Biomethane, a type of renewable natural gas, is gaining ground as a way of converting organic waste into low carbon fuel for use in vehicles. While it is unlikely to ever play a significant part in decarbonising the transport sector, capturing methane in this way could be an important contribution to reducing methane emissions from food and farm waste and to cleaning up local transport fleets
A so-called renewable natural gas, biomethane has been used in the past to create renewable electricity. But the falling costs of wind and solar power, coupled with policy changes and the simple need to find something to do with the tonnes of food and farm waste produced every day and to reduce the emissions this creates, are also boosting the profile of the fuel as a potential clean energy solution for local transport. In the US, 37 states count biomethane as an eligible source for state renewable electricity mandates, but as it becomes increasingly uncompetitive, producers are on the hunt for new markets. Marcus Gillette from the US Coalition for Renewable Natural Gas estimates that about three-fourths of biomethane in the US now goes to transportation. Use of the fuel in transport has also been given a policy push in the US thanks to changes to the federal renewable fuel standard and the introduction of low carbon fuel standards (LCFS) in a handful of states, including California. The LCFS scores fuels based on their life-cycle greenhouse gas emissions, from production through distribution to consumption, giving credit for any emissions avoided. The value of the credits is determined by market trading and is currently at about $150 per ton, says Nik Pavlenko from the International Council on Clean Transportation. Biomethane, unsurprisingly, scores much better than fossil fuels. It is rated by California’s LCFS as being about 120% less carbon intensive than fossil fuels if generated from food scraps and nearly 400% less intensive if produced from dairy cow manure. California now has 27 manure digester projects to turn waste into fuel statewide and in autumn 2017 agreed a budget of $35.2 million to fund 18 more, mostly on dairy farms. It is not only the environment that benefits. The World Resources Institute (WRI) reports that a dairy farm in the state of Indiana saves $2.5 million in fuel costs each year, while reducing methane emissions by the carbon dioxide equivalent of 24,000 tons, by powering its milk delivery trucks with biomethane made from cow manure. Private companies with large vehicle fleets, like the delivery service UPS, are also using the fuel to meet corporate sustainability goals. The WRI estimates that the 50 million tons of unused organic waste produced by the US every year are the energy-content equivalent of six billion gallons of diesel, 15% of the diesel consumed by the country’s heavy-duty trucks and buses in 2017.
What is biomethane?
“Wet” organic wastes, as they are called due to their moisture content, are typically turned into biomethane through a process known as anaerobic digestion. As the waste breaks down, it produces biogas, a mixture of carbon dioxide, methane and other trace components, which is then refined into biomethane, essentially pure methane that can be used in the same ways as conventional natural gas. It is then liquefied or compressed and used in any vehicle with a natural gas engine, most often garbage trucks, freight haulers and buses.
Biomethane is also sometimes referred to as renewable natural gas, though this term may also include renewable biomethane or power-to-methane.
What is renewable biomethane?
Biomethane is from biological origin. It is, however, also possible to create a synthetic power-to-methane clean product. It is produced by breaking down water to hydrogen through electrolysis using electricity from a renewable energy source. Carbon dioxide is then added to the hydrogen. Currently there are only pilots of power-to-methane and many question its efficiency.
Why is methane a problem?
When wet organic wastes decompose, they produce methane, a greenhouse gas that is at least 28 times as potent as carbon dioxide, although disappears faster from the atmosphere. Landfills, livestock manure and wastewater treatment facilities contribute around 30% of all US methane emissions.
Niche interest
Biomethane as a transport fuel in the EU could see a boost thanks to the recently agreed renewable energy target of 32% by 2030, including a 14% target for transport and a planned phase out of palm and soy oil by 2030 in vehicle fuel. This could create more space for biomethane, but Jori Sihvonen from the Brussels-based NGO Transport and Environment is sceptical. “Biomethane is a niche and always will be,” he says, citing the relatively limited amount of food and farm waste available as one limiting factor. For him, manure and other agricultural wastes are the best sources of biomethane in the sense of creating the fewest emissions. “Processing them…reduces methane emissions and acts as waste management,” he says. WRI concurs. The most promising biomethane projects in the US include food and yard waste diverted from landfills and livestock manure projects on farms that are not already capturing methane, it states. But these waste streams “will bring only a small amount,” says Sihvonen. A report for the European Commission, the EU executive body, by CE Delft, a consultancy, in 2016, found that if all biomethane in the EU was used in transport and none of it in electricity or heating, it would contribute to roughly 6-9% of transport energy demand. The US advocacy group Union of Concerned Scientists acknowledges in recent research the benefits of biomethane over diesel and natural gas as a fuel, but expresses concerns that it might lock in natural gas infrastructure. To avoid this, biomethane should only be used close to biogas plants connected with nearby waste water treatment, agricultural production and municipal biowaste, says Sihvonen. In other words, as a local solution for heavy duty vehicles such as rubbish trucks and in situations where biomethane will always be available to avoid any risk of refuelling happening with fossil gas or construction of new infrastructure where it is not needed, he adds. “We need to keep infrastructure on a par with what we can produce and not inflate demand,” adds Sihvonen. “One or two refining stations are not going to be a big waste of money.” But much more would be overkill in his eyes. “In passenger cars it does not really make sense to use gas,” he points out. Whether it comes from fossil or waste sources the greenhouse gas savings are relatively minor and the small amount of biogas that exists “should not be wasted” in a sector with alternatives, namely electric cars. In the long term, Sihvonen also expects heavier vehicles to be electrified. While WRI is fairly bullish about the fuel’s future, within the mentioned confines, it insists that any municipalities, states or companies considering biomethane as a climate strategy will need to be sure its use is furthering the clean energy transition. This will mean determining “the net greenhouse gas emission impacts, costs and benefits of new projects and policies on a case-by-case basis”. Biomethane is “not going to revolutionise” the transport sector, but “it has a role to play,” concludes Sihvonen.
Writers: Bentham Paulos and Philippa Nuttall Jones