Non-conventional energy sources are those energy sources, that are -

Non-conventional energy sources, also known as renewable energy sources, are those that are naturally replenished and are virtually inexhaustible over a human time scale. These include solar energy, wind energy, tidal energy, geothermal energy, and biomass.

• Renewable: Unlike conventional sources (coal, petroleum, natural gas), non-conventional sources do not deplete with use and generally have a significantly lower environmental impact.
• Conventional sources: These are traditional, finite resources that are non-renewable and contribute to environmental pollution.

Because non-conventional sources are derived from ongoing natural processes, they are classified as renewable energy.