Our country, Korea, has specified energy sources other than oil, coal, nuclear power and natural gas and sorted them into 11 fields to be used in the future (Alternative Energy Development & Promotion of Use and Distribution Act).
They have been classified as follows;

* 8 fields for renewable energy sources
  - Solar energy, Photovoltaic power, Biomass, Wind power, Small hydro power,
    Geothermal energy, Ocean energy and Waste energy.
* 3 fields for new energy sources
  - Fuel cell, Coal liquefaction/gasification, Hydrogen energy.

Alternative energy sources that have been put to practical use as a result of extensive technology development carried out by developed countries today are mostly solar and wind energy. The development of other alternative energy sources such as biomass, geothermal energy, wave energy and tide energy has been actively carried out.

Future energy sources that can provide sustainable energy.

Developed countries around the world have been carried out extensive research and development for alternative energy and shaped policies on supply, since alternative energy is the most effective solution of the depletion of fossil fuels and environmental crisis, despite the excessive initial investments needed.
The significance of alternative energy has recently been recognized, as people feel insecure with unstable oil price and restriction set by the United Nations Framework Convention on Climate Change.
The development of alternative energy should be considered as a prime issue from the viewpoint of environment, traffic and national security, along with the fact that the energy supply system has quickly changed from central supply system to locally dispersed system nowadays.