The bio-fuels, wood and grass and peat, were the original fuels for fire to heat and cook by, but they could not be grown at the rate at which they were being used, which eventually led to the undermining and extinction of several civilizations.
The same is happening with fossil fuels now, and although bio-fuels are a way of reducing CO2 emissions, there will never be sufficient bio-fuels to replace the use of fossil fuels as the current of usage.
However whilst we use significant amounts of biological materials for other purposes, there is a waste stream from their consumption, which can usefully be used as bio-fuels to add to energy from other ambient heat producing resources.
Bio-fuels are manufactured from a diverse range of renewable stock from plants such as trees, grasses, flowers and sugars, and animal products like the gases from algae and bacteria from vegetable matter and waste.
Wood has been the basic fuel for fire for heating and cooking from time immemorial, with charcoal from wood being used for metal manufacture and processing.
Ethanol alcohol - has been used for many years as a fuel for internal combustion engines, produced from sugar and yeast, just as for wine and whisky, by countries, such as Brazil without native fossil fuel reserves.
Vegetable oils – from rape or sunflowers, either new or as recycled cooking oil – is being used as a substitute for diesel.
Methane - from manure and from landfill sites, is being used to both burn for heat or as a fuel for internal combustion engines.
Bio-fuel pellets, from waste wood and straw are now being processed extensively, and have fuelled the heating and power supplies of many wooden products’ manufacturers.
When all economically recoverable fossil fuels are eventually depleted, bio-fuels will be the only hydrocarbon energy resource, and alongside hydrogen from water the most ubiquitously available source for heat and power production.