In physics, energy is power derived from physycal or chemical resources to provide light and heat or to work machines.
Renewable energy is energy which comes from naural resources and are naturally replenished.
A tipical renewable fuel is ethanol producted by a biological way, through the glucose fermentation of some strains of yeast. Renewable energy resources comes from all natural elements around us: Sun, wind, oceans, rivers and plants. Unlike fossil fuels, they won't run out and don't pollute the environment.
Solar technologies use the Sun's energy to provide heat, light, hot water, electricity. Electricity may be obtained by using photovoltaic pannels made out of silicon, phosphorus and boron. When the rays of Sun hit the pannels, the combination of theese material produces energy.
Another way to produce "green energy" is represented by water cinetic strenght. Hydropower is energy resulted from falling water to drive turbines. It can use be harnessed for several kind of purposes, such as the irrigation or the operations of varius mechanical devices. Today, hydropower is mainly used to produce electric energy by the rotation of turbines.
In a wind-powered electricity generating system, the wind turns the blades of a windmill, the motion of the blades makes a turbine rotate and electricity is generated.
Many countries have very long costlines and so can consider using the water in the oceans as an energy resource. Wave energy conversion enables the energy in waves to be used to generate electrical energy and tidal power generation uses the natural motion of the tide to make energy.
A geothermal energy resource uses heat from within the Earth. Wells drilled into the soil bring the hot water or steam on the surface. It is also possible to use the hot water to heat houses directly.