Explainer series: Biofuels 101

Biofuels can play a key role to wean us off fossil fuels, but the concept of using farmland to produce fuel instead of food has attracted controversy and scrutiny. A proposed mandate here in Aotearoa New Zealand aims to utilise this opportunity while sidestepping negative unintended consequences.

Types of biofuels and their uses

The term ‘biofuels’ refers to any fuel that is derived from plant or animal matter, in contrast to traditional fuels formed by geological processes commonly known as fossil fuels. Broadly, biofuels can exist in solid, liquid, or gaseous forms, just like fossil fuels. These biofuels are then categorised as first, second, third or fourth generation based on their feedstock (i.e. the raw material used to fuel the process). International food shortages, tensions around best land use and food security issues have seen the use of first and second generation biofuels vigorously debated.

Figure 2: an outline of the generational differences of biofuels. Source: Toitū (2022)

Many biofuels are blended with conventional fuels when used. How much biofuel is blended depends on the type of biofuel being used and the impact on the engine - oil companies and automobile manufacturers have provided input to regulate blending limits due to the potential for corrosion of equipment at higher blends (Karatzos et al., 2014). Using higher blends requires more frequent replacement of engine components, such as fuel lines. For aviation and marine fuels, performance at different temperatures is also a factor. Blending limits begin at about 5-7% for biodiesel, and around 10% for bioethanol. For marine biofuels, blending limits also sit at around 7%.

Drop-in biofuels refer to biofuels that may be used ‘neat’ without need for blending. These advanced biofuels should be distinguished on their direct use with existing infrastructure, removing the need for additional distribution channels required for bioethanol and biodiesel. Third generation drop-in biofuels are the strongest contender for a fossil fuel substitute – they may be produced from agricultural or forest resides, energy crops or municipal solid waste and algae. Routes to manufacturing these advanced biofuels are still to be commercially proven (Scion, 2018).

Figure 2: Life cycle diagram for biofuels. Source: Dunn et al. (2017)

The importance of life-cycle measurement

Life cycle measurement takes a cradle-to-grave approach to estimate impacts from a product or service. It’s important we understand the full picture of our decisions, not simply what is occurring when a product or service reaches our sphere of influence. Life Cycle Assessment (LCA) has been particularly useful to understand both the production and combustion impacts of biofuels (see Figure 3). This helps develop a full picture of the life cycle emissions and to understand where ‘burden shifting’ might occur (i.e. the creation of one environmental burden by attempts at solving another). Some biofuels have significant upstream production impacts due to land use impacts associated with growth of biofuel feedstocks. Production impacts include use of nitrogen fertilisers, which contribute to nitrous oxide (N₂O) emissions, a potent and long-lived greenhouse gas.

Figure 3: Emissions associated with different types of biofuels. Source: Comendant and Stevenson, 2021

LCAs can also provide an understanding of the impact of blending on biofuel’s potential for carbon reductions. Essentially, the blending of biofuels at low rates of 5-10%, yields minimal benefit in terms of greenhouse gas emissions. Additional impacts may occur outside climate change. Impacts to biodiversity, water resources, and competition for food must all be considered. LCA studies therefore conclude that advanced biofuels from forestry residues and energy crops (within the ‘second generation’ category) are the most beneficial, as they have low land-use impacts and can be incorporated at higher blends (Comendant and Stevenson, 2021). By contrast, those produced from vegetable oils are associated with the highest emissions. Biofuels sourced from vegetable oils have, in some studies, turned out to have higher emissions than fossil fuels across the life cycle (Comendant and Stevenson, 2021)!

NZ’s roadmap for biofuels

Advantages of using biofuels in New Zealand have long been discussed, and since have matured into a mandate proposal. A Scion ‘Roadmap for Biofuels’ in 2018 provided some key insights, suggesting use of biofuels only where there were few decarbonisation options, with a preference towards drop in fuels for heavy transport, marine oil and aviation. The electric revolution for passenger cars was expected to remove the need for biofuels to replace fossil fuels for personal transport by New Zealanders.

Glossary