What’s up with RNG (Renewable Natural Gas) and other fossil gas alternatives?

Alan Journet, Co-facilitator, Southern Oregon Climate Action Now
April 2021 – updated June 2022

After years of persuading us that Methane (Natural) Gas is ‘the clean fossil fuel,’ the gas companies have come up with a new campaign.  This campaign is designed to convince us that they have a new improved replacement for natural gas: just as the misnomer for fossil gas is ‘natural’ gas, creating the impression of a benign, even healthful fuel, so the new terms ‘Renewable Natural Gas’ and Green Hydrogen create the impression of a fuel that is environmentally benign, or even healthful. They are, however, potentially more threatening!

Note that this discussion is not about CNG (Compressed Natural Gas) used as a transportation fuel and for other purposes. CNG is simply gas (whether shale-fracked fossil gas or RNG / biogas) that is transported in and released from high pressure containers for combustion.  CNG suffers from all the drawbacks of the basic fossil gas or RNG that is compressed.

Fossil Gas Basics in Brief:

1. Fossil (natural) gas is 85 – 95% methane (CH₄).
2. When combusted to generate electricity, or heat, or whatever, methane is converted to and emits water (H₂O) and the global warming gas carbon dioxide (CO₂).
3. When fossil gas is burned to generate electricity, the methane emits just over 50% of the carbon dioxide that is emitted by coal per unit of energy generated so, if assessed only in terms of combustion emissions, it appears cleaner.  However, all greenhouse gas emissions analyses require full life cycle assessment, and this is where the benefits are often reduced or disappear.
4. Methane is 86 times worse as a global warming agent than carbon dioxide on a 20-year basis and 34 times worse on a 100-year basis.
5. From extraction by fracking (hydraulic fracturing in shale deposits) through processing and transmission, leakage (fugitive emissions) occurs.
6. Because of the high Global Warming Potential of methane, only about 2.8% leakage is enough to negate the combustion benefit noted above (# 3) where burning methane emits about 50% of the carbon dioxide emitted by coal per unit of energy generated.
7. Numerous studies of leakage over the last decade reveal that this leakage is either close to that critical 2.8% value or above it, meaning fossil gas is potentially as bad as coal.

For a more complete discussion of the drawbacks to fossil (natural) gas visit: Fossil Gas – A Bridge to Nowhere.

The Fossil Gas Substitutes

Biogas: This comprises Methane emitted from the digestion / decomposition of organic (biomass) sources such as landfills, sewage treatment facilities, forest products, Confined Animal Feedlot Operation (CAFO) manure and mega-dairy manure.  There is no doubt that the methane emitted from landfills and livestock operations contributes to global warming when it reaches the atmosphere, so capturing that methane and combusting it (which emits carbon dioxide) constitutes an improvement. The two methods for producing biogas are:

Anaerobic digestion (fermentation) occurs where bacteria that exist in an oxygen-free environment break down the organic matter and release methane as a bi-product. This is parallel to what happens in the gut of cows (and other ungulates) where enteric fermentation results in their belching methane. One problem is that the natural decomposition of the organic matter used to generate the biogas could return nutrients to the soil and promote soil health.

Thermal Gasification can convert dry organic matter (wood, paper, cardboard for example) that might otherwise take many years to decompose under high temperature conditions into methane. It is a new process with limited commercial use that require substantial energy.   The process creates methane where this otherwise would not occur.  The process can also be used to generate Hydrogen which has many uses and is not a greenhouse gas.

One issue with the biogas, especially the thermal gasification process, is the energy required to produce the product. If this is provided by genuine renewable energy sources, only limited emissions might result.  On the other hand, if the energy driving the process is fossil fuel energy, greenhouse gas emissions will be produced.  In assessing the merits of biogas, these emissions must be accounted and charged against the RNG produced.

Another over-arching drawback is that methane leakage from these process may be higher than that occurring during fossil gas extraction and processing.

In addition to the production emissions, once the biogas methane is inserted into pipelines, it leaks just as readily as the natural gas it replaces.

