The Role of Renewable Diesel
By: Chandu Visweswariah
Executive Summary
The dire, urgent and existential climate crisis we face is well-understood, with a concomitant desire to reduce Greenhouse Gas (GHG) emissions from transportation.
California has replaced nearly 65% of its diesel consumption with Renewable Diesel (RD). UPS has been transitioning a significant share of its nationwide fleet to RD. New York City now uses RD for 12,000 municipal trucks. Westchester County airport and the Village of Tuckahoe are converting to RD. So, what exactly is RD? How much does it reduce GHG emissions? When and where is RD recommended?
Here are the short answers:
Q: So, what exactly is RD?
A: RD is a drop-in replacement for diesel, but it is not a fossil fuel. It is made from vegetable oils, animal fats and waste oil by a process called hydrotreating. It is commercially available, albeit at a premium of $0.20 per gallon (the latest January 2025 data shows RD on par with regular diesel[1]). Unlike biodiesel, it can be freely blended with regular (petroleum) diesel in any proportion, up to 100%.
Q: How much does it “effectively” reduce emissions?
A: When RD is burned, it produces Greenhouse Gases (GHGs) about as much as regular diesel. However, because it comes from plant-based sources, credit is given for the CO2 absorbed when it was a plant in its past life. Taking into account lifecycle calculations in an accepted accounting methodology, RD “effectively” reduces GHG emissions by about 68% compared to fossil diesel.
Q: When and where is RD recommended?
A: We see RD as a stopgap fueling solution, when a diesel vehicle simply cannot be replaced with an electric equivalent. In situations where a diesel vehicle is in good shape, has significant remaining useful life, or where the electric equivalent is not available or practical, switching to RD will make a significant dent in effective GHG emissions for the remaining (hopefully short) life of the diesel vehicle. However, in all circumstances, we do not recommend purchasing new diesel vehicles. And since there is no analog of RD for gasoline, we recommend that gasoline vehicles (including snowplows and school buses) be replaced as soon as possible with electric vehicles.
Read on to understand the rationale behind our recommendations.
Introduction to Renewable Diesel
RD is made from vegetable oils (canola, distillers’ corn oil, cotton-seed oil, palm oil and soybean oil), animal fats (poultry fat, tallow from beef and white grease from pork) and waste oils (yellow grease and used cooking oil). The process involves treating the oil at high pressure with hydrogen in the presence of a catalyst, called hydrotreating, followed by separation of the useful diesel, called fractionation. The resulting diesel meets all the requirements for diesel internal combustion engines and can be blended with regular diesel in any proportion.
Analysis of Emissions
The figure below summarizes GHG emissions from driving a Class 8 semi-truck 1,000 miles.
The calculations supporting these numbers are included below in Appendix A. A few important notes:
- “Grid electricity” implies an electric truck charged in Westchester County, New York using regular grid power. You can mimic the calculations in the Appendix for your zip code, or contact the author if you need help.
- “2030 grid electricity” assumes that New York State meets its goal of 70% clean power in the grid by 2030 and again assumes charging in Westchester County.
- “NYPA power” means an electric vehicle of a public entity (school or municipal government) that gets its power from New York Power Authority (NYPA), a utility that provides electricity to public entities in New York. The good news is that NYPA power is already 80% clean.
- “Renewable Diesel” assumes fueling with 100% RD.
- Particulate emissions, particularly PM2.5 (Particulate Matter 2.5 microns or less in diameter), which can cause severe health consequences, are emitted in the vicinity of the driving of the truck in the case of diesel and RD, but at the possibly geographically remote power plant in the case of electric alternatives.
Recommendations
Today, for public facilities, shifting vehicles from (petroleum) diesel to NYPA’s electric power will mean a reduction of emissions of 87.9%, and even shifting from RD to NYPA power will result in 58.8% lower emissions. These are both very worthwhile actions. Even in cases where NYPA power is not available, we recommend transitioning to electric vehicles because emissions will automatically reduce as the grid is cleaned up, whereas a diesel purchase will lock in emissions for 10 to 12 years.
Based on the calculations in Appendix A, our recommendations and talking points are shown below.
- The climate crisis is a dire and urgent existential threat, requiring us to decarbonize all aspects of society as rapidly as humanly possible.
