3 April 2023
Dr David Cutress: IBERS, Aberystwyth University.
- Circularising energy on farms could reduce costs and greenhouse gasses and even generate revenue, or valuable by-products
- Technologies for producing energy for circular use on farms include those which utilise ‘waste’ organic streams (waste to energy WtE) and those which use naturally available energy sources such as the wind, water flow and the sun
- Knowledge on developing technologies and implementing them on farms, along with infrastructures for valorising energy produced may vary depending on the system size and complexity
Renewable energy (RE), waste to energy (WtE) and circularity in agriculture are closely related concepts. Circularity in agriculture as discussed in previous articles, refers to closing the loop on the inputs and outputs of an agricultural system by reusing and recycling resources. It aims to minimize waste and environmental impact while maximizing efficiency and productivity. REs can play an important role in the circularity of food production as it allows farmers to generate clean energy thus reducing the need for fossil fuels which minimises the environmental impact of food production. REs can equally play roles in non-food agricultural output productivity such as pharmaceuticals and timber, via many of the same mechanisms. Anaerobic digestion (AD) and biomass combustion are a highlight of renewable energy technologies, as they allow the conversion of agricultural waste into energy.
Currently REs accounts for more than 35% of our total electricity share in the UK, with the majority generated via wind (more offshore than onshore) and solar. Whilst progress is being made to increase the capacity of RE production, it is worth considering the unpredictability of these technologies. The graph below produced by the ‘Department for Business, Energy and Industrial Strategy’ (BEIS), shows that over 4 years renewable energy generation has seen the greatest fluctuations of all energy types presented. This is due to the system being heavily influenced by weather conditions and climatic patterns. These conditions caused an 18% rise in electricity from renewables, at the end of 2022, compared to the equivalent period in 2021. This was associated with generally higher wind speeds producing more electricity in wind farms, whilst periodic heat waves can massively influence solar collection. However, there are other RE technologies which if integrated into UK infrastructure can be far less variable once optimised. Despite this, due to the complex infrastructure considerations i.e. storing and supplying energy during peak and off-peak times, these technologies are hard to implement on large scales. In current infrastructures, specific power plants exist that are only fired up to account for predicted peak time energy uses, however, certain RE systems could replicate this with specific AD/CHP timed systems or specific energy storage considerations.
Anaerobic digestion (AD) systems can convert manure, food waste and other organic materials into biogas, which can be used to generate both electricity and heat. The remaining digestate can be used as a nutrient-rich fertilizer for crops, closing the loop on nutrient cycling. Current figures suggest that AD system costs range between £500,000 and £5,000,000 depending on the size of the farm and the size of the plant required, to process the biological material available (along with other efficiency aspects). Currently, over 500 AD plants in the UK are generating approximately 3% of our total renewable energy (enough to power around 900,000 homes). The most exciting aspect of this is adding value to farm produced products while reducing farm production costs and mitigating GHG emissions.
Considering that much of our modern precision agriculture-based tools are heavily reliant on electricity, especially with increased options for electric vehicles and other general electricity needs, generating ‘free’ electricity on farms is of interest. Solar, wind and hydroelectric are the most applicable energy generating options in the UK with different potentials depending on the farm’s geographical location, specific topography and annual weather patterns. These could have sufficient scope for reducing GHG emissions associated with energy and reducing costs in high energy farming systems like dairy, where it is suggested that farms can be spending between £40 - £100 per cow per year on energy (That’s an energy cost of £76 - £190 million a year in the UK alone).
Similar to AD, there is potential to use organic feedstocks directly for combustion in combined heat and power (CHP) generation to produce both usable heat and electricity (depending on the system design). The previous diagram for AD utilisation can be considered relatively equivalent to CHP and has multiple routes for circularity. In many instances, the best route to efficiently use non-wood type biomass without many hindering by-products (such as boiler damage and increased maintenance) is pre-processing with AD then burning the biogas produced in CHP systems.
This is demonstrated in the following figure where the key routes go through CHP processing, or for processing for use in gas grids, or direct gas fuel storage. Be aware that all elements labelled with an asterisk in the diagram also need to be considered as components necessary on farms, in order to utilise AD and or CHP.
Taken from the 'Sustainable energy authority of Ireland' documentation
Another targeted circular use of CHP, is the utilisation of specific biomass crops for energy production. This option for self-sufficient energy production, for farmers and the country as a whole is a growing area of interest and is now the 4th largest contributor to UK energy generation. A wealth of biomass crop options including Miscanthus grasses, have been suggested with different energy generation potentials and geographical and topographical preferences for growth. But essentially, when looking towards a sustainable farming future, these have a lot of potential as circular energy tools, for either co-localisation with crops and livestock via agroforestry practices or use in marginal land or riparian strips. Importantly, along with carbon-neutral sources of energy, biomass crops have potential in carbon sequestration due to their impact on soil carbon storage.
