The long-held belief that bigger is always better may not apply to the batteries powering electric trucks. While larger battery packs in electric passenger cars have been shown to increase operational costs and environmental impact, a recent analysis suggests a similar principle might hold true for heavy-duty vehicles. Fleet operators stand to gain significant savings in total cost of ownership (TCO) by opting for battery sizes tailored to typical operational needs rather than worst-case scenarios.
Addressing Range Anxiety in Electric Truck Fleets
Range anxiety remains a critical concern for owners of heavy truck fleets, where vehicle reliability is paramount for business continuity. A higher driving range translates directly into less downtime—a major impediment in the freight industry—and offers greater operational flexibility. Traditionally, diesel trucks have provided high driving ranges and rapid refueling, largely mitigating these concerns for fleet owners.
However, the transition to battery electric trucks (BETs) introduces new complexities. The substantial cost of energy storage limits the battery capacity that can be practically installed in BETs. Consequently, these vehicles often have a lower driving range than their diesel counterparts, necessitating meticulous planning of freight operations by fleet managers.
As BETs become more integrated into daily logistics, fleets are actively learning to balance battery size, range, and TCO. Advertised ranges typically reflect common usage patterns, such as urban delivery, and may not accurately represent the real-world performance for specific fleet operations. A recent study involving the European Clean Trucking Alliance indicated that actual operational ranges can sometimes exceed advertised figures due to variations in routes and payloads across different use cases.
Manufacturers offer tools designed to accurately predict a BET’s real-world range for individual fleets, a crucial step in the procurement process. Nevertheless, fleet operators often gravitate towards oversizing batteries for two primary reasons. Firstly, there’s a tendency to plan based on worst-case scenarios—the infrequent days per month when driving distances and, consequently, energy consumption significantly exceed the average. This approach prioritizes operational flexibility over cost efficiency.
Secondly, uncertainty surrounding long-term battery degradation prompts oversizing. Some operators anticipate a decline in BET range at the end of the vehicle’s life that surpasses even conservative degradation estimates. Designing for these extreme conditions means that the battery—the most expensive component in an electric truck—remains underutilized on most operating days.
The Cost of Underutilized Batteries
Research findings indicate an average battery depth of discharge of 44% in typical electric truck operations. This signifies that, on average, more than half of a battery’s capacity is unused during most operational cycles. This underutilization has a direct negative impact on the TCO, as fleets effectively pay a premium for battery capacity they do not require for the majority of their operations.
Evaluating Smaller Batteries for Daily Operations
To investigate the potential benefits of optimized battery sizing, a case study was conducted to assess whether employing a smaller, more cost-effective battery—sized for typical daily requirements—could reduce TCO without introducing significant operational disruptions, even when factoring in battery degradation over time.
The analysis utilized data from a study focusing on a 40-tonne tractor-trailer engaged in regional distribution, operating five days a week. This vehicle averaged 350 kilometers per day, with some days reaching up to 510 kilometers in worst-case scenarios. The study examined three distinct battery sizes, differing in nominal capacity: the fleet’s standard battery, and two downsized options, approximately 25% and 30% smaller.
The energy consumption of the truck was kept constant across all scenarios. It was assumed that any energy savings derived from a smaller battery pack would be offset by the ability to carry a greater payload. This approach ensures a fair comparison based on operational output rather than vehicle weight alone.
Assumptions for Feasibility Testing
Several assumptions, based on real-world freight operations studies, were made to test the feasibility of the downsized battery configurations. It was assumed that the truck would charge overnight at the depot and commence each day with a fully charged battery. Any additional energy needs not met by overnight charging were presumed to be covered by opportunity charging during the workday.
Opportunity charging, or topping up the battery at the depot, customer premises, or public charging stations, was assumed to occur at a suitable capacity of 350 kW. The primary objective was to determine if BETs with downsized batteries would require additional charging time beyond the opportunities already built into the driver’s standard working schedule.
