7Ie Photosynthesis and biofuels

Are biofuels carbon neutral?

A carbon neutral fuel is a fuel that does not add any carbon dioxide to the atmosphere when it is burned.

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7Ie Photosynthesis and biofuels

Plants use carbon dioxide from the air in photosynthesis. The material in a plant stores carbon atoms that have been taken out of the atmosphere.

carbon dioxide

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7Ie Photosynthesis and biofuels

Plants can be harvested to be turned into fuel.

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7Ie Photosynthesis and biofuels

Plants must be converted to biofuels such as biodiesel before they can be used as fuel for vehicles. This is done in a refinery.

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7Ie Photosynthesis and biofuels

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The biofuel contains carbon that was originally taken out of the atmosphere by the plants used to make the fuel.

7Ie Photosynthesis and biofuels

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When the biofuel is burned in engines, carbon dioxide is put into the atmosphere.

carbon dioxide

7Ie Photosynthesis and biofuels

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But this carbon dioxide has only recently been taken out of the atmosphere by the plants used to make the fuel. Overall, no carbon dioxide has been added to the atmosphere.

Or has it?

7Ie Photosynthesis and biofuels

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The machinery used to plant the crops and harvest them needed fuel.

Fuel was needed to make fertilisers to help the crops to grow.

The refinery used energy to convert the plants to biofuel.

Unless all these processes also used biofuels, then the biofuel is not really 'carbon neutral'.