Getting High on Grass – Can Plants Really Fuel a Plane?

Updated 11/09/2019

In the wake of recent studies showing how dangerously close to the brink we are when it comes to climate change, it is more important now than ever to seriously consider every possible alternative to environmentally damaging fossil fuels. One such alternative comes in the form of biofuels. Humans have been using biofuels for as long as we’ve been using wood to fuel our fires. In the last hundred or so years, however, we’ve begun to understand how plant matter can be converted into liquid fuels that could soon power a plane. In this piece, I’ll be looking at where biofuels are now and where they need to be if they are to significantly reduce CO2 emissions. I’ll be concentrating my efforts on recent attempts by the scientific community to make grass a viable fuel for transportation.

Grass is the most abundant plant on the planet. In my home country of Ireland, more than two thirds of all land is covered in naturally growing grass. If we could refine and perfect the process of turning grasses into fuel (grassoline), this could be a real contribution towards slowing the march of climate change. The problem right now is that it is expensive and inefficient. Many scientists in the field, however, think that given time and money, we could tap into this huge source of unharnessed power and perhaps help to save the planet in the process.

The reason grass in particular is being considered as a biofuel is not because it is necessarily the most efficient plant to use, but rather because of its abundance and willingness to grow in fields that are inhospitable to food crops, known as marginal lands. Another reason that grass is attractive as a biofuel is that it is not really needed for anything else. Other candidates for biofuels (like wood, sugarcane and soybeans) have the disadvantage of being useful for things like furniture, rum and tofu.

But why aviation fuel? One reason is that while cars are slowly turning electric, it is unlikely that planes will follow suit any time soon. This means that in the near future, cars could be powered by renewable sources whereas planes will continue to require liquid fuel. The other more pressing reason is that travelling by plane is far worse for the environment than any other mode of transport. This is down to two factors; first, planes are less efficient than other modes of transport in terms of emissions per passenger mile. Second, planes allow us to travel a far greater number of miles than we would otherwise be able to travel. The carbon footprint of flying from London to Hong Kong and back again is about a quarter of the average UK person’s annual carbon footprint.

The idea that we could use grass, algae and other plants to produce aviation fuel is not nearly as crazy as it sounds. The fossil fuels which we currently use are themselves made of organic matter that has, over a very long time, undergone a natural process called pyrolysis. Human beings have been using the process of pyrolysis for our own gain for thousands of years in the form of charcoal burning. Pyrolysis involves separating materials into their constituent molecules in the absence of oxygen. This means, very roughly, heating up the material to a specified temperature, covering it, and allowing it to separate into liquid, solid and gas. These products can then be refined into fuels. Recently, it has been found that microwave heating produces a higher pyrolysis yield than traditional methods since it can be done entirely in the absence of oxygen and at a very precise temperature. Another benefit is that the characteristic ‘hot spots’ of microwave heating aid in pyrolysis.

You might be thinking that grass is an important source of food for livestock. The beauty of using grass as a biofuel is that this resource would not be lost. The solid by-product of grass pyrolysis can still be fed to livestock. What’s more, by removing the liquid constituents, the feed can be preserved much longer than fresh grass cuttings. In the UK, biofuels already account for nearly 3% of all road and non-road mobile machinery fuel, but with the predicted change in efficiency given a few years, they could eventually account for a lot more than that.

Right now, scientists can only produce a few drops of biofuel from grass in the laboratory. Tests carried out at Ghent University in Belgium show, however, that there is a potentially very efficient energy source in grass if we can learn to harness it correctly. In April 2017, the researchers at Ghent found that a certain type of bacteria (clostridium) can be used to metabolize certain grasses into decane, a key ingredient in both petrol and aviation fuel. While this breakthrough cannot yet be used effectively, it is key knowledge that will inform future research into better biofuel technologies.

Hang on, you might say, if refining plant matter gives us the same fuel as we are already using, then why is it better for the environment? Surely biofuels release the same amount of CO2 as fossil fuels? This is indeed true. The difference is that the CO2 in living plants has only recently been absorbed from the air by the plant and is simply being released again. As the grass grows, it sequesters CO2 from the air. When it burns, that recently absorbed CO2 returns to the atmosphere to be trapped by the next batch of grassoline. Because of this, biofuels are said to be ‘carbon neutral’. With fossil fuels, the CO2 has been absent from the environment for a very long time, trapped underground. By burning it, we are releasing extra CO2 rather than what was already there.

A major obstacle to biofuel efficiency growth is that governments and companies are not willing to invest heavily in something that may not yield solid results for years to come. This is simply short-sightedness. The science will continue to improve. Lack of investment only slows down the process. The people who invest heavily now will surely see a huge return in a matter of years. Another well-known obstacle in the way of all renewable energies is the huge sums of money tied up in the fossil fuel industry. The industry is worth about 7 trillion USD globally. No wonder, then, that lobby groups are able so easily to sway policy-makers.

Biofuels are controversial among environmentalists, since they come with a number of downsides. Perhaps the most worrying is that every square foot of land which is used to produce the fuel is land that could instead be used to nurture biodiversity. Species are currently being lost so quickly as to constitute the sixth mass extinction in earth’s history. For me, using food crops like corn as feedstock is entirely off the table, since it opens the door to a future in which rich elites use corn-fed biofuel to fly away on their holidays while depriving poor people of food which is vital to their survival.

Another drawback is that biofuels are not very efficient when it comes to land use. According to Mike Berners-Lee, using solar panels instead to generate the power for flying would require 270 times less land than growing wheat for biofuel. The problem, however, is building a good enough battery. Right now, 1 kilo of jet fuel carries about the same energy as 20 kilos of premium lithion-ion batteries. One ray of hope came in March of 2015; ‘Solar Impulse 2’ began its attempt to become the first entirely solar powered plane to fly around the world. The journey was arduous and long for the two pilots. One of the pilots was named Bertrand Picard, a Swiss medical doctor who who was already the first person to fly around the world non-stop in a hot air balloon. Captain Picard of the USS Solar Impulse finally landed the plane in Abu Dhabi on July 26th 2016, from the spot where it had departed 505 days earlier.

Regardless of what figures like the US president may say, climate change is a very real and very serious danger. Biofuels are just one example of the many ways in which we can combat this danger, but they are one which will continue to grow in importance for years to come. The question is whether our money would be better spent developing renewable energies like solar and wind which require far less land and are thus better for wildlife conservation. When it comes to planes, however, grassoline may help to ease the transition to a low-carbon world. Every little helps in the fight against the huge and menacing entity that is climate change.

Some Further Reading and Research Sources

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