Heavy Payloads and Commercial EV Range — a Real-World Test

In last month’s article “Understanding Effects of Payload and Towing on Commercial EV Range,” we examined how fleet operators will need to adjust duty cycles to the more limited ranges of the first wave of electric commercial vehicles. That article considered a variety of factors that will affect actual EV ranges in the real world, though much of the analysis was anecdotal.

This article will dig deeper to understand the effects of payload and other factors on EV range for a larger vehicle class in a commercial fleet duty cycle. This time, we have the benefit of telematics data and operator inputs in an actual use case.

The demo was conducted by a beverage distribution company servicing Sacramento, California. The company used a Class 6 truck with an electric drivetrain conversion from Lightning eMotors. The truck, a General Motors 6500 cab-over with a 24-foot box, was spec’d with a 160-kWh battery pack.

The truck was driven from January to May 2020 for about 3,500 miles over 77 driving days, averaging 30 to 70 miles per day. The beverage company recorded payload data on 21 of those days by weighing the truck at the beginning of each day. The beginning payloads of the truck ranged from about 6,000 lbs. to 11,000 lbs. The trucks made between nine and 12 stops per day and ended each day empty.

Though the scope of this demo was limited to one vehicle’s regular duty cycle, the data illustrated through various graphs shows that weight is not necessarily the primary factor affecting a commercial EV’s range.

Payload

The first graph correlates payload with range. The ranges of the 21 days with measured payload ran from about 77 miles to 91 miles. In those days, payloads ranged from just under 6,000 lbs. to about 11,000 lbs.

The graph shows actual vehicle data on payload and range for each day payload was measured. The Y axis represents expected daily driving range, and the X axis represents payload in pounds.

The blue line shows the truck’s modeled range, which assumes no HVAC loads. The red plot point shows the average expected range over all the days from the demonstration. The black points represent the ranges for the days with measured payload, which include HVAC use. The blue point represents the average of those days.

The plot points suggest that in this demonstration, overall vehicle efficiency and range could not be estimated by looking at payload alone. “Days with lighter payload weren’t necessarily the most efficient days and heavy payload days weren’t necessarily the least efficient,” says Shawn Salisbury, data analyst and engineer at Lightning eMotors. “The performance didn’t exactly match intuitive expectations, but this can sometimes be the case with limited data.”

“While there is not a great correlation between overall efficiency, range, and payload, it is important to keep in mind that this test represents a small sample size,” says Salisbury. “If we had more data points, we would absolutely expect to see a trend that heavier payloads lead to lower range. The data from this test shows there are a lot of variables that influence efficiency on any given day.”

Those other variables are discussed in the following sections.

Ambient Temperature

It is well known that an EV operating in a cold climate will experience significantly lower range and cause a shorter battery life. This graph shows ambient temperature’s correlation to range, albeit in Sacramento’s relatively mild climate.

Salisbury notes that most of the driving days in this test took place in winter. From January to May, Sacramento’s low temperatures average 41 to 55 degrees, while the high temperatures average from 56 to 78 degrees. In Sacramento, January and February top out at 56 and 60 degrees on average, and March at 63 degrees. Those days would necessitate consistent use of heat.

“You can see (in the graph) that as the temperature gets warmer, the range increases,” Salisbury notes. “If there were a bunch of hot days in the trial, we would also expect that efficiency and range would start decreasing as you get farther right on the plot.”

Reducing HVAC load is an area of focus in engineering EVs, particularly in commercial bus applications carrying passengers. Manufacturers are assessing heated seats instead of space heaters for drivers and passengers.

Elevation Gain

The graph showing range against elevation gain is normalized into feet climbed per mile of driving. For example, a vehicle that gained 100 feet per mile in elevation and drove 50 miles would have done a total of 5,000 feet of climbing during the day.  “In general, the more climbing you do, the lower your efficiency and the lower your range,” Salisbury says.

Depending on a day’s route, this vehicle averaged anywhere from 40 to 170 feet of climbing every mile, Salisbury continues, with an average of 75 feet gained per mile.

Stops

The more often a vehicle stops — because of deliveries, or on-road stops such as stop signs or signals — the more likely the vehicle will have lower range and efficiency, as more energy is needed to get the vehicle moving again.  

An electric vehicle is, however, more efficient than an ICE vehicle when stopping and starting. While EVs have more efficient drivetrains, they also perform regenerative braking to capture the energy used to slow the vehicle down for battery use. “Every time you stop or slow down, you’re charging the batteries a bit,” Salisbury says.

In this test, for the days in which weight information was available, the number of delivery stops was between nine and 12. Salisbury says that the variations in ranges in this case are fairly minimal, because the range of stops per mile isn’t very broad — 0.5 to 1.5 stops per mile. “We have seen this trend to be more pronounced in fleets that stop more often, like five or more stops per mile,” he says.

Speed

Speed also correlates with EV efficiency. The plot points in this graph show average moving speed. The higher the speed represented by the point means that on that day the truck was able to travel on higher-speed roads, with less interruptions from stop-and-go traffic, stoplights, or intersections, or some combination of both.

“This marries with the idea that more stops mean lower efficiency. The more you are able to travel at speed rather than slowing down and speeding up, the higher your average speed and the higher your efficiency,” Salisbury says.

Driving Characteristics

How the truck is driven is a major factor affecting range. This test was conducted with different drivers of the Lightning eMotors truck, though information is not available as to which driver was behind the wheel on any given day.

Drivers’ behaviors amplify other range-inhibiting factors: Are they trained to optimize regenerative braking with heavy loads? Do they manage the temperature in the cab to minimize HVAC use? Can they moderate energy use in hilly environments?

“Driver training is crucial. It’s probably the biggest factor when it comes to efficiency and increasing range, much more than payload,” says Nick Bettis, director of marketing and sales for Lightning eMotors. “We've seen 10% to 15% increases in efficiency just based on driver training.”

Range No Issue

With varying routes, payloads, elevations, stops, and drivers in the real world of commercial driving, it’s nearly impossible to test all the factors affecting efficiency and range in a vacuum to see which one has the greatest effect.

For instance, the day with the 11,000-lbs. payload that delivered a range in the top third of the scale is an outlier — yet it may have been a mild day with fewer stops, little elevation gain, and the company’s most conscientious driver behind the wheel.

It’s clear from this analysis, at least, that payload is only one of many factors affecting EV range of a commercial vehicle. More tests of different types of commercial EVs and duty cycles are coming that will provide greater data sets to measure performance, range, and efficiency.

An ancillary note to this analysis should not be overlooked: This truck is a traditional, non-aerodynamic Class 6 low-cab forward model with a 24-foot box and auxiliary power functions such as liftgate. With a 160-kWh battery and heavy payloads, range was never an issue. The truck fit comfortably into this beverage company’s normal daily duty cycle.

As well, according to Lightning eMotors, the beverage distribution company was pleased with the truck’s performance. “They told us it was the most reliable vehicle in their fleet,” Bettis said. “They had no issues with range. At the end of the day, they could’ve used an even bigger Class 7 truck.”