Hydropower is the most developed of all renewable energy technologies. Ten-percent of our nation's (20% of the world's) electricity demand is supplied by hydropower. That is enough electricity to supply 28 million households, or the equivalent of one-half billion barrels of oil. If this power was produced by coal-fired generating stations, 7.7 million tons of particulates and 296 million tons of carbon dioxide would be added to the atmosphere annually. Yet hydropower is being generated at only 3% of our nation's 80,000 dams. The Federal Energy Regulatory Commission (FERC) estimates that hydropower generation could be more than doubled by modifying existing dams. Worldwide, hydropower supplies 24% of electricity demand, enough for about one billion people. The Grand Coulee Dam (on the right) on the Columbia River in Washington is the largest hydroelectric facility in the United States (Photo courtsey of the US Bureau of Reclamation).

Simply stated, hydroelectric plants convert the energy in moving water(kinetic) into electrical energy. The energy in the water spins a turbine and the trubine then turns a generator which produces electricity. A simple diagram of the overall process is found on the Tennessee Valley Authority's website. You can take a virtual step-by-step tour through a hydroelectric project on the Foundation for Water and Education website.

The amount of energy produced depends on the volume and speed of water flowing and the vertical distance between the turbines and the water surface (head). These two factors determine whether a dam can be an economical source of power. Of these, the most limiting is water flow. The stream to be dammed must have an average annual water flow sufficient to support hydropower. This restricts large hydro projects in arid and semi-arid regions, and is the reason one does not find large hydro projects in Kansas.

There are basically three types of hydropower generation plants. Low-head (<30 meters) development or Run-of-river plants tap the energy in streams and rivers. These plants sometimes use small reservoirs retaining up to a week's water supply, but low speed turbines are used which are designed to handle large volumes of water at low pressure, so often, no reservoir is needed. Run-of-river plants are small units and subject to large fluctuations in output due to variable rainfall. Bowersock is a 2.5 MW run-of-the-river facility on the Kaw (Kansas) River in Lawrence.

Medium-head (30 meters - 300 meters) development storage plants consist of a large dam in a mountainous area which creates a huge reservoir. The Grand Coulee Dam on the Columbia River in Washington (108 meters high, 1270 meters wide, 9450 MW) and the Hoover Dam on the Colorado River in Arizona/Nevada (220 meters high, 380 meters wide, 2000 MW) are good examples. These dams are true engineering marvels. In fact, the American Society of Civil Engineers as designated Hoover Dam as one of the seven civil engineering wonders of the modern world, but the massive lakes created by these dams are a graphic example of our ability to manipulate the environment - for better or worse. Dams are also used for flood control, irrigation, recreation, and often are the main source of potable water for many communities. Hydroelectric development is also possible in areas such as Niagra Falls where natural elevation changes can be used.

Another type of medium-head facility is a pumped storage plant. Most generators can also be used as motors, and in a pumped storage plant, power is generated by water flowing from the reservoir through the dam when it is needed, and when excess power is available, the turbine generators are used as motors to pump water back into the reservoir. This arrangement may seem odd, but it makes economic sense. For example, suppose that a particular area whose electricity demand varies from 100 MW to 150 MW. It is less expensive to install 125 MW of base-power (coal, nuclear) and a peak-power plant (hydro) which can deliver or absorb 25 MW than it is to install 100 MW of base power and 50 MW of peak power.

In the final type of hydropower facility, high-head developments, there must be an elevation difference of at least 300 meters between the turbines and the water surface. Generating stations of this type are found in the Alps and other mountainous areas, and high-speed turbines are used.