What is the most important characteristic of a good fuel?

"$A$ biogas plant solves the fuel as well as environmental problems". Discuss.

What are the limitations in obtaining energy from wind?

There are about $50$ teachers in a school and most of them come to school by their own cars. Many of the teachers come from the same place but everyone prefers to come to school by his/her own car.
Answer the following questions based on the above information:
$(a)$ Do you think that their practice of commuting to school is environmental-friendly? Give one suggestion. Justify your answer.
$(b)$ In what other two ways can we become environmental-friendly?

Which of the following sources of energy is different from the other?

What type of energy is utilized by a sailing boat?