Calculating and comparing air emissions from electric vehicles (EVs) and gasoline- or diesel-fueled vehicles is a complicated endeavor. While EVs, including hybrids, produce lower tailpipe emissions than conventional vehicles do—and zero tailpipe emissions when running only on electricity—tailpipe emissions are only one factor to consider in a vehicle’s lifecycle emissions.

Gasoline and electricity fuel pathways also have upstream emissions to consider, which include extracting, refining, producing, and transporting the fuel. Estimating cradle-to-grave emissions must account for both fuel-cycle emissions (also known as “well to wheels”) and vehicle-cycle emissions (material and vehicle production, as well as end-of-life considerations). The combined emissions from vehicle and fuel production through vehicle decommissioning (that is, recycling or scrapping) are referred to as lifecycle or cradle-to-grave emissions.

Many researchers have conducted studies to quantify and compare lifecycle emissions, including experts at U.S. Department of Energy labs. Among the findings, as any knowledgeable power industry observer might expect, is that the source of electricity has a significant effect on the emissions of an EV.

The Alternative Fuels Data Center (AFDC), a resource of the U.S. Department of Energy’s Vehicle Technologies Office, provides an online tool for estimating CO2 emissions from EVs based on charging power sources, using assumptions from 2021 data in the U.S. Energy Information Administration’s (EIA’s) database. The tool says if, for example, an EV is charged in Wyoming, where the electric grid was powered more than 75% by coal, according to the 2021 EIA estimates, the annual CO2 emissions from an all-electric vehicle would be about 5,986 pounds of CO2 equivalent, more than double the national average of 2,817 pounds of CO2 equivalent. That’s because coal only accounts for about 22.28% of the electric supply nationally.

Furthermore, if the same EV was charged in Washington state, where nearly two-thirds of electricity is supplied by hydropower, and wind and nuclear (another carbon-free resource) supply 8.54% and 7.82%, respectively, the CO2 equivalent emissions would be only 705 pounds annually. Yet, no matter the fuel being used to generate electricity, EVs emit significantly less annual carbon emissions than gasoline-fueled vehicles, which release 12,594 pounds of CO2 equivalent emissions, according to the AFDC calculator.

One fuel source that may not immediately come to mind when thinking about charging EVs is propane. However, there are innovative vehicle-charging options available using propane, and it is a relatively low-carbon fuel source, especially when “renewable propane” is available.

Jim Bunsey, director of commercial business development with the Propane Education & Research Council (PERC), shared details on a portable propane-fueled EV charging unit that is available today. “It takes up about a parking space,” he explained as a guest on The POWER Podcast. “It’s a trailer that weighs under 10,000 pounds—so, it’s a non-commercial load—and they have about 100 to 120 gallons of storage onboard.”

During the Advanced Clean Transportation Expo (ACT Expo) held May 1–4, 2023, in Anaheim, California, PERC put the portable charging station to the test. The expo included a “Ride & Drive Event,” which allowed attendees to take dozens of the latest advanced clean vehicles for a test run. What the event needed was a way to charge the electric vehicles during the show. The portable trailer fit the bill.

“Now, the fun part is, we hooked up with a large propane retailer in the area, and they actually had renewable propane available to us. So, we were charging the electric vehicles—a zero-emission tailpipe—we were charging them with a carbon-intensity score, with a blend that we had, less than 20,” Bunsey said. He noted that the carbon-intensity score for the California grid is right around 79 to 80, and that non-renewable domestic propane typically runs around 79 to 80 as well. “So, we’re equal to the grid in that area—depends on how we look at carbon intensities—but since we had the blends that were available to us, we were charging with a carbon intensity of 20, which was amazing that we were there. So, it was very successful,” he said.

Bunsey said the original equipment manufacturers (OEMs) demonstrating their vehicles at the ACT Expo became very excited about the possibility of charging vehicles with propane. “We were charging these over-the-road electric vehicles at 700 volts with nice, quiet, clean-burning propane that was reliable, and it opened the OEM’s eyes. They’re like, ‘Hey, we want to do this.’ And luckily, we’re starting to pair with OEMs to help them electrify the future,” said Bunsey.

Using the AFDC calculator, annual CO2 equivalent emissions for an all-electric vehicle charged in California was 1,473 pounds in 2021. If we assume renewable propane offers a carbon intensity of about one-quarter that of the California grid, the CO2 equivalent emissions using renewable propane would even be close to half what was estimated earlier in the Washington state example.

For fleet owners that are just getting started with EVs and may not have the infrastructure and transformers in place to charge at 700 V, the propane-fueled portable trailers could make sense. The systems could be scaled up as fleets expand, then, once permanent, grid-connected charging stations are installed, propane could be phased out or continue to act as a backup. It frankly provides a lot of options.

To hear the full interview with Bunsey, which contains more about the benefits of propane in other power generation and battery charging applications, listen to The POWER Podcast. Click on the SoundCloud player below to listen in your browser now or use the following links to reach the show page on your favorite podcast platform:

For more power podcasts, visit The POWER Podcast archives.

Aaron Larson is POWER’s executive editor (@AaronL_Power, @POWERmagazine).