As the national conversation around clean energy continues to intensify, the electrification of school bus fleets is frequently cited as a way for districts to cut emissions in their communities. But this strategy fails to account for the carbon emissions that are produced in the generation and distribution of the electricity that powers these buses.
Measuring the carbon intensity of an energy source helps to capture emissions across the full lifecycle of a vehicle — and reveals the surprising truth that conventional propane autogas is often a cleaner choice for school transportation than grid electricity in most states.
Carbon intensity is the total carbon emissions embodied in an energy carrier (such as electricity or propane autogas) from the source to the point of use. It’s typically expressed as grams of equivalent carbon dioxide per megajoule. For example, the carbon intensity of grid electricity for residential usage averages 139 gCO2eq/MJ on a national basis. This accounts for the extraction, generation, transmission, and distribution of the electricity stored in the bus’s battery. Electricity is not naturally occurring, so it must be produced using other resources. In fact, 60 percent of electricity in the United States is sourced from coal or natural gas, per the Environmental Protection Agency.
But even source emissions account for only about 10 percent of the total carbon intensity of the electric grid; more than 75 percent of its carbon intensity comes from the generation and transmission, where transformers step up the voltage for transmission to charging stations. According to the U.S. Energy Information Administration, more than 60 percent of the energy used for electricity generation is lost in conversion, and it continues to lose an additional 2–5 percent as it travels on transmission lines. The costs of these losses must be recouped from customers of the grid via fluctuating utility rates.
Of course, the energy efficiency of the electric grid varies by state. While several progressive states have lowered the carbon intensity of their grid with investments in renewable source energies like wind, solar, and hydropower, the majority of states still rely heavily on fossil fuels to power their grid and can have carbon intensity scores as high as 257.8 gCO2eq/MJ (Kentucky), 276.9 gCO2eq/MJ (West Virginia) or 286.7 gCO2eq/MJ (Wyoming).
Meanwhile, the carbon intensity of propane autogas used to fuel propane school buses — accounting for the extraction, refinement, and transportation of the energy — is relatively consistent at a national average of 80 gCO2eq/MJ. And with the emergence of renewable propane, this carbon intensity score can be further reduced as low as 20.5 gCO2eq/MJ. Renewable propane is chemically identical to conventional propane but made from renewable feedstocks, plant oils, animal fats, or used cooking oil. It can be blended with conventional propane to further reduce the carbon intensity of this already low-carbon energy.
So what does this mean for school districts? It means that electric school buses are certainly not “emissions-free” as advertised. The elimination of tailpipe emissions that electric school buses promise are simply traded downstream for often staggering source energy emissions – with the added burden for districts of steep acquisition and infrastructure costs, reduced range, and less up time to boot.
For most states with an electric grid powered primarily by fossil fuels, conventional propane buses actually have a lower carbon intensity over the course of their lifecycle than electric buses. Propane school buses also offer a lower purchase price, lower infrastructure costs, and greater range, even in adverse weather conditions and on long regional routes.
Far from the magic bullet they’ve been made out to be, the environmental, financial and operational shortcomings of electric vehicles are becoming more apparent on a daily basis. But converting school transportation fleets to low carbon energy is still an important milestone in our country’s path to sustainability.
Propane school buses offer a viable alternative route to reducing emissions while fulfilling the most essential obligation of a school district: getting kids to and from school safely and reliably every day.
Learn more about how propane school buses can help districts excel at both their roles and their environmental commitments at betterourbuses.com.