Drivers are legally mandated to take a 45-minute break after every four hours of driving. For this study, 30 minutes of this break time were allocated for charging. Assuming an average driving speed of 60 km/h, this equates to approximately six hours of driving on an average day and nine hours on high-mileage, worst-case scenario days. This provided a baseline of 30 minutes of built-in charging time on an average day and 60 minutes on a worst-case scenario day.
Charging Time Analysis and Time Penalties
Figure 1 illustrates the total opportunity charging time required to complete daily routes for both average and worst-case scenario days, comparing it against the minimum time available during mandatory driver breaks. When charging duration exceeded the available break time, a time penalty was incurred due to longer dwell times.
With the original battery size, the truck successfully completed all delivery routes, utilizing opportunity charging within the mandated break times. The battery downsized by 25% resulted in no time penalty on average days, but incurred a 7-minute penalty on worst-case scenario days. The battery downsized by 30% led to time penalties of 1 minute on average days and 14 minutes on worst-case scenario days.
Considering that additional dwell times of less than 15 minutes can typically be accommodated without significant cost implications, minor route replanning could likely maintain operational efficiency. The trade-off for this minor adjustment in logistics is substantial TCO benefits. Battery downsizing directly reduces the vehicle’s upfront cost, leading to a TCO that is up to 9% cheaper than the baseline configuration.
Even when accounting for increased opportunity charging costs, battery downsizing still offered savings ranging from 5% to 6% compared to the default battery size. Furthermore, the reduction in upfront costs associated with smaller batteries addresses a key barrier to BET adoption for fleet owners with limited capital.
Impact of Battery Downsizing on TCO and Resale Value
Figure 2 presents the impact of battery downsizing on the total cost of ownership over a 5-year period. The analysis considers two electricity price scenarios for opportunity charging: one at the same rate as overnight depot charging (€0.274/kWh), assuming depot charging infrastructure, and a higher rate (€0.40/kWh), reflecting current public truck charging market prices.
Even with battery degradation factored in, trucks with the downsized batteries showed manageable increases in time penalties. For the original battery capacity, route coverage without time penalties remained high, decreasing from 95% to 70% after degradation. For trucks with downsized batteries, the resulting time penalties increased from a maximum of 14 minutes to 31 minutes at the most, a significant but potentially manageable increase.
Fleet Management and Battery Health
The operational implications of these time penalties largely depend on effective fleet management strategies. A recent analysis by Fraunhofer ISI highlighted that fleet-level route replanning, which integrates route and charging optimization across mixed diesel-electric fleets, can achieve higher electrification rates and greater cost reductions than simply replacing diesel trucks with BETs without operational adjustments.
The resale value of electric trucks is another critical factor. In the absence of historical data for BET resale values, financing companies often make conservative assumptions, sometimes valuing end-of-life BETs at zero residual value. This lack of clear end-of-life value can inadvertently drive fleets to oversize batteries, aiming to preserve resale value.
A more comprehensive understanding of real-world battery degradation rates is essential. Such insights would not only refine estimates of BET residual values, enabling fleet operators to size batteries based on actual operational needs rather than resale concerns, but also facilitate more optimal battery design and utilization, ultimately reducing TCO.
The Future of Electric Trucking: Smarter Sizing
The conclusion drawn from this analysis is clear: similar to passenger cars, bigger is not always the optimal choice for electric truck batteries. Fleet owners can achieve substantial TCO savings by selecting battery sizes that more accurately reflect their normal freight activities.
As fleet operators gain experience with BETs, they will develop a more nuanced understanding of real-world ranges and battery degradation patterns. This learning curve will pave the way for optimal battery sizing, tailored fleet planning, and enhanced scheduling. Furthermore, the ongoing trend towards more affordable, energy-dense batteries, coupled with advancements in high-speed charging technology, will provide BETs with increased operational flexibility without compromising high utilization rates or favorable TCO.
Ultimately, the future success of electric trucking will be spearheaded by fleets that prioritize intelligent battery sizing over simply opting for larger battery capacities.