Primary energy sources can be classified in to two groups: nonrenewable and renewable. Secondary sources are derived from primary sources.
Energy that comes from a source that’s constantly renewed, such as the sun and wind, it can be replenished naturally in a short period of time.
Energy that is converted from primary sources are secondary sources of energy. Secondary sources of energy are used to store, move and deliver energy in an easily usable form. Examples include electricity and hydrogen.