Within the debate around climate change, renewable energy sources (RES) hold a place of choice, and some of them come easily into our minds while others take more time to do so. Next to solar & wind, biomethane is shy, often classified as “other renewable power”. However, it is promised a bright future as solar and wind have shown their limits in fall 2021, being partially responsible for the increase of gas prices in Europe 
More than ever, our growing dependence on intermittent energy sources make it crucial to diversify the energy mix. It should be noted that even though Europe is moving towards a system that deeply relies on electricity as an energy carrier, many industries such as iron or cement making are not yet ready to be powered by electricity, hence relying heavily on fossil fuels. In opposition to other RES, biomethane shares almost all its characteristics with natural gas, making it interchangeable with it and suitable for industry applications, while using the existing gas transmission network. The number of biomethane plants in Europe increased by 51% between 2018 and 2021 , which means that despite its timidity, biogas is actually making its way. As a matter of fact, Total Energies bought the French leader in methanation Fonroche Biogaz  and is building its first methanation unit  in the United States for a dairy farm (with a production capacity reaching 40 GWh per year - to be operational by 2022).
How does it work ?
Biogas is obtained from the anaerobic digestion (microorganism breakdown of organic matter in a closed space without oxygen) of waste. Farm waste is usually poultry, pigs, cattle and sheeps as well as crops, and household’s food waste. To another extent, biogas can also be obtained from the waste water of certain industries (ie. beverage, food and paper) and from burning municipal waste . This biogas is then upgraded to biomethane, which is almost chemically identical to natural gas, and therefore suitable for gas distribution network injection and electric power generation. After methanation of agricultural waste, the solid substance we are left with is called “digestate” and can be used as a fertiliser after being mixed with water. The methanation process accelerates the decomposition of the organic matter, creating a carbon-stabilised fertiliser that is rich in nitrogen, one of the key elements in soil regeneration. [Figure 1]
A windfall for farmers
Methanation represents several opportunities for farmers. It allows them to produce energy for themselves but also to sell it to the grid, as prosumers. It also allows them to value their waste, making them important actors of the circular economy, another important challenge and system to embrace in order to reach the UN’s Sustainable Development Goals. On another note, the digestate obtained from the methanation process represents a local alternative to artificial fertilisers, participating in creating a sustainable agriculture.
Two different approaches, with different consequences
Biomethane can be obtained from different types of waste, and most importantly, at different scales. It can range from (1) an anaerobic digester in a local farm using its own waste and the ones from neighbouring farms in order to provide around 0.06GWh/year or less to power its activities and/or local communities, to (2) a much bigger biogas plant that receives waste from numerous farms as well as industrial waste. The latter provides a much bigger amount of energy to be sold directly to the national grid. In France, in the first quarter of 2021, a methanation plant with a power generation capacity as big as 663 GWh/year was installed .
These two approaches are different :
- In the first one, we value waste in a circular framework, reducing it as much as possible and turning it into a useful green energy, hence participating in decarbonizing our energy mix.
- In the second one, although participating in decarbonizing our energy mix at a larger scale, waste is now considered as a commercial commodity and gains a strategic value.
If an independent methanation plant bases its business model on generating profit depending on the amount of energy sold to the grid System Operator (SO) or the utility, it will naturally try to get as much input (waste) as possible to generate economies of scale and reduce its operating costs. This can lead to unsustainable practises such as having waste be transported by oil-fueled trucks for several hundreds of kilometres, or relying on input provided by big industries that are negligent in terms of waste management. As a matter of fact, some plastic and heavy metals, most likely coming from the methanation of industry waste, have been found in some digestate spread on a field in Normandy, France . This raises an important issue: since the digestate’s composition highly depends on the inputs, the ones obtained from abusive practises can have tremendously negative consequences, namely, land pollution.
Energy crops, incidents & leaks
Crops planted solely for energy-producing purposes rather than alimentary are called energy crops. Pushing for large-scale agriculture waste methanation using them can have unexpected social consequences, something that was observed in Germany. Germany is the world’s biggest biogas producer and home to more than 10 000 anaerobic digestion plants. Within the last decade, thanks to policy incentives, it managed to considerably increase its biogas production obtained from biomass, mostly relying on energy crops. However, the dynamics in the agricultural sector started to change drastically, leading to an increase in agricultural land rental prices : growing energy maize became more profitable than growing food maize.
In 2017, one third of the maize cultivated in Germany was destined to biogas production, which forced the country to introduce a limit of 50% of maize as digester input. The limit was lowered every year to reach 44% in 2021 .
Besides the energy crop issue, the share of incidents out of the total number of methanation units in France has been increasing steadily in the last few years. Since a methane leakage rate of only 11% means no GHG saving compared to using natural gas , a lack of attention or control can lead to the whole process becoming worthless in the net-zero pathway. According to Claudia Rouaux, a French deputy of Ile-et-Vilaine, in Brittany, in 2020, only 3 controls were performed by the French Ministry of Energy Transition for a total of 39 methanation units in the department - an alarming number.
Rectifying the trajectory
As part of the quest for diversifying its energy mix and increasing its energy independence, the European Union is encouraging the development of methanation. Germany was the first country to get on board, and France is now joining its neighbour in this path.
However, the urgent need for decarbonization framed by the Paris Agreement seems to push all stakeholders into acting too quickly, leaving space for abusive practises and for things to get out of hand, at the detriment of sustainable agriculture practises.
If methanation is to become as big as what France’s expectations predict (30 TWh power capacity by 2030) , the control and inattention gap that was observed in the last few years needs to be filled immediately, in order to avoid an exponential growing number of accidents that could have terrible consequences on the land (which in the end, is used by the very same farmers who are asked to become prosumers), and paradoxically, on the atmosphere.
For now, biogas issued from anaerobic digestion should not be accounted as a key fuel to power the macro-electricity grid. As long as the security of the soil and the neighbouring communities cannot be assured, its role should be limited to being a powering fuel for off-grid or micro-grid communities, paving the way for more decentralised, local and sustainable communities.
This article is also featured on the London Journal of Energy. Future Thought Leaders is a democratic space presenting the thoughts and opinions of rising Energy & Sustainability writers, their opinions do not necessarily represent those of illuminem.
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