A form of energy might take more energy to harness than it provides because of dissipated energy. During the transformation process, not all of the energy will be converted to useful energy. Some of the energy are dissipated in the form of heat. Renewable resources are resources that are replenished at a faster rate than they are used. They become non-renewable when these resources are used up at a faster rate than they are replenished. We don't use renewable resources for everything that we use energy for because the energy transformation might be inefficient or requires a lot of capital and maintenance.
Nuclear fission is the process of splitting apart nuclei. When nuclei fission energy is released. So much energy is released that there is a measurable decrease in mass, from the mass-energy equivalence. This means that some of the mass is converted to energy.
