Duel on the Delivery Route: Diesel vs. Electric

Recently, a team of researchers from the Georgia Institute of Technology put medium-duty electric and diesel delivery trucks to the test on three metrics: greenhouse gas emissions, energy consumption, and total cost of ownership.

The Georgia Tech research team consisted of Dong-Yeon Lee, a civil and environmental engineering Ph.D. candidate; Valerie Thomas, Anderson Interface associate professor of natural systems in the Stewart School of Industrial & Systems Engineering; and Marilyn Brown, endowed full professor in the School of Public Policy. On average, the team found that, although electric vehicles produce fewer greenhouse gas emissions and consume less energy in most U.S. states, total cost of ownership is similar, regardless of power source. However, for suburban and highway driving, the cost-competitiveness of the electric truck falls short, according to the study’s results.

The reason: “In urban areas there is a lot of stop-and-go driving,” Lee explained. “This makes both electric and diesel trucks less efficient. But, electric trucks use regenerative braking, which allows them to move more efficiently than diesel trucks in stop-and-go driving.”

Making a Solid Comparison

The Georgia Tech research team hypothesized that electric urban delivery trucks would beat their diesel counterparts in the energy consumption category. “We started with the hypothesis that electric drivetrains will perform better in terms of energy consumption for urban delivery operations that may be characterized by frequent stops,” Brown said. “We focused on urban delivery trucks, because they tend to drive a limited amount each day and return to a garage or depot at night, which makes them well suited to electric charging.”

For the electric-powered truck, the Georgia Tech team analyzed a 2011 Smith Newton model powered by a 120 kW electric motor. Those results were then compared to the analysis of a 2006 Freightliner package delivery truck with a diesel-powered Cummins engine. Both vehicles had similar gross vehicle weight (GVW), curb weight, and payload capacity. They also traveled a similar number of miles per day, at comparable speeds, making roughly the same number of stops per kilometer.

Making an apples-to-apples vehicle comparison proved to be one of the more challenging aspects of the study.

“At one point, we had data for a model-year 2006 diesel truck versus a model-year 2011 electric truck. But, that comparison didn’t sound right; it wasn’t equal, even though these trucks had the best available real-world energy consumption and emissions data. And, we had to adjust the fuel economy of the diesel truck, based on technological advances between 2006 and 2011,” Thomas said. “Not only that, payload and gross vehicle weight had to match, so that’s why we picked the smallest and lightest model of Smith Newton electric truck, to match the diesel delivery truck.”[PAGEBREAK]

Location & Application Make the Difference

When comparing the two vehicles, the study revealed that on average in the U.S. electric urban delivery trucks use about 30-percent less total energy and emit about 40-percent fewer greenhouse gases than diesel trucks, for about the same total cost, taking into account both the purchase price and the operating costs.

However, where and how the truck is used can have a major impact on the resulting costs and emissions.

“In urban situations with lots of stop-and-start driving, electric trucks are roughly 50-percent more efficient than diesel overall, making them also about 20-percent less expensive and providing greenhouse gas savings of roughly 50 percent on average, in U.S. urban areas,” Brown said. “Energy and greenhouse-gas-emissions savings depend on the source of the electricity used to charge the vehicle. We found that, in every state in the U.S., electric trucks generally provide some greenhouse-gas-emissions savings, with urban routes providing the most advantage. We found substantial greenhouse gas reductions (35 percent or more) in half the states in the U.S.”

So, while the electric delivery truck offered at least some benefits in terms of fewer emissions and reduced energy consumption, when operated in the right context, the results could be even more significant.

“One sure thing that our study could tell is that electric trucks are beneficial in terms of greenhouse gas emissions reduction and energy savings in most of the U.S. Just as conventional diesel trucks’ fuel economy varies with drive or duty cycles, so do those of the electric trucks,” Lee said. “However, the relative benefit of electric trucks over diesel counterparts could be much more significant than one might expect. If the electric truck is deployed in the right drive or duty cycle application, fleet operators could enjoy higher returns on investment, while saving energy and reducing greenhouse gas emissions.”

Calculating Total Cost of Ownership

In addition to comparing the vehicles on emissions and energy consumption, the Georgia Tech team also looked at total cost of ownership (TCO). To calculate it, the team considered a number of factors, including:

• Vehicle specifications (e.g., payload, gross vehicle weight, battery capacity, etc.).
• Daily travel demand.
• Vehicle lifecycle.
• Drive cycle.
• Purchase price.
• Maintenance costs.
• National average diesel fuel and electricity prices.
• Lithium-ion (Li-ion) battery price.
• Battery degradation rate.
• Charging equipment discount rate variation for the time/value of money.

Not accounted for were federal/state/local government incentives, financing strategies (e.g., leasing), geographical fuel price variations, or insurance fees.

“There are two key differences between electric and diesel trucks. The first is that the purchase price of an electric truck is more than the purchase price of a comparable diesel truck, while the cost of electricity to charge the electric truck is lower than the cost of diesel fuel for the diesel truck,” Lee said. “The second key difference is that electric trucks recapture energy using regenerative braking, but diesel trucks don’t; this gives electric trucks a relative advantage for urban stop-start driving.”

Where an electric truck may require a greater up-front investment, fuel savings can bring the TCO closer to that of a diesel truck.

Thomas added that another factor in an electric truck’s TCO is the potential for electric drive battery prices to change over time. “Future prices for electric trucks may vary substantially, while the prices for diesel trucks are unlikely to change much,” she said. “Battery price reduction down the road could have a large effect on the cost-competitiveness of electric trucks, while only diesel fuel prices could have a similarly large effect on the future cost-competitiveness of diesel trucks.”[PAGEBREAK]

The Results, Three Ways

The Georgia Tech research team presented the results of its study from three perspectives: cost, environment, and location.

From a cost perspective, electric and diesel delivery trucks can be expected to cost about the same.

“For urban routes with lots of stop-and-go driving, electric trucks can be cheaper overall than diesel trucks,” Brown said. “On the other hand, there are situations in which electric trucks can be more expensive than diesel, particularly with a combination of factors: if the truck will be used in suburban and highway settings without a lot of stops and starts, if the battery needs to be replaced earlier than expected, if more expensive charging equipment is purchased, and if the truck is not used very much.”

From an environmental perspective, electric urban delivery trucks use less total energy and emit fewer greenhouse gases than diesel trucks.

“Generally, the environmental and cost benefits work together. In urban driving, electric vehicles are markedly more efficient than diesel; this results in less energy use, less greenhouse gas emissions, and lower costs on urban routes,” Lee said. “There are also advantages to electric in the suburban-highway routes, but the differences are less pronounced.”

And, finally, the study underscored that location matters. “Where electricity is generated with lower greenhouse gas emissions, electric trucks will be responsible for fewer emissions,” Thomas said. “But, even in areas where fossil fuels dominate power production, electric trucks in urban areas can be more efficient and have lower emissions than diesel.”

While the team’s hypothesis that electric delivery trucks would fare better on energy consumption in urban settings with frequent stops proved true, there were, nonetheless, a few surprises at the conclusion of the study.

“We were actually a little bit surprised that 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,” Brown said. “What we found is that, particularly in urban settings and in states with relatively low greenhouse gas emissions from electricity, electric delivery trucks both save money and have environmental benefits.”

Thomas concluded that the key to determining whether to invest in electric or diesel is to know the fleet’s routes. “Despite all the uncertainties, if fleet operators know what type of drive cycle their trucks serve, they will know if they are likely to get substantial benefits from adopting electric trucks,” she said.