Biofuel for tractors

Today, most agricultural tractors and other machinery operate on fossil diesel fuel. This has however not always been the case. Before the 20th century, the use of fossil fuels was rare in agriculture. Animals such as horses and oxen were commonly used as a power source, and still are in many developing countries. To fuel these power sources, renewable energy is needed in the form of animal feed. As a rough estimate, about 20% of the arable land was in Sweden used as feed for the draught animals in the 1920-ties, not so efficient in other words.

Steam-powered tractors were developed in the early 20th century, but were soon replaced by petrol- and kerosene-powered tractors. In a period during World War II, the use of liquid fossil fuels for tractors was restricted due to supply limitations. In Sweden, the problem was solved by converting tractors to operate on wood or coal gas. (I found a person still busy with it! In the 1980s, the use of vegetable oils as tractor fuel was given a lot of attention. Research was (and is still) also being conducted on ethanol and biogas for use in tractors. This is a link to the history of the tractor

In a European Union funded project, a solar-powered agricultural vehicle has been developed. Batteries are charged up with solar power and used in small agricultural vehicles up to 40 hp. Very interesting! Perhaps a bit difficult in a Swedish context but seems to work well in Italy where it is tested.

A very interesting new project is the concept tractor released in 2009 by the manufacturer New Holland; a fuel cell 75 kW tractor operated on compressed hydrogen stored in an integrated tank under the hood. The use of fuel cells in tractors is not a new concept however, as the world’s first fuel cell vehicle was a tractor built in 1959 by Allis Chalmer. It was equipped with 1008 individual alkaline fuel cells and had an output of 15 kW of electricity.


Left: the first fuel cell vehicle in the world, an Allis Chalmer tractor built in 1959 (photo courtesy of Science Service Historical Image Collection). Right: the new fuel cell concept tractor built by New Holland in 2008 (photo courtesy of New Holland).

First, second and third generation renewable tractor fuel
Most agricultural tractors, harvesters and other machines operate on diesel. The production of alternative fuel for tractors would therefore be the same as for any other diesel vehicle. There is however differences on the supply side since most farms use much fuel in the intensive harvest and plant seasons. This makes it tricky for farms to be self-sufficient in fuel as large amount of fuel has to be stored.
Although there is no official classification of renewable fuels into groups, it is common to refer to first, second and third generation fuels. First generation renewable fuels are usually defined as those that can be produced with current technology on a commercial scale. Ethanol is produced via a fermentation process from sugar-rich crops such as sugar beet and sugar cane and from starch-rich crops such as cereals. Fatty acid methyl esters (FAME), sometimes referred to as bio-diesel, also belong to the first generation fuels. An example of FAME is RME, produced from transesterification of rapeseed oil. FAME can also be produced from animal fat, palm oil, soy oil, etc. Biogas from anaerobic digestion of crops and waste is also referred to as a first generation fuel.

Second generation renewable fuels are usually defined as those fuels that are not yet produced on a commercial scale. Examples are ethanol from lignocellulosic material and fuels produced via thermochemical gasification of non-food biomass and waste such as Fischer Tropsch diesel (FTD), dimethyl ether (DME), hydrogen and methanol.

Sometimes even a third generation of renewable fuels is mentioned, defined as new and hybrid processing technologies that convert organic materials to fuels. This includes for example cultivation of cyanobacteria or microalgae that produce hydrogen. Artificial photosynthesis is also a promising concept; research is being conducted to imitate the enzymatic process that green plants use to capture sunlight and split water molecules into oxygen and hydrogen.