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Georgia Tech study finds MD electric urban delivery trucks have cost advantages over diesel in some conditions; relative benefits depend on numerous factors
26 September 2013
Researchers at Georgia Tech have compared medium-duty (MD) electric and diesel urban delivery trucks in terms of life-cycle energy consumption, greenhouse gas (GHG) emissions, and total cost of ownership (TCO). One surprise among their findings was that the electric truck had cost advantages over the diesel vehicle under some conditions. The team had expected that electric truck costs would always be higher, especially since the purchase price of the electric truck studied was higher than that of the diesel truck.
In a paper published in the ACS journal Environmental Science & Technology, they report that the relative benefits of electric trucks depend heavily on vehicle efficiency associated with drive cycle; diesel fuel price; travel demand; electric drive battery replacement and price; electricity generation and transmission efficiency; electric truck recharging infrastructure; and purchase price.
Urban delivery trucks may be a suitable application for electrification. These medium-duty postal and parcel delivery trucks operate in an urban environment in which a significant portion of their trip time is spent idling, resulting in low fuel economy. Urban delivery trucks have low average driving speed, and electric motors provide higher efficiency at low speeds. Also, frequent deceleration and stops in urban driving are well suited to utilization of regenerative braking. And since these trucks typically operate on almost the same route every day and return to a company garage at the end of every operation, systematic central recharging is feasible.
Although electric vehicles have been identified as a way to increase energy security and reduce air pollution, fleet operators may not see electric trucks as an attractive alternative to conventional internal combustion engine (ICE) trucks if electric trucks are not cost-effective. Some recent studies have concluded that electric trucks may not yet be cost-competitive, mostly depending upon vehicle utilization level, purchase price, diesel fuel price, and diesel truck fuel economy.
The relative merits of electric and diesel trucks also depend on the life-cycle environmental impacts. Although electric trucks do not produce tail-pipe emissions, greenhouse gas (GHG) emissions from electricity generation could be substantial. And even though electric trucks may have greater tank-to-wheels (TTW) efficiency than ICE trucks in city delivery operation, the overall energy efficiency of electric trucks depends on life-cycle energy use including upstream electricity generation and transmission efficiency.
Here we explore the GHG emissions, energy saving potential, and cost-effectiveness of electric urban delivery trucks over their lifetime for urban delivery operation. The objective is to provide answers and insights to the following questions: Which type of truck, under what conditions, consumes more energy? Which emits more GHGs? Is the electric truck cost-effective in comparison with the diesel truck? Which factors are the most and least significant when evaluating the total cost of ownership? This analysis can provide a basis for medium-duty fleet operators and policy makers to better understand the promises and limitations of electric urban delivery trucks.—Lee et al.
The comparison involved a 2011 Smith Newton electric truck powered by a 120 kW electric motor, and a 2006 Freightliner truck powered by a Cummins diesel engine. The two trucks had approximately the same gross vehicle weight, curb weight and payload. The comparison controlled for improvements in diesel efficiency between 2006 and 2011.
The researchers 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 (EVSE). equipment)./p>
The total cost of ownership (TCO) for electric and diesel trucks comprised purchase cost, maintenance cost, fuel or electricity cost, EVSE cost, and battery cost.. They excluded other factors such as insurance, purchase incentives, tax credits, or penalties. They evaluated the total cost of ownership parameters with all monetary values in 2011 constant dollars.
The research team took into account the sources of electricity used to charge the electric vehicles in evaluating greenhouse gas emissions. Electricity produced from hydroelectric sources—more common in the northwest United States—significantly reduced total greenhouse gas emissions for electric vehicles operated there. Vehicles operated in states heavily dependent on coal for producing electricity showed higher emissions.
Very broadly, they found that:
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.
For a drive cycle with frequent stops and low average speed such as the New York City Cycle (NYCC), electric trucks emit 42–61% less GHGs and consume 32–54% less energy than diesel trucks, depending upon vehicle efficiency cases. Over an array of possible conditions, the median TCO of electric trucks is 22% less than that of diesel trucks on the NYCC.
For a drive cycle with less frequent stops and high average speed such as the City–Suburban Heavy Vehicle Cycle (CSHVC), electric trucks emit 19–43% less GHGs and consume 5–34% less energy, but cost 1% more than diesel counterparts.
Considering current and projected US regional electricity generation mixes, for the baseline case, the energy use and GHG emissions ratios of electric to diesel trucks range from 48 to 82% and 25 to 89%, respectively.
Whether the battery is replaced or not over the vehicle lifetime makes a big difference in the relative diesel versus electric truck energy use and GHG emissions: 82% for energy use and 34% for GHG emissions. Other than the battery replacement, the top five variables with the most significant influence are: TTW efficiency of both types of trucks; diesel fuel’s upstream efficiency; electric grid transmission efficiency; coal power plant generation efficiency; and GHG emissions.
The total costs of ownership (TCO) of the electric and diesel trucks are similar. The electric truck is relatively more cost-effective on the NYCC and when VKT demand is higher. However, the cost-competitiveness of the electric truck diminishes in drive cycles with higher average speed.
Wild cards in the study included the future costs of both diesel fuel and electricity, and the potential cost of replacing an electric truck’s battery pack if it has a shorter-than-expected lifetime. Lithium-ion battery packs are expected to last the lifetime of the trucks, as much as 150,000 miles for the drive cycles tested.
Over the life of the truck, there are many situations in which the total cost of operating an electric vehicle is less than operating a diesel vehicle. Our expectation was that the electric vehicle would provide environmental benefits, but at a cost. We found that particularly in urban settings and in locations with relatively low greenhouse gas emissions from electricity, electric delivery trucks both save money and have environmental benefits.—Marilyn Brown, co-author and a professor in Georgia Tech’s School of Public Policy
Dong-Yeon Lee, Valerie M. Thomas and Marilyn A. Brown (2013) “Electric Urban Delivery Trucks: Energy Use, Greenhouse Gas Emissions, and Cost Effectiveness” Environmental Science and Technology, 47 (14): 8022-8030, doi: 10.1021/es400179w
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