the energy of the water flowing through the penstock.  Once the water has passed through the turbine blades the water is then released into a stream or river. 

How a Large Turbine Works

Hydroelectric turbines in hydroelectric plants work on the same principles as the generator you have in your automobile, electric induction.  Whenever wires are moved through a magnetic field an electric current is produced. In a large hydroelectric generator the power of falling water is used to turn the wire assembly called a rotor.

The structure of the generator can be seen below. At the center of the generator there is a large metal shaft. At the bottom end of the shaft are a series of blades, sort of like a giant propeller.  The water from the dam is directed into those blades through a group of slots called wicket gates.  The wicket gates are designed so that the greatest amount of water will strike the turbine blades without creating too much turbulence.  At the top end of the generator shaft is the rotor assembly which is a series of wire coils.  As the shaft turns the wires through a magnetic field an electrical current is created.

Pros and Cons of Large Hydro

Hydroelectricity is a renewable energy that generates no pollution and no hydrocarbons.  Though most dams are subject to some degree of silt buildup, for the most part, once built they can provide decades of pollution free energy generation.  However, large scale hydro does have some detractors.  Hydro plants can disrupt fish migration in rivers.  Moreover, man made reservoirs can displace both wildlife and people and cause significant environmental disruption.  However, this disruption needs to be balanced against the benefits provided.  For example, many dam projects such as those that make up the Tennessee Valley Authority have not only provided electricity, but have helped prevent flooding which would have caused extensive damage to farms and homes as well as loss of life.  On balance, in an era where global warming threatens our planet, hydro power, both large-scale and small-scale appear to be an excellent power generation option.