Biofuels
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Description
A biofuel is some form of renewable fuel derived from vegetable or animal sources, as opposed to fossil fuels.
Detailed description
There are many forms of biofuels, ranging from cow dung or wood used in an open fire through to gas or liquid fuels manufactured from vegetable or animal matter. This article will deal principally with liquid fuels but will also touch lightly on some other biofuels.
The energy balance of purpose-grown biofuels is something that must be carefully studied. It would be ridiculous to make a biofuel if doing so requires more energy than the energy it contains. An energy balance sheet therefore needs to be established (as well as the costing). On the assets side, we have the energy that can be obtained from the finished fuel when it is combusted. It would be useful to convert this into the equivalent volume of a conventional fossil fuel, to ensure like is compared with like. On the liabilities side, we have a number of positions, involving the energy required to:
- manufacture chemical fertilisers and transport them to the growing site
- transport the seed
- plough and prepare the land
- pump irrigation water
- manufacture, transport and apply pesticides
- harvest the crop
- transport the crop to a processing plant
- process the crop into a usable fuel
- process and dispose of the residues and other waste materials
- transport the fuel to a blending plant.
Another point which is even more controversial is the fact that most biofuels are grown on land previously used for growing food crops, therefore artificially causing a penury of food and increasing the food prices. The MIT has published a report [1] claiming that price of tortillas in Mexico has doubled as a result of US corn being diverted to ethanol production. Another serious report [2] echoes this sentiment and adds "...the biofuel industry has long been dominated not by market forces but by politics and the interests of a few large companies." Biofuel, and especially ethanol, production is not economically competitive, compared to fossil fuels, and many countries directly or indirectly subsidise it, either by cash payouts or taxing imports. One possible exception, from the point of view of energy, is ethanol from sugar cane, which may just have an EROEI slightly greater than unity but the Brazilian production has destroyed large areas of Amazonian rain forest and unique wetlands.
Biodiesel made from vegetable oil is also usually manufactured with an EROEI of about unity, whether from rapeseed (colza, canola), hempseed, sunflowers or oil palms.
The one exception where biofuels may be positive is in the case of large composting projects of animal or vegetable waste, where the gas is collected and the methane separated and used as natural gas. The composted material may be used as a bio fertiliser, reducing the need for chemical fertilisers, which require fossil fuels for their manufacture.
