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alternative energy-energy derived from sources that do not use up natural resources or harm the environment. energy, free energy - (physics) a thermodynamic quantity equivalent to the capacity of a physical system to do work; the units of energy are joules or ergs; energy can take a wide variety of forms.
Primary energy. Primary energy (PE) is an energy form found in nature that has not been subjected to any human engineered conversion or transformation process. It is energy contained in raw fuels, and other forms of energy received as input to a system. Primary energy can be non-renewable or renewable.