Itaipu produces electricity based on hydraulic energy, that is, by developing the gravitational energy potential of the water contained in a raised reservoir. This energy is present in nature and can be developed from pronounced differences in levels or waterfalls.
Before becoming electricity, the energy must be turned into kinetic energy. The device that carries out this transformation is the turbine. A turbine basically consists of a wheel provided with blades, which is made to rotate upon receiving the mass of water. The last element in this chain of transformations is the generator, which converts the rotary movement of the turbine into electricity.
The construction of a hydroelectric power plant in a river entails building a dam to contain it, forming an artificial lake that may undertake two functions: to accumulate water for when there is a reduction in the flow of the river and to provide a difference in levels for the fall of the water (increase in the potential energy).
At Itaipu, the dam serves mainly to produce the difference in levels required for driving the turbines, since its reservoir has a small volume in relation to the river flow (the power plant is of the 'run of the river type').
The dam, however, doesn't completely interrupt the flow of the water. Part of it goes through the power intake, which is the intake structure from which the water will be discharged by the penstocks into the turbines. The remaining water flow rejoins the river bed after going over the spillway, a structure controlled by gates, which are utilized to discharge all the water not employed in the production of energy.
Within the powerhouse, the rotation of the turbine driven by the flow of the water spins the generator rotor, whose magnetic field, upon being displaced, generates electricity.
In absolute terms, the five largest producers of hydroelectricity in the world are Canada, China, Brazil, the United States and Russia. In 2006, these countries were responsible for almost 52,4% of the world's production of electricity (MME - BEN, 2008). Slightly less that 50% of the present hydroelectric capacity installed in Brazil is in the Paraná River Basin. According to the 2008 National Energy Balance, the contribution of hydraulic energy to the national energy grid is around 75%.
Despite the tendency for other sources to increase, due to social-economic and environmental restrictions on hydroelectric projects and the technological advances in the development of other non-conventional sources, everything indicates that hydraulic energy will continue for many years being the main source of the electricity generated in Brazil.
Although the largest remaining potentials are located in regions with strong environmental restrictions and distant from the main consumption centers, it is estimated that in coming years at least 50% of the need to expand the generation capacity will be of hydric origin.