6. Power stations that use renewable energy sources.

Some power stations use clean, renewable energy sources to produce electricity. These alternatives help to reduce our dependence on non-renewable sources of energy, such us fossil fuels, which also cause environmental problems.
Renewable energy sources have been developed and improved in recent years. Although these energy sources give us less electricity than thermal power stations, they have several advantages:

• They are 'greener' than conventional power stations because they produce less pollution.
• They use renewable energy, so they don´t consume limited natural resurces.
• They reduce our dependence on other countries that produce fossil fuels. As a result, we don´t need to import so much fuel.
• They are relatively cheap, in comparison to other energy sources.

6.1. Wind farms.
Wind farms use the kinectic energy of the wind to generate electricity. The wind turns the blades of a turbine, at the top of a tower. The blades are connected to a gearbox, wich increases the rotational speed of the generator.



Wind farms are totally clean source of electricity.
The output and efficiency of a wind farm depend on two factos:

• the location of the farm, which determines the speed and strenght of the winds.
• the number of turbines that can be installed there.

6.2. Hydroelectric power stations.

• Conventional hidrolelectric station.

• Pumped storage hydroelectric stations: the water flows from the turbines to a second reservoir.

6.3. Solar power stations.
Solar power stations use energy from sunlight to generate electricity. There are two main types of solar power station: solar thermal and photovoltaic.

• SOLAR THERMAL STATION.

• PHOTOVOLTAIC STATIONS.

6.4.Biomass power stations.

Biomass is any organic material that is produced by natural processes.

There are many types of biomass which ca be used to produce energy. They include natural vegetation, forestry products and agricultural waste. There are also energy crops, such as sunflowers and beets, which are grown specifically for biomass energy production. Biomass is prepared through various physical and chemical natural processes.

In a biomass power station, the fuel used to produce energy comes from biomass. The steam produced from burning the biomass moves a turbine that is connected to a generator.

6.5. Marine power stations.

Marine power stations use the movement of ocean water to generate electricity. At the moment, most of these stations are experimental. They are very expensive and not very efficient. There are three general types of marine power stations.

• Tidal power stations, which use the energy of tides.
• Wave power station, which use the energy of waves.
• Ocean thermal conversion stations, which use the difference in water temperature between the surface of the ocean and deeper areas to produce energy.

6.6. Geothermal power stations.

Use natural heat from the deepest underground layers of our planet. This heat comes to the Earth's surface as hot water, steam and hot gases.

Geothermal energy can be used in two ways:

• It can be directly to provide hot water for heating and industrial uses.
• It can be used indirectly to drive generators and produce electricity.