Synthetic Gas can be produced by an energy intensive process (electrolysis) that splits water (H₂O) into Hydrogen (H₂) and Oxygen (O₂). The Hydrogen can be used directly as a fuel, or then inserted into Carbon dioxide (CO₂) with Oxygen released as a by-product to produce methane (CH₄). Unfortunately, “The energy value of the hydrogen produced is about 80% of the energy used to split the water molecule…” in the first place (https://www.carboncommentary.com/blog/2017/7/5/hydrogen-made-by-the-electrolysis-of-water-is-now-cost-competitive-and-gives-us-another-building-block-for-the-low-carbon-economy).  This means using fossil fuel to generate Hydrogen releases more greenhouse gases than would be used by just using those fossil fuels directly as an energy source. To be an effective climate response, the energy used to manufacture the synthetic methane must be a renewable energy source  otherwise substantial greenhouse gas emissions will inevitably result. Using fossil fuel to generate Hydrogen would undermine or even negate subsequent transmission and combustion benefits.

Renewable Natural Gas (RNG) is biogas generated from biological materials (with plants at the base of the food chain) that previously captured carbon dioxide from our current atmosphere.  When the gas is ultimately combusted to release its energy, the CO2 recently captured is released back into the current atmosphere.  This means that the carbon dioxide released was recently extracted from the current atmosphere and is returned to it.  This is different from fossil gas and fossil fuels generally.  With fossil fuels, the carbon dioxide released when the fuel is burned was trapped from an atmosphere hundreds of millions of years ago, and is thus transferred from that atmosphere to ours.  This is the reason that RNG has been labelled a renewable energy source.  This is certainly a benefit over all fossil fuels. However, in undertaking the greenhouse gas accounting in assessing the relative benefits of RNG, we must undertake a full lifecycle analysis and include any fossil fuels used  during the production of the RNG and the emissions that result from that process and any leakage occurring during transmission.

In addition, unlike the process of fracking which results in fugitive emissions (leakage) of methane that potentially negates the combustion benefits of fossil gas versus coal and oil, the manufacture of RNG should not result in the release (leakage) of methane since it necessarily is sealed to exclude oxygen and maintain an anaerobic environment.  However, to reach an end-use the RNG must still be piped under pressure, during which leakage can and will occur.

However, despite some benefits, the concerns regarding RNG are several.

Availability:  The production of RNG relies either on the availability of an abundance of renewable energy to drive the manufacture of the gas, or an abundant supply of landfills and CAFOs to produce biogas.  While the abundant supply of renewable energy – especially during non-peak usage times, may arrive, we are not yet there.  Meanwhile, the need for abundant landfills or CAFO operations means that providing our energy need will promote either considerably increased consumption and waste production resulting in landfill proliferation or increasing meat and dairy consumption and the need for more CAFOs and mega-dairies.  Clearly, both methods of increasing Biogas RNG production are undesirable and should be avoided.

The result of these limitations is that RNG will likely be in limited supply.  Although the number of production facilities has grown three-fold over recent years, in 2020 the World Resources Institute indicated that in the foreseeable future RNG will still only supply 4 – 7% of current fossil gas usage. A 2020 Natural Resources Defense Council (NRDC) Issue Brief similarly concluded: “biogas and synthetic gas from ecologically sound sources may be able to replace only roughly 3 to 7 percent of today’s gas use, at projected costs that are many times the current price for fossil gas.” Meanwhile, in 2018 the Oregon Department of Energy  studied and reported the potential for RNG in the state. They concluded that, even with the technological maximum production, it could replace just 17.5% of then current fossil gas use.  The consequence is that over 90% of gas needs will likely still be fossil gas and means that our energy economy will continue to rely on fossil gas into that foreseeable future.  The fossil gas corporate strategy seems to involve promoting the illusion that RNG can replace a substantial proportion of our gas usage. Then, when this fails to materialize, and we have an infrastructure and end usage that relies on gas,  fracked fossil gas will be required to make up the difference. Regrettably, as we know, our timeline for action is short, requiring that we reach net zero emissions by 2050.  Fossil gas infrastructure has an anticipated lifespan of many decades.  The average age of each mile of Fossil (Natural) Gas Transmission Pipelines is 50 years while for Fossil Gas distribution pipelines, this value is 40 years (https://www.pstrust.org/wp-content/uploads/2015/12/Weimer-Old-Pipes.pdf).  Meanwhile, Enbridge claims pipelines have an indefinite lifespan (https://www.enbridge.com/stories/2016/september/line-5-segment-well-built-well-maintained-pipeline). The result is that the strategy adopted by California, Washington and, apparently, Oregon of promoting RNG means either we are locked into the continued use of fracked fossil gas beyond that net zero deadline, making achievement of that requirement an impossibility or the gas utilities will find themselves with pipelines as useless stranded assets as we transition completely away from their product.

