TEXT FOR ADDITIONAL READING AND UNDERSTANDING
Other sources of energy
Other power stations use the energy from wave or tidal motion , wind, sunlight or the energy of falling water, hydroelectricity. These types of energy sources are called renewable energy.
Hydroelectricity
Hydroelectric dams impound a reservoir of water and release it through one or more water turbines to generate electricity.
Pumped storage
A pumped storage hydroelectric power plant is a net consumer of energy but decreases the price of electricity. Water is pumped to a high reservoir when the demand, and price, for electricity is low. During hours of peak demand, when the price of electricity is high, the stored water is released through turbines to produce electric power.
Solar
A solar photovoltaic power plant uses photovoltaic cells to convert sunlight into direct current electricity using the photoelectric effect. This type of plant does not use rotating machines for energy conversion.
Solar thermal power plants are another type of solar power plant. They use either parabolic troughs or heliostats to direct sunlight onto a pipe containing a heat transfer fluid, such as oil. The heated oil is then used to boil water into steam, which turns a turbine that drives an electrical generator. The central tower type of solar thermal power plant uses hundreds or thousands of mirrors, depending on size, to direct sunlight onto a receiver on top of a tower. Again, the heat is used to produce steam to turn turbines that drive electrical generators.
There is yet another type of solar thermal electric plant. The sunlight strikes the bottom of a water pond, warming the lowest layer of water which is prevented from rising by a salt gradient. A Rankine cycle engine exploits the temperature difference in the water layers to produce electricity.
Not many solar thermal electric plants have been built. Most of them can be found in the Mojave Desert of the United States although Sandia National Laboratory (again in the United States), Israel and Spain have also built a few plants.
Wind
Wind turbines can be used to generate electricity in areas with strong, steady winds, sometimes offshore. Many different designs have been used in the past, but almost all modern turbines being produced today use a three-bladed, upwind design. Grid-connected wind turbines now being built are much larger than the units installed during the 1970s, and so produce power more cheaply and reliably than earlier models. With larger turbines (on the order of one megawatt), the blades move more slowly than older, smaller, units, which makes them less visually distracting and safer for airborne animals. Old turbines are still used at some wind farms.