The need for sustainable energy has never been greater. From the 2015 Paris Climate Agreement to the UK government’s declaration of a Climate Emergency, it has become evident that the world is moving to take action to combat climate change and reduce greenhouse gas emissions. Of global greenhouse gas emissions, transport and shipping are responsible for almost 25%, due to the sector’s heavy dependence on fossil fuels (Nunez, 2019). Successful strides have been made to find and utilise renewable forms of energy such as solar and wind, but until it can be ensured that only renewable energy will power electric vehicles, there is still a gap in the market for reducing the emissions of the transport sector.
In the 2000s, large volumes of headlines pointed to bioenergy filling this gap in the energy of the future. Predicted to provide 10% of the world’s energy and a popular topic on GCSE geography papers nationwide, bioenergy provided a more sustainable alternative to the petrol and diesel fuels which power many vehicles today – without the need to replace the vehicle for an electric model, or to modify its engine (Dhillon, 2012). However, biofuels have had significantly less media attention in recent years; is this purely a coincidence or is there a reason behind it?
What is bioenergy?
The simplest definition of bioenergy is that it is the energy produced from using biofuels. Derived from biomass such as plant materials or animal waste, biofuels provide an alternative to their grubbier fossil fuel counterparts. Biofuels are classed into ‘generations’ to reflect the origins of their production. First and second-generation biofuels are those that are developed from edible (food or animal feed crops grown on arable land) and nonedible sources of biomass respectively. Algae-based biofuels fall into their own category: third-generation biofuels.
But what makes up a biofuel and how is it produced? Whilst there exists an extensive range of different kinds of biofuel, from Wensleydale waste to leftover corn husks, there are two types that appear to possess a greater potential for transforming the transportation sector (Ambrose, 2019). These are bioethanol and biodiesel.
Ethanol is not a new fuel; in fact, it has been around longer than the car (Associated Press, 2006). However, new discoveries of oil and gas sources have translated into very little attention being paid to ethanol for the most part of the 20th Century.
90% of global ethanol production begins with the fermentation of biomass (Yuan, 2018). Plants produce their own energy and food via photosynthesis; their intake of carbon dioxide and sunlight is used to produce glucose and oxygen. Any spare glucose is then stored as simple sugars or starches. During fermentation, yeast is added to the compressed and grinded biomass which results in the stored sugars being converted into ethanol and carbon dioxide.
The ethanol is distilled and dehydrated as extra would otherwise impact the purity of the ethanol and its ability to be blended with a range of concentrations of gasoline (Ethanol, n.d.). The bioethanol acts to reduce pollution in gasoline and increases the fuel’s octane rating, boosting its overall performance (Pacini, Pereira-Sanches & Durleva, 2014) .
Post-production issues can arise with the accidental contamination of the ethanol with water. Ethanol absorbs water from the atmosphere, making it a hygroscopic substance. Hence, extra care must be undertaken as, if water is taken in, it may cause phase separation within the mixture, increasing the risk of engine stall and damage to the engine (Russell, 2018).
Biodiesels are a vegetable oil- or animal fat-based alternative to traditional petrol and diesel. The term excludes the direct use of unmodified or waste vegetable oils (or in some very strange cases human fat!) which require converted engines (Adams, 2008). Examples of biodiesel sources include first-generation rapeseed and palm oil as well as second-generation jatropha oil (Divakara, Upadhyaya & Wani, 2010).
Biodiesel can be used in its pure form or added to blends with traditional diesel.
Can biofuels meet global needs and demands?
To answer this question, one must first consider the needs and demands that need to be met. Current petrol and diesel fuels release large quantities of greenhouse gases and release pollutants and particulates when burnt. Any new fuel must improve on these factors whilst also remaining cost-effective and not compromising the security of other vital industries, such as food.
The surface level argument for the emission reduction ability of biofuels is that they are carbon neutral. The biomass feedstock sequesters carbon as it grows and releases equal quantities when burnt. But this view is too simplistic as it fails to take account of the lifecycle emissions, the energy required to grow, harvest, transport and convert crops into biofuels. To be a truly valuable form of renewable energy, bioenergy must have significantly lower lifecycle emissions than its fossil fuel counterparts (Abraham, 2018). Current studies analysing lifecycle emissions suggest that biodiesel reduces carbon emissions by 20-80% when compared to traditional petrol and diesel. Whilst the uncertainty in this prediction is unsettling, this reduction is expected to grow as crude oil reserves begin to deplete, oil extraction processes become even more energy intensive, and second-generation biodiesels begin to take a larger market share (Tabatabae, 2019).