Cost:  It is critical to assess the economics of RNG.  Reports suggest that  the current cost of RNG is between two and five times that of fossil gas. In an RNG energy economy, monthly domestic gas bills could easily climb fivefold promoting a switch to less expensive energy sources. Given this likely outcome, it makes little sense to promote RNG rather than simply focus future energy strategies on the inexpensive and genuinely renewable sources.

Carbon Intensity: On the positive side of the leger, it is suggested  that RNG will likely reduce greenhouse gas emissions somewhat compared to fossil gas with a reduction to 55  – 60% when sourced from a landfill or sewage treatment plant.  However, given that RNG will not replace fossil gas, merely a small proportion of it, we will have to continue using fossil fuel to make up the difference and will continue with the current fossil gas economy.  There may be specific situations where RNG is beneficial, such as industrial processes where no net zero emissions option is currently available.  However, generating RNG to provide a small percentage replacement of fossil gas in pipelines is unlikely to provide much, if any, benefit.

Industry Obfuscation:  In promoting RNG, the gas industry frequently implies that fossil gas is being replaced by, or can be replaced by, RNG. However, as discussed above, the replacement is anticipated to cover only a very small proportion of the fossil gas.  This reflects the consistent focus on obfuscation that fossil gas companies have exhibited.  For example, when promoting pipelines (such as Pembina’s promoting the Pacific Connector Pipeline and Jordan Cove LNG export facility) they claim that the combustion of natural gas is cleaner (i.e., producing less carbon dioxide) than coal.  While correct, this totally ignores the fugitive emissions of methane from extraction through delivery to the end-use of the gas discussed above.

For an extended discussion of these drawbacks, please visit: The Four Fatal Flaws of Renewable Natural Gas and The Smoke and Mirrors Defense of RNG. Meanwhile, a recent 2020 report revealed: “RNG is not inherently climate friendly. Based on consideration of both the source of methane used to produce RNG and the likely alternative fate of that methane, and using reasonable assumptions about likely system methane leakage, it is unlikely that an RNG system could deliver GHG negative, or even zero GHG, energy at scale.” Note that this assessment does not account for emissions resulting from the RNG production.

Although RNG may be useful in some limited situations, the evidence suggests that it is not a Renewable energy source like wind, solar, geothermal and wave sources or even hydroelectric energy. In a world seeking to reduce greenhouse gas emissions, our better strategy is to electrify as much as possible.  This is because even though electricity may current be generated in part from fossil fuels, the direction we are heading is to convert that generation to clean renewable energy sources. Thus, ultimately, electricity will be clean.  For example, Oregon’s 2021 HB 2021 decrees that Oregon’s retail electricity supply shall be generated 100% from clean energy sources by 2040.   The 2022 report from the United Nations Environment program – Stockholm + 50, furthermore, promotes the complete phase-out of fossil fuels.  Clearly, we should not be extending our dependence on fossil fuels such as methane gas by replacing a small percentage of it in our pipelines with a substitute that ultimately will require that we continue to use that fossil fuel.