Non renewable energy comes from sources that take a long time to develop and can not be renewed in short time frame. The examples of no renewable energy sources are coal, natural gas, diesel, gasoline, etc. These are also called fossil fuels. They require extraction and processing, both of which require energy from other sources. They generate carbon dioxide and a number of other waste products, all of which need to be cleaned up (again entailing an energy cost- expense of energy to carry out these operations) and hence require a large amount of energy to generate energy. For example, in case of coal, only 29% of the original energy is retained when generating electricity from it. Corresponding values for oil and natural gas are 31% and 38%.
In comparison, renewable energy sources get renewed very quickly and hence are also called non-fossil fuels. Example of renewable energy options include, solar energy, wind energy, geothermal energy, etc. These options do not generate carbon dioxide and many of these do not generate any waste products (think about solar or wind energy, used feed is only sunlight and wind), apart from the manufactured facilities (such as solar cell and wind turbine, past their design life). Hence these are much more efficient than non renewable energy options. For example, wind energy converts as much as 1164% of original energy into electricity.
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