What is the main source of energy for the earth?

State the energy transformation in the following —

1. electricity is obtained from solar energy.
2. electricity is obtained from wind energy.
3. electricity is obtained from hydro energy.
4. electricity is obtained from nuclear energy.

Name the two groups in which various sources of energy are classified. State on what basis are they classified.

What is meant by renewable and non-renewable sources of energy? State two differences between them, giving two examples of each.