The production of renewable energies on-farm has some tantalising circularity considerations when we consider using ‘free’ green energy to add further circularity or sustainability on farms. For example, a recent paper from Philadelphia showed that it is possible to strip ammonia from the side streams of certain AD plants, by using energy and chemicals. This offers lower costs and lower GHG emission routes for producing cheaper fertiliser, as it was noted to use up to 15x less energy than current fertiliser production methods. Whilst these are being assessed with regards to wastewater plants, there could be future scope for powering this ‘ammonia air stripping’ process using circular energy on farms to produce circular fertilisers. There is also no reason why a single technology needs to be used alone, as often a combination of tools can work well on the same farm. Other exciting options could include farmers having more incentive to consider controlled environment agriculture, where currently the high energy demands are a downside of the system. This could facilitate farmers using renewable energy produced to grow certain crops indoors, with consistent yields and no impacts from the trends of increasingly unpredictable seasonal weather, devastating crop yields and farm economics. Furthering this, freed-up outdoor land could then be used for focused sustainable practices such as species rich grasslands, amongst others, which will likely provide landowners with increased payback from government schemes which are progressively incentivising such practices.
Risks and barriers
There are some clear benefits of circular energy being incorporated on farms, but as with most innovations, in practice, there are numerous barriers and risks to consider before diving in. One major barrier is the initial costs of the renewable generating technologies themselves. These were given rough estimates in the previous section and require careful planning and consideration of return on investment (ROI) and potentially significant bank loans to secure. There are several expert finance groups which specialise in securing bank loans for various RE agricultural applications. But aside from loans, it will be important to assess available grants funding and specific incentives being offered to farmers towards mitigating RE costs, via governments and other authorised bodies on a continuous basis.
Other specific risks and barriers with regard to WtE were discussed in detail in a cross-Europe paper, produced in 2021, and are summarised below. You may note that many of these considerations would easily be applicable to other non-WtE RE technologies.
A largescale barrier to RE use is knowledge. Renewable systems require a certain level of knowledge and planning to set up and utilise in optimal ways. Whilst expert consultants are available, these come at a cost which can impact your ROI timescale. It is possible that improving the training provisions and opportunities available, to both farmers and non-farmers alike, would encourage the development and competitivity of RE markets in the UK. Particularly as there is a wealth of permitting and permission regulations to navigate surrounding RE generation, storage and the utilisation of by-products like digestates on soils.
Other challenges might include competing for the valorisation of waste streams. For example, with biochar/composting and direct combustion of waste for energy production in power plants. Already established streams will have the benefits of historical data and firm monetary values being able to be provided for waste products. This may be appealing for valorising waste presently, but might be undervaluing waste compared to what could be achieved following on-farm investments.
Finally, many farmers and land owners would be seeking to valorise their energy production if they can produce excess to their requirement. However, in order to sell energy back to the grid there needs to be sufficient infrastructure. Not only does this require specific equipment to be installed at extra costs, it may also be unfeasible for smaller scale projects at certain geographical locations due to distance or energy transport required. Essentially changing their requirements as shown in the table below.
Renewable electricity generating opportunities often require a transformer to be added within the supply chain to supply back to the national grid. In these circumstances it is often considered that the cost of adapting the grid is not worth the energy being generated in small scale systems. As such without major overhaul of infrastructure of the national grid this may act as a discouragement to smaller RE schemes on farms. Though it is noted in review papers that such small energy generation opportunities would still be majorly beneficial for utilising the energy on-site and reducing demand on the grid overall.
There is a lot of potential for circular energy cycles within livestock systems which could make great use of current low-value waste products or naturally occurring energy sources. Utilising these in optimal ways should help to reduce the carbon footprint and ultimately costs of agricultural practices and make agriculture more resilient and sustainable moving forwards.
To increase the use of renewable energies and circularity in the agricultural sector, it is likely that grants and funding would be a good incentive. Importantly, any grants and funding should not only focus on system costs, but also on training towards designing and running such systems optimally. Whilst this will have inherent cost impacts, it could go towards reducing the time it takes achieve ROI for different systems and upskilling farmers, to improve self-sufficiency and ability to diversify. This could ultimately lead to a reduced need to subsidise food production.
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