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In recent years, renewable energy alternatives have seen increased adoption to minimize energy sector emissions, with significant increases beginning in the early 2000s. One renewable energy source gaining increasing attention is Renewable Natural Gas (RNG). RNG is a green molecule that substitutes traditional natural gas and that harnesses pre existing emissions from the decomposition of organic material to create biomethane. This green molecule alternative has the same functionality as natural gas, such as thermal applications, electricity generation, and compressed (CNG) / liquid (LNG) vehicle fuels.
When burned, RNG emits CO2, similarly to conventional natural gas. The first step to producing RNG is transforming organic material into biogas. This can be accomplished via thermochemical processes such as gasification, where heat and oxygen convert organic material into biogas (Chan et al., 2021). Another way to produce biogas is anaerobic digestion, where microorganisms decompose organic matter in the absence of oxygen. Various sources of organic material can be used for biogas production, including landfills, livestock refuse, food / agricultural waste, forest residue and wastewater treatment plants.
Once the raw biogas has been produced, it contains approximately 45-65 percent methane, along with additional gasses and contaminants (US EPA, 2022). In order to create RNG, the biogas must be “upgraded” by removing moisture, hydrogen sulfides, CO2, and other trace contaminants to reach a methane content of at least 90 percent, with pipeline-quality RNG ranging from 96-98 percent methane (US EPA, 2022).
The adage “one man’s trash is another man's treasure” perfectly symbolizes RNG production, as previously disregarded waste streams now have increasing economic value. This new market will bring economic benefits to local communities where RNG projects are implemented, as processing and fueling infrastructure construction will generate jobs and economic growth (US EPA, 2022).
The ability to convert GHG-emitting waste streams into a renewable fuel source has multiple environmental benefits. Capturing and recovering methane emissions that would have otherwise been released into the atmosphere helps to slow short-term warming, as methane has an atmospheric lifespan of approximately 12 years and a warming potential 25 times that of CO2 (US EPA, 2022). In addition to warming mitigation, RNG uses pre existing methane emissions as opposed to unearthing fossil fuels, thus making RNG a low-carbon or carbon-neutral fuel source, depending on the feedstock. The figure below depicts the lifecycle emissions for multiple RNG feedstocks compared to diesel and conventional natural gas, with landfill as the most carbon-intensive feedstock and animal manure as the least intensive (Cyrs et al., 2020, p. 7). Additionally, using RNG for vehicles can improve local air quality as biomethane has been “upgraded” to remove constituents, thus reducing particulate matter and emissions of nitrogen oxides compared to traditional gasoline and diesel vehicles (US EPA, 2022).
One additional benefit of RNG is increased fuel security. The current conflict in Ukraine has unveiled global concern about energy stability, with some suggesting the answer lies with increased investment in fossil fuels. While this may alleviate current energy stressors, increased emissions from fossil fuels would continue to intensify climate change, ultimately placing further strain on energy security. With RNG, nuisance waste streams can be converted into biomethane and used in pre existing natural gas infrastructure, thus offering increased fuel diversity (US EPA, 2022). Likewise, RNG’s on-demand nature can smooth energy fluctuations associated with intermittent renewable energy such as wind and solar. These technologies could accelerate the transition to renewable energy when used in conjunction. A recent study by Gas for Climate 2050 showed that biomethane availability in the EU member states is 40 bcm (roughly 1,400 bcf) by 2030 and 151 bcm (roughly 5,300 bcf) by 2050. This is significant when compared to the EU’s total natural gas consumption of 400 bcm and even more significant when considering that 155 bcm were imported from Russia before the start of the conflict.
Of note is that ~40% of the European RNG projection comes from thermal gasification of waste organic materials, a well-known process that is only recently receiving significant investment in technological innovation and project financing, meaning that we are only scratching the surface of RNG availability. The US has fewer RNG projects than the EU (the RNG coalition tracks 276 operational projects in the US and Canada vs more than 740 operational projects in the EU) but recent activity sees the US market growing fast and is projected to double to 540 operational projects within the next 3-5 years. With the recently passed IRA, additional investment tax credits available to biomethane projects will surely further accelerate the growth of RNG in the US.
RNG is a great fuel source but is not perfect. The first potential issue is RNG leakage. Like its fossil based counterpart, RNG has a global warming potential greater than 25 times that of CO2, meaning that the infrastructure to upgrade and distribute biomethane to end users needs to be adequately monitored. Companies like Highwood Emissions offer a robust suite of software and services to help utilities and oil and gas producers in mitigating emissions of natural gas and RNG alike, while technology developers like SeekOps can fly their ultra-sensitive methane sensors over landfills and anaerobic digesters to spot potential leaks. Companies like Qube, Kuva, Entanglement, and others can help in monitoring in a continuous or near-continuous fashion the facilities producing and upgrading RNG, while companies like those we highlighted in our previous blog post on satellite emissions management can provide high level system-wide leak detection services.
Another element to consider in RNG is the cost compared to fossil fuel alternatives. In 2019, the average cost across all feedstocks to produce one million Btu of RNG was between $7 - $20, compared to $3 per million Btu for wholesale natural gas (Feinstein & de Place, 2021)(Cyrs et al., 2020, p. 31). This cost differential can make wide-scale adoption of RNG difficult, especially as a function of heating and cooking appliances for homes and businesses. As the number of RNG projects increases, RNG price is going to decrease since most of the costs associated with RNG production come from the capex of building the gas production, upgrading and grid injection systems, for which the experience of suppliers, engineering firms and project developers is limited to a few hundred sites in the US.
The third limitation of RNG is availability. Current projections from American Gas Foundation indicate that by 2040, RNG production will be approximately 1,100 - 2,200 BTF, which accounts for 6-11 percent of 2018’s natural gas consumption, as shown in the figure below (Cyrs et al., 2020, p. 8). However as new sources of sustainable feedstocks get incorporated in co-digestion applications in anaerobic digesters or in thermal gasification projects, the availability of RNG is going to increase and to displace a meaningful portion of today’s natural gas consumption, offering a strong decarbonization potential and the ability to leverage existing natural gas infrastructure. In addition, new technologies that are just now seeing the light of day, such as Cemvita’s revolutionary CO2 bio-methanation process, could pave the way for a future where green molecules such as RNG become the dominant gas flowing through the pipes that bring us heat and energy every day.
A special thank you to MBA Associate, Rex Anderson, for all of his help in writing this article.
