Biofuels are one of the many approaches being tried to solve peak oil, all the word means is fuels derived from organic matter (organic in this case means from living things, generally plants). To explain why we’re trying I have just pulled out a paragraph from my chemistry textbook from the chapter on biofuels (it’s a small chapter and they’ve just added it recently). I find it surprisingly honest about what’s happening for its source
‘Peak oil’ is the time when worldwide oil extraction can no longer keep up
with increasing demand.
The greatest amount of oil discovered in any one year was in 1964,
and since then the new reserves found have gone down in size each year.
Meanwhile demand for oil has increased as the world population has
increased and lifestyle expectations have risen. The actual timing of ‘peak
oil’ is debatable. We may be there now!
The situation provides motivation to devise renewable and sustainable
sources of the carbon compounds, both for fuels and to provide feedstock
for the organic chemical industry.
The statement above is mostly accurate but many of the realities of biofuels are ignored and need to be stated here. It uses agriculture that generates chemical energy as a fuel rather than as food, it suffers from the limits and faults of any agricultural system used to produce them and will change along with the rest of the agricultural system. It also competes with food production, which limits the production levels. While alternatives to using food are available, most of them suffer drawbacks and would still require nutrient cycling to remain sustainable.
Now the dominant form of agriculture is the industrial from, which suffers from an acute case of unsustainability. So, any biofuels produced under the current model also suffers from a case of unsustainability. Of more concern is the fact that the current agriculture system uses vast quantities of fuel energy and so any biofuel production would first have to compensate for its own production. Since the fuel use of industrial agriculture is so high this means that most biofuels produced today have a low or nil EROEI. High EROEI biofuels are produced mostly by hand labour (e.g. ethanol from Brazil) and can reach about 10. This means that replacing current farming practices with the various organics modes before introducing major biofuel production is the better option, since the supporting system is figured out first and it can then be decided if it is worthwhile.
Biofuels also can’t replace petroleum and other fossil fuels in both amounts and usage. This doesn’t make them worthless, just that their role will be highly limited and needs to be supported with other energy sources.
So what are the biofuels?
Solids: The oldest biofuels, traditionally wood, normally used for fire & cooking, there are currently efforts to increase the range of sources of solid biomass available for heat energy. Charcoal is a refined form of wood and was used extensively in metalworking and glassworks. It’s actually superior to coke but costs more and its increased use caused large scale deforestation across large areas in Europe and America. Any organic material can be used as a feedstock for the new types being invented and as long as proper nutrient cycling takes place long-term soil fertility won’t suffer. Raw biomass does create large amounts of pollution however, which limits desirability.
While it will not easily power motor vehicles (except electric or trains), it can easily supply heat in stationary operations or electrical/mechanical power production. Due to its difficulty to transport (relative to liquid fuels), the main constraint on use will be its availability in the immediate area and rural areas should have the greatest access while cities will probably use it as a small supplementary energy source at best. For military use, mostly cooking, supplementary heat and a local source of electricity.
Biogas: The chemical of interest in biogas is methane, which is identical to natural gas. This allows the use of existing infrastructure of natural gas to be directly used with only 1-2 components added. The production of biogas, anaerobic digestion of biomass, has two products; a solid known as digestate, which can be used either as a fertilizer or as fuel (fertilizer will be the default option) and a mixture or methane, hydrogen, hydrogen sulphide (corrosive) and carbon monoxide gases. This is one of the easier biofuel production processes and is relatively simple and cheap (the Chinese are engaged in massive biogas programs).
When upgraded (takes 3-6% of the energy in the gas to upgrade) it can power machinery without corroding it, hydrogen sulphide isn’t a very nice chemical. Compression into a liquid can allow easy use in vehicles and has been shown to be able to power trains (Sweden), this also makes it a candidate for military use. Like all biofuels, rural areas will have the greatest access but thanks to its ability to be transported easily by pipes a connection to the rural hinterland could allow a reasonable supply to cities; this also counts for the liquid biofuels.
