Ethanol As A Fuel
Ethanol can be produced from plant material so is known as a biofuel. It's made by fermentation of plants and is used to power cars in some places. It's often mixed with petrol to make better fuel.
Pros: The CO2 released when it's burnt was taken in as the plant grew, so it's known as 'carbon neutral'. The only other product is water.
Cons: Engines need to be converted before they'll work with ethanol fuels. And ethanol fuel isn't widely available. There are worries that farmers will stop growing crops and instead growing crops to make ethanol- this will increase food prices.
Biodiesel as Fuel
Biodiesel is another type of biofuel. It can be produced from vegetable oils such as rapeseed oil and soybean oil. Biodiesel can be mixed with ordinary diesel fuel and used to run a diesel engine.
PROS: Biodiesel is 'carbon neutral'. Engines don't need to be converted. It produces much less sulfur dioxide and 'particulates' than ordinary diesel or petrol.
CONS: We can't make enough to completely replace diesel. It's expensive to make. It could increase food prices like using more ethanol could.
Hydrogen Gas As A Fuel
Hydrogen gas can be used to power vehicles. You get the hydrogen from the electrolysis of water- there's water like everywhere but it takes electrical energy to split it up. This energy can come from renewable sources e.g. solar.
PROS: Hydrogen combines with oxygen in the air to form just water- so it's very clean.
CONS: You need a special, expensive engine and hydrogen is not widely available. You still need to use energy from another source to make it. Also, hydrogen is hard to store.