Biofuels may also impact air pollution levels. The principal difference between biodiesel and petroleum diesel is the added presence of oxygen in biodiesel from the additional ester. This improves the octane rating of diesel and hence the fuel performance, but simultaneously reduces the energy content per volume (Behera & Varma, 2019). The additional ester also allows for a more efficient burn and, as there is more oxygen to create carbon dioxide, less carbon monoxide is released. The burn is also associated with lower levels of sulphur oxides and other volatile organic compounds, all key air pollutants (Pacini, Pereira-Sanches & Durleva, 2014). When added to petrol blends or used on its own, bioethanol is associated with a reduction in the same pollutants as biodiesel, but with a significant increase in the levels of the unregulated pollutant acetaldehyde (D.E.F.R.A., 2011). Biodiesel is also linked to a small increase in nitrous oxide emissions, an increase correlated with the strength of the biodiesel. Overall, whilst biofuels at low strengths, such as 15%, are considered to cause little change to air quality, there is a great deal of uncertainty still surrounding higher strength biofuels (D.E.F.R.A., 2011).
Albeit with some uncertainty in the magnitude of their impact, biofuels tend to have a greenhouse gas emission reduction effect, with little change in contribution to air pollution to traditional petrol and diesel. They also hold a distinct advantage in that they can be used in current petrol and diesel vehicles without engine modification, potentially allowing for a smooth transition. However, the secondary effects of biofuels on the world must be taken into consideration.
A common argument against biofuels is that they pit food against fuel in competition for land. A prime example of this effect is in the USA where, in 2007, 25% of the corn harvest was set aside for bioethanol production (Kingsbury, 2007). As arable land is diverted for fuel production, this can cause food shortages and drive up food prices (Mitchell, 2008). Notably this effect is most likely to be felt by the poorer communities, bringing into question the sustainability of such fuels (Behera & Varma, 2019). This is where second-generation biofuels make their appearance. Chosen as to not compromise food security and to require little fertiliser and energy to produce, second-generation biofuels are a more sustainable advancement on their first-generation counterparts.
There is also an argument that biofuels could result in an increase in deforestation if farms expand to be able to cater to both food and fuel demands. 17% of anthropogenic greenhouse gas emissions each year are linked to changes in land use, which could undermine the emission reduction ability of biofuels if preventative policy is not put in place (Wade-Ross, Grunwald & Brenton, 2016). Encouraging the growth of biofuel feedstock on marginal land, which does not possess much potential for farming of edible crops, and moving towards second-generation biofuels, which allow for the combination of food and fuel production, could counter these concerns, a move the EU has already begun to make (European Parliament, 2017). For example, corn husks can be used for second-generation bioethanol production without impacting the extraction of corn for food or using additional land.
Ultimately, however, these causes of concern may not materialise fully if biofuels do not possess the ability to meet a significant portion of the world’s energy demand and remain cost effective. And do they? The short answer to this question is maybe. Predictions of the potential energy availability of biofuels range from 1550 EJ a year, three times the worlds current demand, to just 61-161 EJ a year (Offerman, Seidenberger & Thrän, 2011; Searle & Malins, 2014). Not only are these estimates reliant on using first-generation fuels, but this uncertainty is unlikely to change without further research and development. As for maintaining their cost effectiveness, so far only first-generation biofuels using farmland have been able to achieve this, with second-generation biofuels currently unable to keep up with traditional fuels in terms of scale and cost (Nunez, 2019). However, they remain a cheaper, more sustainable option currently for those unable to purchase a new electric vehicle.
What role can bioenergy play in the future?
Although bioenergy is well understood, its real-world implications and uncertainty in its energy potential, limit the confidence that can be placed in it. It’s capacity to become a leading component of the energy of the future is reliant on the use of sustainable second-generation feedstocks and the transparency of the supply chain to ensure this. Further research is also required to assess the lifecycle emissions of emerging biofuels as improvements are made.
But the factor of time cannot be avoided. The clock is ticking for governments to make serious changes to avert climate catastrophe and, whilst other forms of sustainable transport, such as electric and hydrogen powered cars, are advancing, the current pace suggests that there is still a significant period of time ahead where petrol and diesel cars will continue to dominate the roads. It is here that politicians, scientists and policymakers will need to consider the advantages and disadvantages of encouraging the transition to a more, but not completely, sustainable fuel where there is significant uncertainty in its impacts. Is a quick fix a true solution, or is it this very attitude and the abandonment of the precautionary principle that led to the escalation of the climate process in the first place?
Header image: Photo by Philipp Katzenberger on Unsplash
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