Renewable energy technologies are important for sustainable energy because they contribute to world energy security. This reduces our dependence on fossil fuels.  The International Energy Agency states that:“Conceptually, one can define three generations of renewable technologies, reaching back more than 100 years”.

First-generation technologies emerged from the industrial revolution at the end of the 19th century and also include hydropower, biomass combustion, and geothermal power and heat. Some of these technologies are still used even today.Second-generation technologies include solar heating and cooling and wind power. Up to date forms of bioenergy and solar photovoltaic are now entering the mainstream prompted by research, development and demonstration in the 1980s.  This initial research arose out of the environmental concerns due to the oil crises of 1973 and 1979. 

Third-generation technologies are still under development and include advanced “biomass gasification”, “bio refinery” methods and concentrating on “solar thermal power”, “hot dry rock geothermal energy” and wave and tidal power.First- and second-generation technologies are now established but third-generation technologies are still heavily dependent on long term research and development commitments involving the public sector.