What are the two characteristics of a good source of energy?

The basic characteristics of a good source of energy are as follows:

1. The source of energy should not cause any kind of environmental pollution.

2. The source of energy should produce a great amount of energy per unit mass or volume.

3. It should not cause any kind of harm to people and should not be risky to the health of people handling it.

4. The source of energy should be easily available and should have the capacity to generate energy for maximum amount of time.