Fuel cells offer a highly efficient way of converting methane directly into electricity as opposed to using hydrogen.
Ethanol: otherwise known as alcohol and is made by yeast fermenting sugars anaerobically. Comes in a liquid form, which makes it directly usable in combustion engines; either as an additive or (in Brazil) as the fuel, some engines do need modifications through (it can melt plastics). By-products of production can be used a animal feed (high in protein) or fertilizer but carbon dioxide is also produced. Improvements, like GM bacteria that can use waste products or special breakdown process of plant cellulose, are happening and could help keep basic (limited) motorized transport running. Would most likely be produced in abundance by Queensland’s sugar cane crop, similar to Brazil’s approach.
Isn’t as good on the engine as gasoline is, but it can be used for fire quite well. E.g. http://www.ozflame.com.au/. Most likely, it won’t be used as the primary combustion fuel (biodiesels are better for that) but it can be used as a solvent, as an antiseptic, chemical feedstock and as a drink.
Biodiesel: Is produced by the breakdown of triglycerides by Tran esterification (breaks a lipid into 3 fatty acids and a glycerol). Energy density is close (about 9% lower) to petrodiesel but it does offer a higher cetane rating (combustion quality) and better lubricating qualities which helps offset its disadvantages.
Due to the higher energy densities and increased efficiencies of diesel, biodiesels use in heavy machinery, armoured fighting vehicles and ships is likely, if biofuels are used for the military it will most likely be the primary fuel used. Can also power aircraft and in rural areas would provide heavy muscle to add to the other energy sources available. As a sidenote, from the crushing of oil seeds a high protein and carbohydrate meal residue is produced which can be feed to livestock, this makes it more attractive for farms to produce the Biodiesel for themselves.
Usage Levels and Nutrient Cycling: Two important questions remain about biofuels, how do they fit in the energy mix we’ll have during the transition and ecotechnic phases and how the nutrients used will be cycled back into the soil.
To understand how nutrient cycling will work I’ll list the elements of the fuels and where they come from. For ethanol the nutrient used is glucose which is made of Carbon, Hydrogen and Oxygen, all the fuels contain only this elements (if the fuel is pure) and Charcoal is only Carbon while biogas is Carbon and Hydrogen. In sugar production water is split in the chloroplasts by light (artificial photosynthesis is an attempt to copy this process) to form Hydrogen and Oxygen. The Carbon comes from the Carbon dioxide in the atmosphere around the plant and is used to form the backbone to which Hydrogen and Oxygen is attached. Therefore, as long as only the fuel is leaving the farm or local area the plants via the atmosphere can replace the nutrients. Of course, the soil normally gains these nutrients when the plants die and taking them away will make the soil poorer than it would otherwise be. The principal loses are organic carbon and a source of energy (that is what sugar is after all) for the soil organisms and in some way this needs to be compensated, leaving the land fallow could work and there are undoubtedly other approaches suited to each area, biochar could certainly compensate for the lowering of organic carbon levels.
The usage of biofuels will depend on the traits of other energy sources as much as its own traits. Given that wind and solar suffer from intermittency while biofuels can be used whenever you want (after production) then a compensatory role is likely. This also fits with their ease of storage relative to wind and solar, similar to granaries but for energy instead of food. Balancing the amount of food storage with energy storage (since it can be converted only one-way) will be tricky and a vital decision of any society that seeks to employ biofuels.
For storage, a good system could involve two levels. The first level could be considered the day to day use (or in this case year-to-year) and is for individual farmers and towns to supplement other energy sources. This would carry over from month to month and partially from year to year and provides the main usage for everyday life. The second level is made from the surplus from the first storage level and is used for the bigger regional/national energy expenditures. While the first level is used for yearly famines the second can be used for multi-year famines, in effect they allow no biofuels to be produced that year without losing energy, that the first level couldn’t cover. This second level would cover major infrastructure expansions/maintenance and such, major wars, festivals and other big energy expenditures.