Which one of the following energy source is not a commercial source?

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Accepted Answer

Biogas. Biogas is produced after organic materials (plant and animal products) are broken down by bacteria in an oxygen free environment, a process called anaerobic digestion or anaerobic fermentation. Biogas systems use anaerobic digestion to recycle these organic materials, turning them into biogas which contains both energy (gas) and valuable soil products (liquids and solids). Anaerobic digestion already occurs in nature, landfills and some livestock manure management systems but can be optimized, controlled and contained using an anaerobic digester. Biogas contains roughly 50-70 percent methane, 30-40 percent carbon dioxide and trace amounts of other gases. Biogas is not a commercial source. It is mainly used for domestic purpose.

Which one of the following energy source is not a commercial source?

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