Sustainable fuels or not?

Today, a Swedish study affirmed that biogas is the most environmentally friendly fuel. Last week, another study stated that it is more environmentally friendly to run the vehicles on fissile fuels than bio fuels. Last month, a third study of “Green Protectionism in the European Union” claimed that the subsidies for sustainable fuels is a threat to the free trade and that it disrupts the market to less environmentally friendly fuels “such as ethanol or biodiesel”. How come that different studies come to such different conclusions?
When reading different studies the scope varies a lot.
If you put the question which fuel is the most environmentally friendly for buses? You can put a boundary just looking at the usage on the bus and find that the efficiency of the engine and the emissions varies for different fuels. Sometimes different vehicles are compared but very rarely the use of the fuel in sectors outside the vehicle sector is considered.
In a similar way the fuel production can be put in relation to other useful products with another environmental impact. Depending on how broad the scope is very different conclusions are achieved.

The figure depicts different boundaries and scopes leading to different conclusions when the environmental impact is analysed. In general the darker the box the less frequently the aspect is considered in the literature. Very rarely the most efficient use of the money is analysed.
It should be noted that the answer is not converging to one “optimal” answer the broader the scope is. For example biogas made from waste may even have a positive impact since the waste would generate methane that is considered to have higher impact than the carbon dioxide resulting from the combustion of the biogas. But, with a limited availability biogas comes out as favourable for all vehicles and all power generation. Could it be that it is more efficient to use the biogas in a combined heat and power plant?
To refer to the provocation in the title, it is not obvious what is most sustainable when it comes to fuels. A hypothesis say that farmer will grow what ever gives them the highest income. In the same way raw material for bio fuels and other bio based products compete on the same market. Simultaneously the energy market is essentially global and the market price for oil and coal, being the most mobile energy, sets the boundaries for the energy price.
Therefore the use of bio fuels needs to consider all potential use of land, energy and biomass to derive to a reasonably consistent conclusion considering the potential sustainability. 

About volvobuses

Adjunct Professor of Catalysis at Chalmers University of Technology. Lives in Gothenburg, Sweden, with my wife and three daughters born in 1991, 1994 and 1997. Is a passionate runner.
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