For fleets expecting improved total cost of ownership (TCO) when purchasing an electric truck, a new study suggests that may not always be the case. Researchers at the Georgia Institute of Technology found that while electric trucks provide a definitive energy efficiency advantage, TCO for an electric truck vs. a diesel-powered model may not result in the price advantage fleets expect.
The study, authored by Dong-Yeon Lee, from the Georgia Tech School of Environmental Engineering, Valerie M. Thomas of the School of Industrial and Systems Engineering and School of Public Policy, and Marilyn A. Brown from the School of Public Policy, was published in Environmental Science & Technology.
Researchers tested a 2011 Smith Newton model with GVW of 7,490 lbs., curb weight of 4,260 lbs. and payload of 3,230 lbs. The truck was powered by a 120 kW electric motor traveling an average of 31 mi. per day at an average speed of 32 mph while making an average of 1.7 stops per kilometer. That was compared with a 2006 Freightliner package delivery truck with a Cummins engine with a GVW of 7,260 lbs., curb weight of 4,400 lbs. and payload of 2,860 lbs. It traveled 41 mi. daily at an average speed of 32 mph making 1.9 stops per kilometer.
Each vehicle was tested in three “drive cycles,” the New York City Cycle (NYCC), Orange County Transit Authority Bus Cycle (OCTA) and the City-Suburban Heavy Vehicle Cycle (CSHVC).
“The electric truck is relatively more cost-effective on the NYCC and when VKT (vehicle kilometers traveled) demand is higher,” the authors noted. “However, the cost-competitiveness of the electric truck is expected to diminish in drive cycles with higher average speed…furthermore, battery replacement along with EVSE (electric vehicle supply equipment – aka charging equipment) will greatly affect the relative TCO of the electric truck.”
TCO calculations included purchase cost (assumed $25,000 to $37,000 more for the electric vehicle), fuel or electricity cost, EVSE cost and battery cost. Also considered was the cost of diesel fuel, greenhouse gas emissions (GHG), energy saving potential and cost-effectiveness of the vehicles in urban delivery operation. The authors noted that to calculate the vehicle lifecycle, certain assumptions had to be made, including a mileage limit (it was assumed the vehicle had ended its useful life when it reached 150,000 mi.) and the decision to not factor in battery replacement costs on the electric vehicle. Other items excluded were insurance, purchase incentives and tax credits.
The study noted that electric truck maintenance costs are 35% lower than diesel trucks due to the lack of an engine and transmission-related maintenance. Further savings on the order of 20-30% are incurred due to longer brake pad life.
Diesel fuel costs in the study were estimated at the July 2011 price of $3.87/gal.
Based on the results, the authors determined that the electric truck consumes 28% less energy over its lifetime than a comparable diesel model and 38% less greenhouse gas emissions (GHG). These results vary based on drive cycle and the electric powertrain efficiency, the authors noted.
For example, in the NYCC example, the diesel truck averaged 4.6 mpg and had energy use ranging from 39-54% higher than its electric counterpart and GHG emissions 48-61% higher. That gap, though, closes significantly in the CSHVC drive cycle, where the diesel truck achieves 8.6 mpg and has a 14-34% range deficit in energy use and 27-43% deficit in GHG emissions.
The authors concluded that “the total cost of ownership of the electric and diesel trucks are similar.” Using regression analysis, the study noted that “relative TCO is most sensitive to the diesel truck’s fuel consumption (or fuel economy), VKT, and diesel fuel price scenario. Almost in the same degree, the [net present value] of TCO differential is sensitive to battery replacement, battery price and EVSE price.
“All in all, the lifecycle 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,” summed up the authors. “For both types of trucks, vehicle efficiency is important from the perspective of energy consumption, GHG emissions, and TCO over the vehicle lifetime. 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 demand), of course within the electric drive range.”
The full study can be purchased here for $35 for 48 hour access.