Georgia Tech Study Compares Electric and Diesel Delivery Trucks

October 8, 2013

Comparing life-cycle energy consumption, greenhouse gas (GHG) emissions, and total cost of ownership (TCO) of medium-duty electric and diesel urban delivery trucks for a range of drive cycles and electricity generation scenarios, a team of researchers from Georgia Tech found that all in all, the life-cycle energy use and GHG emissions of the electric truck are lower than that of the diesel truck, particularly for the frequent stop and low average speed (NYCC- and OCTA-type) drive cycles.

The study was conducted by Dong-Yeon Lee, Civil and Environmental Engineering Ph.D. student, Valerie Thomas, Anderson Interface Associate Professor of Natural Systems in the Stewart School of Industrial & Systems Engineering, and Marilyn Brown, professor in the School of Public Policy and published in the ACS journal Environmental Science & Technology.

Researchers also found that the total costs of ownership (TCO) of the electric and diesel trucks are similar. Over an array of possible conditions, the median TCO of electric trucks is 22% less than that of diesel trucks on the NYCC. However, the cost-competitiveness of the electric truck diminishes in drive cycles with higher average speed. Battery replacement along with EVSE will also greatly affect the relative TCO of the electric truck.

For both types of trucks, vehicle efficiency is important from the perspective of energy consumption, GHG emissions, and TCO over the vehicle lifetime, researchers said. The TTW [tank-to-wheels] efficiency of the truck depends strongly on the drive cycle, and the electric truck is more likely to provide higher benefits with the NYCC-style driving conditions than with the CSHVC or similar conditions. Given the same drive cycle and thus the same vehicle efficiency, the electric truck would be more attractive to fleet operators with high truck utilization (VKT [vehicle kilometers traveled] demand), of course within the electric drive range.

Battery replacement is another key factor; to maximize the benefits from electric trucks, the durability and reliability of the automotive Li-ion battery are crucial, which might be advanced with technological development. Recycling of the EV Li-ion battery could also improve life-cycle energy consumption and GHG emissions.

There is also variation by state in the electric truck's comparative energy consumption and GHG emissions. For the baseline case, recent and projected future generation mixes result in similar or less energy consumption and GHG emissions of the electric truck compared to the diesel truck in most parts of the US.

For both types of trucks, vehicle efficiency is important from the perspective of energy consumption, GHG emissions, and TCO over the vehicle lifetime, researchers stated. The TTW efficiency of the truck depends strongly on the drive cycle, and the electric truck is more likely to provide higher benefits with the NYCC-style driving conditions than with the CSHVC or similar conditions. Given the same drive cycle and thus the same vehicle efficiency, the electric truck would be more attractive to fleet operators with high truck utilization (VKT demand), of course within the electric drive.

For the study, the team used vehicle operation data from a FedEx Express parcel delivery diesel truck of GVW class 5 (16,001−19,500 lbs) and from 219 SEV Newton electric trucks in 63 cities across the U.S.

The research team calculated life-cycle energy use and GHG emissions including vehicle operation, vehicle production and end-of-life management, electric drive battery, and electric vehicle supply equipment; they also evaluated the total cost of ownership parameters with all monetary values in 2011 constant dollars.

The life-cycle energy use of the electric truck consists of three upstream components and two downstream components. The first upstream component accounts for indirect energy input for the production and distribution of power generation fuel and the construction, maintenance, decommissioning, and waste disposal of the power plant. The second upstream efficiency component is the electric power plant's generation efficiency (ηpp). Electric grid transmission and distribution efficiency (from power plants to end-use customers) is the third component.

Downstream energy use of the electric truck comprises electric drivetrain (DC−DC converter, inverter, and electric motor) efficiency and the loss in charging/ discharging.

For the diesel truck, the overall energy use is composed of upstream efficiency of diesel fuel production and vehicle operation efficiency.

Among their other findings were:

- Over the life-cycle the electric truck consumes 28% less energy (3.49 vs 4.86 MJ/ t·km) and emits 38% less GHGs (0.24 vs 0.38 kgCO2e/t·km) than the diesel truck in the baseline case for both the 2011−2012 and the 2025 projected US average electricity mix. (The difference in GHG emissions is larger than the difference in energy use due to diesel fuel's larger fuel-cycle energy use and emissions per unit VKT and payload.)

- The comparative energy consumption and GHG emissions vary depending upon the drive cycles and the electric powertrain efficiency for the baseline diesel truck efficiency case.

- For the NYCC drive cycle, for which the diesel truck achieves only 4.6 mpg (51.1 l/100 km), life-cycle energy use and GHG emissions are 39−54% and 48−61% less for the electric truck than the diesel truck, depending upon the electric powertrain efficiency.

- For the CSHVC drive cycle, for which the diesel truck achieves 8.6 mpg (27.4 l/100 km), the energy use of the electric truck is 14% and 34% less than the diesel truck for the lowest and highest electric truck efficiency, respectively.

- For the same drive cycle, the GHG emissions of the electric truck are 27% lower than the diesel truck for the lowest electric truck efficiency and 43% less for the highest. highest.

- Results vary with the carbon-intensity of regional electricity generation. For the baseline case with the 2011−2012 US electricity mix, electric trucks have an energy efficiency advantage in most parts of the U.S., with the largest advantage in the Pacific Northwest. For GHG emissions, electric vehicles have the lowest relative emissions in the Pacific Northwest, the West, and in the Northeast.

- Other than the battery replacement, TTW efficiency of both types of trucks, diesel fuel's upstream efficiency, electric grid transmission efficiency, and coal power plant generation efficiency and GHG emissions are the top five variables with the most significant influence.

- The relative TCO is most sensitive to the diesel truck's fuel consumption (or fuel economy), VKT, and diesel fuel price scenario. The NPV of TCO differential is sensitive to battery replacement, battery price, and EVSE price.

For more information visit http://www.greencarcongress.com/2013/07/gatech-20130706.html

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