To achieve net zero greenhouse gas (GHG) emissions in agriculture a shift from the predominantly diesel-powered farm vehicles of today to low carbon alternatives will be imperative.
Diesel has been farming’s primary fuel for generations, since the industry was one of the first to adopt the novel form of propulsion that Josef Diesel introduced around the turn of the 20th century. Now, the future of diesel and other fossil-derived fuels is limited, as the agricultural industry gears up to achieve net zero GHG emissions.
There are several candidates for farming’s ‘fuel of the future’. These include electricity generated using renewable resources, biomethane and hydrogen.
Electric vehicles for agriculture
Battery Electric Vehicles (BEVs) run purely on electric power, stored in an on-board battery charged from mains electricity or a battery recharge system located where it is used, including on farms. BEVs release zero tailpipe emissions, which means they do not emit GHGs or air quality pollutant emissions such as particulates or NOx from the exhaust. When powered by renewably generated electricity, BEVs are classed as a net zero technology.
While renewable electricity can be generated on farms via solar panels, wind turbines or biogas combustion, the energy density of batteries remains a barrier to electricity replacing diesel as the fuel of choice for farm vehicles. The added weight of batteries needed to provide the necessary power-to-weight ratio for larger agricultural tractors (i.e. >50 hp) limits engine efficiency and damages the soil.
On-board batteries used to power tractors must be able to deliver sufficient power to undertake farm tasks. They also need sufficient capacity to operate for a full working day. At busy times like silage making, harvest or drilling, that could mean 16-hour working days - which leaves just eight hours for re-charging the batteries. While this can work for smaller BEV’s such as vans, compact tractors or other automatic machines, but for heavy vehicles, recharging times are simply too slow.
Despite the challenges, BEVs could have an important role to play on farms in the future. Smaller robotic machinery platforms can operate very efficiently with renewable electricity generated on-farm from solar panels, wind turbines or biogas combustion. The emergence of digitally controlled driverless technology and the need for more environmental and resource-sensitive field operations will lead to a revolution in vehicle design. With a move to low- or no-till agriculture, lighter, smaller automated vehicles which are more suitable for electrification could become more widespread on farms and in horticultural enterprises. Find out more on how autonomous vehicles can be used in farming here.
Biomethane is the renewable equivalent of natural gas (CNG). It can be produced on-farm by breaking down organic residues using anaerobic digestion, then removing the CO2 from the resultant biogas in a process called biogas upgrading.
Compressed biomethane (bioCNG) is a relatively mature technology. Road going vehicles have been run on methane for several years in the UK. BioCNG does not need to be grid injected and can be dispensed at farm production sites and can also be distributed to other farms using biomethane trucks. BioCNG could initiate more rapid transport decarbonisation and its use on farm could help reduce methane emissions for livestock farms, if supplied from on-farm biogas plants. Rural biogas plants could install upgrading and biomethane re-fuelling stations immediately and offers a ready-for-use diesel replacement, in advance of development of viable BEV or hydrogen (H2) power trains. This makes biomethane one of the best options for rapid decarbonisation of farm transport.
In addition to biomethane there are other biofuels which can potentially be used in farm vehicles. These are:
- Renewable biodiesel - also called fatty acid methyl ester (FAME), renewable biodiesel is produced from waste vegetable oil with methanol. Vehicle manufacturers approve the use of blends up to grade B30 (30%). Several tractor manufacturers offer engine configurations for grade B20 (e.g. John Deere) and some can use higher blends (e.g. Deutz).
- Hydrogenated Vegetable Oil (HVO) - chemically similar to conventional fossil diesel, HVO is a ‘drop-in’ fuel that can substitute for diesel with no operational impact. Due to production cost, HVO is likely to remain a niche alternative fuel.
- Synthetic fuels – these are at an early development stage. It is possible for industrial processes to combine electrolysed hydrogen with CO2 to produce a synthetic fuel. However, completing this process at scale with a reasonable cost to end-users such as farmers is challenging. At present, synthetic fuels struggle to compete on price against other power solutions.
Hydrogen can be used either in an internal combustion engine (ICE) or in a fuel cell to drive electric powertrains. Green hydrogen can be produced by using surplus renewable energy, such as solar or wind power, to power the electrolysis process which splits water (H2O) into hydrogen and oxygen atoms.
Hydrogen is proposed as a long-term diesel fuel replacement for heavy vehicles, including in ICEs. Based on real-world observations of road-going fuel cell vehicles by Cenex, fossil fuel derived hydrogen can achieve up to 50% reduction in GHG emissions compared to an equivalent diesel vehicle when used in a fuel cell. Similar GHG emissions reduction should be possible in agricultural equipment powered by fuel cells, should these become commercially viable. If powered by renewably generated green hydrogen, fuel cells would be considered a net zero technology. On-farm generation of green hydrogen via an electrolyser may be possible should sufficient renewable electricity be available as a power source.
However, due to lack of an established H2 fuel infrastructure and high production costs, there is no guarantee that green H2 fuel will become price competitive with bioCNG pre-2030, despite recent ICE development. Future use of H2 fuels in adapted ICEs could facilitate adoption of systems such as H2 fuel cells. Replacement of the ICE on farms with H2 fuel cells is unlikely before 2050 - due to rural supply limitations and also the extended life cycle of farm tractors and other machines.
In summary, biomethane provides the best ‘here and now’ option for rapid decarbonisation of farm vehicles. BEVs powered by renewable electricity offer a net zero technology option for smaller farm vehicles, while green hydrogen provides a longer term option for larger farm vehicles. For more information on fuel options for the future visit the ‘Decarbonising Farm Vehicles and Future Fuels’ sector paper. There will also be an agricultural theme at the 2023 Cenex LCV event taking place in September, which will include speakers from the agricultural industry including Sarra Manda from Small Robot Company and Richard Gueterbock from Foodchains and co-editor of the RASE Farm of the Future report.