The role of Megawatt charging in future battery electric trucking

Role of megawatt charging (MCS) in future truck electrification

The megawatt charging systems (MCS) standard will allow for charging with up to 3.75 MW in the future. In terms of charging power, it therefore extends the combined charging system (CCS) currently used primarily for fast charging of battery electric passenger cars. Today’s CCS charging stations typically provide up to 350 kW. The MCS standard is necessary, since trucks need to recharge in their mandatory break of 45 minutes after 4.5 hours of driving. Approximately 1 MW peak power will be necessary. However, it is currently uncertain to what extent charging with power in the megawatt-range will be needed. Simulation of truck driving behaviour can provide an initial indicator.

Simulation of today’s diesel truck driving as battery electric trucks

For Germany, the KiD 2010 survey on vehicle driving behaviour provides approximately 2,400 single day driving profiles from rigid and tractor-trailer trucks powered with diesel. Figure 1 shows the vehicle sample, clustered by the vehicles’ daily mileage. For all vehicles, the sample contains information on the trips of one day. A single trip consists of starting time, arrival time, travelled distance, and information on the final location (private location or public location).

Distribution of daily km travelled of the N=2,410 HDVs in the sample.

By simulating the vehicles as battery electric vehicles, necessary charging power can be obtained. It is assumed that charging events will only happen, if the state of charge of the battery will be lower than 25% before the end of the next trip. In other words, the model tries to provide a buffer of at least 25% of range. Additionally, charging events are only scheduled, if the break between two trips lasts at least 30 minutes.

To reduce peak demand, charging with the lowest possible power to fully recharge the vehicle until the end of the break is assumed. Additionally, there is a maximum average power that can’t be exceeded.

A range of approximately 500 km and a maximum average charging power of 1 MW is assumed. For sure, peak power can be higher. These values are assumed to be realistic for a broad market uptake, for example in 2030 to 2035.

Figure 2 shows exemplarily a single driving profile with 568 km daily mileage, simulated for 2035. The vehicle starts a first trip at 6:30 and reaches its first destination at 7:45 after 112 km. The intended minimum range that must be exceed with the next trip to schedule a recharging event is 390 km. 390 km are met at 14:40. However, the previous brake of 25 minutes is assumed to be too short for recharging. Therefore, the charging event takes place during the next break after 403 km at 15:00 to 15:30. To fully recharge the vehicle, a charging power of almost 800 kW on average is needed. At 18:30, the vehicle reaches its final destination and is recharged with 14 kW during the night.

Exemplary driving profile of an HDV (Rigid) with 568 km daily mileage in 2035.

Almost full fleet can soon be converted to battery electric trucks without changes

For 2030, we conservatively assumed 450 km vehicle range and an average charging power of 900 kW for tractor-trailer trucks and 800 kW for rigid trucks. