The present and possible future replacements for fossil fuels have been described in Chapters 4, 5, 6 and 7. The biofuels can be solid, gaseous and liquid as follows:

Solid:

• Biomass.

• Waste materials.

Gaseous:

• Methane.

• Hydrogen.

• Dimethyl ether (DME).

Liquid:

• Methanol.

• Ethanol.

• Biobutanol.

• Synthetic Fischer-Tropsch (FT) petrol.

• Biodiesel.

• Bio-oil.

• Synthetic FT diesel.

• Microalgal biodiesel.

Solid fuel replacements

As described in Chapter 4, biomass in the form of wood, specific energy crops, crop residues and organic wastes can be used to replace coal and natural gas. Biomass can be burnt, co-fired with coal and gasified to generate electricity and heat. Small- to medium-size heating systems have been developed to use pelleted biomass. The pyrolysis and gasification of biomass can be used to produce a liquid fuel, which can be used for transport, electricity generation and to provide heat.