At the beginning of the 21st century, about 80 percent of the energy supply was obtained from fossil fuels. Fossil fuels are finite resources, so most estimates suggest that the proven reserves of oil are enough to satisfy global demand until the middle of the 21st century. So there is a necessity to find an alternative energy resource.
A renewable resource is a resource which is replaced naturally and can be used again. Renewable resources are much cleaner, more reliable and safe. Examples are: oxygen, fresh water, solar energy, timber, biomass, wave energy