Our customers frequently wonder how can the use of renewable natural gas (RNG) as a transportation fuel remove carbon from the atmosphere? This isn’t an easy concept to understand. Although hard to comprehend, using “carbon-negative” fuel is important in our business and for any group seeking to reduce its climate footprint.
Calling a fuel “carbon-negative” is a bit confusing. Referring to it as a “carbon dioxide-equivalent negative” is more accurate. This means the green-house gases (GHGs) it uses are less than the GHGs removed by its production when calculated on a carbon dioxide-equivalent basis. The carbon-negative fuel needed for this to happen has to be generated from a feedstock that is presently adding to climate change.
Renewable methane gas is the most prominent of these fuels. Methane is the primary energy bearing molecule in natural gas. It comes from the earth’s crust and is known as a “fossil” fuel. But renewable methane, what we will call renewable natural gas comes from a variety of sources including society’s management of “waste” organic material. Each year, people dispose of billions of tons of sewage, discarded food, grass and tree clippings, agricultural wastewater, dead and dying trees and other organic feedstocks that produce millions of metric tons of methane, carbon dioxide (CO2) and other climate-altering gases.
When the methane from these renewable resources goes into the atmosphere (known as “fugitive” methane), it’s a much more powerful climate altering gas than is carbon dioxide, particularly in the short term. Methane only exists in the atmosphere for 10-20 years before it breaks down into molecules of CO2 and water. But during that initial phase, methane is far more efficient and effective at trapping heat than is CO2. The measurement of the efficiency of a molecule to trap heat is call Global Warming Potential (GWP). The yardstick for GWP is carbon dioxide, which has a GWP of 1. Methane, on the other hand, has a GWP of 84 for the first 20 years. This effectively means that methane is 84 times better at trapping heat in the first 20 years of its life in the atmosphere than is CO2.
This is an important concept when we focus on capturing the fugitive methane produced by landfills, sewage treatment plants, dairies, and other sources before it leaks into the air. If we can do that, then clean and supply it to vehicle users as a substitute for gasoline, diesel or even fossil natural gas, not only are the emissions of a high GWP climate pollutant being avoided, but so are the GHGs associated with the production, transportation, distribution and combustion of the replaced fossil fuel.
This life cycle is typically referred to as “well-to-wheels,” and covers every stage in the existence of the molecule or electron used to enable the motion of a vehicle. While battery electric vehicles are acclaimed as zero emissions, the well-to-wheels carbon intensity rating of electricity is not zero because some electricity is generated by coal or other fossil fuels. Even in California where the power mix includes an increasing amount of renewable energy sources, the carbon intensity is 16.3 gCO2e /MJ
Fuels that have a carbon intensity (CI) below a pre-determined amount for that year generate credits. Fuels whose CI value is greater than that amount generate deficits. RNG from dairies generates money for farmers, fleets and fuel providers and drastically lowers green-house gas (GHG) emissions. One heavy-duty truck fueled with dairy biogas offsets the carbon emission from 2.5 diesel trucks. Carbon-negative RNG is valuable for this reason.
The process of acquiring RNG and determining its value from an emissions and monetary perspective appears to be difficult. But experts can walk any fleet manager or sustainability officer through a climate action plan focused on this carbon-negative fuel.
Feel free to contact me if you operate a fleet of natural gas vehicles and you would prefer them to be fueled with cleaner, low carbon RNG and I’ll get you set up. If you own a fleet of diesel-fueled vehicles and would like to drastically reduce the air quality impact and climate footprint of your operation, let me know. The supply of RNG is growing quickly, and our portfolio of RNG is expanding. We are ready, willing and able to help any fleet interested in using this important renewable fuel.