When we say biofuels, what do we actually mean?

Did you know that the simple three-letter word “set” has the most definitions of any verb in the English language? The Oxford English Dictionary lists 262 definitions of its use as a verb and 64 as a noun although it grudgingly concedes that maybe some of these definitions are a tad obscure. Still, it is an astonishing number of meanings, followed closely by another three-letter word, “run”, which is coming up hard on the rails with 245 uses as a verb and 109 as a noun. In our small micro-world of renewable energy, a similar tiny word “bio” is increasingly gaining a plethora of meanings and seems to prefix pretty much any one of eight different renewable fuels. This gives rise to a lot of confusion; for example, between biomass and biogas or bioethanol versus biomethanol. They are all different things so in this brief blog, we shall try to make sense of what the eight different biofuels actually are, how they are made, what they are used for and why, in their different ways, they may not be quite such the good thing they are commonly perceived to be.

The simplest and oldest form of biofuel is biomass. Obviously, this is burning bits of wood either to make steam and then electricity, or just to be used as a cooking and heating fuel. People have been burning wood for cooking and heat for about 1.5 million years now, though in the developed world, this seems to have become the preserve of middle-class liberals like me with our Aga and wood-burning stove. This fad is increasingly seen as a source of air pollution and I expect domestic wood-burning stoves will be outlawed within the next five years. The use of biomass to make electricity is equally controversial. A common misconception is that the whole swathes of US forest are being cut down, turned into wood pellets and shipped across the Atlantic to be used as biomass. The reality is more prosaic and the bits that get pelletised are the smaller branches and twigs which are far less valuable than the main trunk of the tree, which gets turned into useful products such as joists and furniture. Nobody is grinding up big tree trunks into pellets, but this myth still prevails in the right-wing press. About 15% of all wood produced in the US is used for energy which, as you can easily tell by looking out of the window, is a lot less than the branch/trunk weight ratio of a typical tree.

The second most common biofuel is bioethanol. This is made from distilling crops such as sugar beet into alcohol. Like burning wood, this is another human activity that has gone on for a long time, although more for recreational purposes than for cooking or heating. Globally, we produce about 30 billion gallons of bioethanol per annum and it is blended with fossil fuel-based petrol. Imposing blending obligations on fuel producers have become very popular with governments as a quick and cheaper route to decarbonising the transport sector. In the UK for example, the E10 regulation requires, as the name suggests, a 10% ethanol blend for all petrol sales. Blending obligations seems like a good idea but critics say they distort agricultural markets and create mono-crop deserts which destroy biodiversity. We see this in the US where over 33 million acres of land is now used to grow just one type of corn to produce ethanol for petrol blending. To put that number into context, this is an area of land bigger than Belgium.

In a similar vein, biodiesel is another blending fuel. Biodiesel is primarily made either from dedicated crops such as palm or soy, or from used cooking oil and other fatty liquids. Global reduction in 2024 was 52 million tons and this is growing by about 6% per annum. Although it seems like a good idea, biodiesel is another controversial area. Most of the “used cooking oil” (UCO) in the world originates from China and the little word ‘used’ is doing a lot of heavy lifting in that three-word description. The worry is that the oil is being produced from soy or palm just to be sold into Western biodiesel markets and is not a waste product at all. Cutting down ancient native trees to clear the land for biodiesel production kind of defeats the renewable point of the policy and the issue of fraudulent UCO has massively undermined investor and government confidence in the biodiesel sector.

On a more positive note, making biogas from manure or food waste is gaining popularity with investors but fundamentally needs millions of tons of feedstock from industrial animal farming units. Furthermore, the word ‘biogas’ is commonly misunderstood. In essence, biogas is a blend of CH4 (methane) and CO2 and is burnt in engines to make electricity. Biomethane is made from biogas by separating the CH4 from the CO2 and the gas can either be injected into the grid or compressed to make bio liquid natural gas (bioLNG) for use in transportation. So biogas makes electricity which is different to biomethane which is a gas for cooking and heating which can also be made into bioLNG which powers trucks. Hopefully, that is a bit clearer.

Confusingly, biomethanol is a completely different fuel to biomethane even though they sound very similar and are only separated by two letters. To compound the confusion, biomethanol can be made from biomethane using steam methane reformation (SMR) so it is no wonder the terms get confused. Biomethanol is a relative newcomer to the biofuels party and global production is only 200,000 tons per annum. Biomethanol is another blending fuel although it is widely used is China as a cooking fuel. There is growing interest in using bio methanol as a form of Sustainable Aviation Fuel (SAF) and this is discussed further below.

SAF is the current hot topic in the biofuels world. The low energy density of batteries means electrification of pan-Atlantic jets is an awful long way off, so some form of liquid fuel will remain needed for years, probably decades. As with transport fuel, blending obligations are the main legislative driver and on a sliding scale over time, European airlines are required to blend up to 70% of their fuel with SAF by 2050. Even a 1% blend requires 5 billion litres of fuel per annum so this is going to be a huge market in the coming decades. There are a bewildering four common ways of making SAF: 1) by converting syngas made from biomass and waste products using the Fischer-Tropsch process, 2) by converting a fatty liquid like UCO, 3) by producing bioethanol, or 4) combining biomethanol with carbon monoxide produced from renewable electricity.

Although there is a lot of interest from the airlines in SAF, there is no consensus yet on the best way to make it. Gasification of biomass or municipal waste is a great idea, but people have tried and failed to make industrial-scale gasification work for decades and lost a lot of money along the way. Making SAF from UCO is controversial because of the issues of sustainability that have plagued the biodiesel markets and fundamentally, the two fuels are competing for the same finite feedstock. Similarly, bioethanol for SAF is a direct competitor with bioethanol used for blending petrol, and so requires even more land dedicated to growing corn. Biomethanol from biomethane seems to have potential, but there is a substitution question: taking an existing biofuel that is already used as a fossil fuel replacement and using it to power flights instead . So, what difference does it make? In terms of emissions per ton per mile travelled, planes emit far less CO2 than trucks so assuming a finite availability of feedstock, it is probably better to power the latter with biofuels rather than the former.

In conclusion, there is no single thing called biofuel. It is a collective noun for eight different fuels, all of which are made in different ways and often from different feedstocks. They all have a part to play in the transition to net zero energy systems, but they are far from the panacea that they first appear. Biomass is almost as old as human history, but it is not a transport fuel and there is growing awareness of the impact on air pollution of domestic wood burning. Growing crops and turning them into liquid fuels for blending seems like a good idea, but the seemingly never-ending mono-crop corn deserts of the mid-Western states of the US have had a devasting impact on local biodiversity and dedicating yet more millions of acres for SAF will only make this situation worse. Turning waste products into fuel also sounds sensible, but we have seen the law of unintended consequences play out in the UCO market, and anything that relies on gasification is probably still decades away from being investable. Biogas and its derivatives of biomethane and bioLNG seem less controversial but manure-based plants need a lot of feedstock, and this is only practical to collect if millions of animals are kept in big sheds.

Each of the fuels under the umbrella of the collective noun of biofuels has its challenges and we have yet reach a global consensus on the way forward so a lot of money will be invested and ultimately wasted in technical cul de sacs. This uncertainty probably needs to be played out before investors get wholly comfortable with the sector. We may only have eight types of bio fuel compared to 262 definitions of the word set as a verb, but eight is probably still too many to be practical as a way of decarbonising transport.