5 energy sources used as alternative?

Answer 1

The answer depends on how to define alternative energy sources.
Alternative energy sources may be typically and interchangeably for renewable energy sources.

If this is the case then the five energy sources used as alternative are:

• Solar,
• Wind,
• Biomass,
• wave, and
  
• Tidal alternate energy sources
  

Alternative energy sources may be defined as sources of usable energy intended to replace fuel sources without undesired consequences of replaced fuels Typically excluding fossil fuels and nuclear energy). If this is the case then the five energy sources used as alternative are:

• Coal as alternative to wood,
• Petroleum as alternative to whale oil,
• Alcohol as alternative to fossil fuel,
• Coal gasification as alternative to expensive petroleum, and
• Renewable energy as alternative to nonrenewable energy.
  

For more details it may be referred to:
http:/en.wikipedia.org/wiki/Alternative_energy