Energy is the key issue of whether human race and all the other lives can be sustained or not in earth for the future. However, since the green-house effect of the carbon-dioxide in the atmosphere creates the global warming which is not only changing the climate but also destroying the environment of all the creatures on earth needed. The mankind survival is threatened now. Therefore, green energy is suddenly noticed and needed urgently in this decade. in this course, we provide the knowledge of various existing green energy methods and introduce the ideas as well as techniques of how to develop possible new green energy system.