Electricity Generation

Potential energy -> kinetic energy -> hydroelectricity -> mechanical electricity -> electrical energy

//Energy Conversion

The water at the top of the dam contains a large amount of potential energy, providing the opportunity for electricity to be generated. The water flows from the reservoir to the dam and then to the power plant through a large pipe or tube. Water pressure, from the weight of the water and gravity, forces the water through the penstock and onto the blades of a turbine. The moving water then pushes the blades and spins the turbine. The turbine is connected to an electrical generator inside the powerhouse. The generator produces electricity that travels over long-distance power lines to homes and businesses. This entire process is called hydroelectricity.

Hydroelectricity is generated in large power generating stations using the same basic principle as a small grist mill, but on a much larger and improved scale for better efficiency. Electrical generators are attached to massive turbine devices which spin at great speeds as a result of water rushing through them. These massive turbines are extremely efficient at extracting the kinetic energy from moving water and converting that energy into power through these generators. It is the turbine and generator working in combination that converts mechanical energy into electric energy.

//Conditions for electricity generation

However, in order to generate electricity from the kinetic energy in moving water, the water has to be moving with sufficient speed and volume to turn a generator. Roughly speaking, one gallon of water per second falling one hundred feet can generate one kilowatt of electrical power. The water that used in this process is a renewable energy resource, just like the wind that turns the turbine attached to a generator.

The hydroelectricity extracted from water not only depends on the volume and speed, but also on the difference in height between the source and the water’s outflow. This height difference is called the head. The amount of potential energy in water is directly proportional to the head. Therefore, it is advantageous to build power dams as high as possible to convert the maximum energy from mechanical energy.

//Types of Hydroelectricity Generation

Hydroelectric generation can work without dams, in a process known as diversion, or run-of-the-river. Portions of water from fast-flowing rivers, often at or near waterfalls, can be diverted through a penstock to a turbine set in the river or off to the side. An example of diversion hydropower is the generating stations at Niagara Falls. Another run-of-the-river design uses a traditional water wheel on a floating platform to capture the kinetic force of the moving river. While this approach is inexpensive and easy to implement, it doesn't produce much power. For example, if the entire Amazon River is harnessed this way, it would only produce 650 MW of power.

Another type of hydropower, though not a true energy source, is pumped storage. In a pumped storage plant, water is pumped from a lower reservoir to a higher reservoir during off-peak times, using electricity generated from other types of energy sources. When the power is needed, it is released back into the lower reservoir through turbines. Some power will be lost, but pumped storage systems can be up to 80 percent efficient. There is currently more than 90 GW of pumped storage capacity worldwide, with about one-quarter of that in the United States. Future increases in pumped storage capacity could result from the integration of hydropower and wind power technologies. Researchers believe that hydropower may be able to act as a battery for wind power by storing water during high wind periods.