- Gasoline vehicles like snowplows, gas buses and police cars should be electrified as soon as possible, resulting in a significant reduction in Greenhouse Gases (GHGs). There is no equivalent of RD for gasoline, so municipal governments and school districts should never buy another gasoline vehicle. The required capital investments in EVs and chargers are to be weighed against monthly savings in maintenance and fuel costs. In most cases, the financial case can be made taking into account the Total Cost of Ownership (TCO) over the lifetime of the vehicle.
- Diesel vehicles should also be electrified as soon as possible. Municipal governments and schools should never buy another diesel vehicle. Again, higher up-front costs are amortized over the life of the vehicle against lower fuel and maintenance costs.
- If replacing an existing diesel vehicle with an electric one is not feasible for whatever reason, it should be fueled for the rest of its (hopefully short) life with RD to reduce its net GHG impact. This fueling choice can be achieved easily and without additional capital expense, though at a slightly higher price per gallon. This action represents low-hanging fruit that should be harvested at once.
Appendix A: Emissions Calculations
This Appendix compares Greenhouse Gas (GHG) emissions of diesel, renewable diesel and electric class 8 trucks.
Diesel GHG Emissions for Driving 1,000 Miles
Average fuel efficiency of a class 8 diesel semi-truck = 5.7 miles per gallon[2]
Number of gallons of diesel required to drive 1,000 miles = 1,000 / 5.7 = 175.44
Note that mining, refining and transporting fossil fuels causes a 30% fossil fuel overhead[3]
Effective number of gallons required to drive 1,000 miles = 175.44 * 1.3 = 228.1
GHG emissions = 228.1 gallons x 22.38 pounds of CO2e/gallon / 2204.62 pounds per ton
= 2.32 metric tons
Electric GHG Emissions from Grid Power for Driving 1,000 Miles
Average electricity needed to drive a class 8 semi-truck 1 mile = less than 2 kWh[4]
To be conservative, 25% average uplift due to cold weather during 3 months of the year
= ( 2 * 9 + 2.5 * 3 ) / 12 = 2.125 kWh
Electricity needed to drive 1,000 miles = 2,125 kWh = 2.125 MWh
Electricity overhead due to transmission/distribution losses = 4.2%[5]
Effective electricity needed to drive 1,000 miles = 2.125 * 1.042 = 2.21 MWh
eGRID 2022 carbon intensity of electricity in Westchester (NYCW) = 976.1 lbs CO2e/MWh5
Total emissions = 2.21 MWh x 976.1 lbs CO2e per MWh / 2204.62 pounds per ton
= 0.98 metric ton
An important point: as New York cleans up its grid power towards its Climate Leadership and Community Protection Act (CLCPA) goals, this number will reduce year-over-year.
Electric GHG Emissions (Grid Power After 2030) for Driving 1,000 Miles
The CLCPA has a goal of 70% clean energy by 2030[6], up from 30% now[7]. Another way of saying this is that grid power will be 30% dirty vs. 70% dirty now. Hence, assuming that CLCPA goals are met, the emissions from driving 1,000 miles = 0.98 * 30 / 70 = 0.42 metric tons.
Electric GHG Emissions from NYPA Power for Driving 1,000 Miles
Most public facilities in New York get their power from NYPA, which is more than 80% clean[8], whereas general grid energy in New York is 30% clean7. Another way of saying this is that NYPA power is 20% dirty, while grid power is 70% dirty. Hence, the emissions from driving 1,000 miles = 0.98 metric tons * 20 / 70 = 0.28 metric tons.
Renewable Diesel (RD) GHG Emissions for Driving 1,000 Miles
RD has a carbon intensity of 30 g CO2e per MJ, compared to 102 g CO2e per MJ for low-sulfur petroleum diesel[9] (or ~90 to 100 g CO2e per MJ for regular diesel[10]). Hence, the lowest possible emissions from driving 1,000 miles with RD = 2.32 * 30 / 102 = 0.68 metric tons.
[1] https://afdc.energy.gov/fuels/prices.html
[2] https://afdc.energy.gov/data
[3] https://medium.com/enrique-dans/fossil-fuels-dirty-to-use-dirty-to-transport-352ad18f440c and https://illuminem.com/illuminemvoices/energy-to-waste-fossil-fuels-dirty-secret
[4] https://www.tesla.com/semi
[5] https://www.epa.gov/system/files/documents/2025-01/egrid2023_summary_tables_rev1.xlsx
[6] https://www.nyserda.ny.gov/Impact-Renewable-Energy
[7] https://www.inspirecleanenergy.com/blog/sustainable-living/new-york-renewable-energy
[8] https://www.nypa.gov/about/the-new-york-power-authority
