Physics

8.7 - Biofuels

7 min

What biofuels are

Benefits of biofuels

Problems with biofuels

note 1 of 3

Biofuels

Biofuels are renewable energy resources made from plant materials or animal waste, such as specially grown crops, fast-growing trees, farm waste, animal droppings and landfill rubbish.
They are renewable because crops can be regrown and waste is continually produced at the same rate they're consumed.
They can be solid, liquid or gas, and are burnt to release their stored chemical energy.
They are used to:
- Generate electricity in power stations (driving a turbine and generator).
- Fuel vehicles, replacing petrol or diesel.

Arrows from five labelled circles - animal droppings, landfill rubbish, farm waste, fast-growing trees and specially grown crops - point inwards to green barrels with flames, labelled biofuels.

note 2 of 3

Are biofuels carbon neutral?

Biofuels are often described as carbon neutral because the overall change in atmospheric carbon dioxide (CO₂) from using them is claimed to be zero:

Plants absorb CO₂ from the atmosphere during photosynthesis as they grow.
When the biofuel is burnt, that same amount of CO₂ is released back into the atmosphere.

A grey circle labelled C with an arrow down to a leafy potted plant, an arrow from the plant to a burning flask of green liquid, and an arrow up to another C.

Why the claim is debated

In practice, biofuels are rarely completely carbon neutral:
- Fossil fuels are burnt by machinery during the growing, harvesting, transporting and refining processes, releasing extra CO₂.
- Forests are sometimes cleared to grow biofuel crops, which releases stored carbon and destroys habitats.
Despite this, biofuels still have a significantly lower carbon footprint than fossil fuels.

note 3 of 3

Advantages and disadvantages of biofuels

Advantages	Disadvantages
Reliable - crops grow relatively quickly and can provide a steady, continuous fuel supply.	High cost of refining and processing biofuels.
Can be stored - fuels can be stockpiled to respond to changes in demand.	Fuel crops take up land and water needed for food production.
Renewable and produce less net CO₂ than fossil fuels.	Deforestation to clear land for crops destroys habitats and releases CO₂ and methane.

key terms

TermDefinition

BiofuelA renewable energy resource made from plant materials or animal waste.

Carbon neutralA process that has no overall effect on the amount of carbon dioxide in the atmosphere.

end of notes

Key points to remember

Biofuels

Biofuels are renewable energy resources made from plant materials or animal waste, such as specially grown crops, fast-growing trees, farm waste, animal droppings and landfill rubbish.

They are renewable because crops can be regrown and waste is continually produced at the same rate they're consumed.

They can be solid, liquid or gas, and are burnt to release their stored chemical energy.

They are used to:

Generate electricity in power stations (driving a turbine and generator).
Fuel vehicles, replacing petrol or diesel.

Are biofuels carbon neutral?

Biofuels are often described as carbon neutral because the overall change in atmospheric carbon dioxide (CO₂) from using them is claimed to be zero:

Plants absorb CO₂ from the atmosphere during photosynthesis as they grow.

When the biofuel is burnt, that same amount of CO₂ is released back into the atmosphere.

Advantages and disadvantages of biofuels

Advantages	Disadvantages
Reliable - crops grow relatively quickly and can provide a steady, continuous fuel supply.	High cost of refining and processing biofuels.
Can be stored - fuels can be stockpiled to respond to changes in demand.	Fuel crops take up land and water needed for food production.
Renewable and produce less net CO₂ than fossil fuels.	Deforestation to clear land for crops destroys habitats and releases CO₂ and methane.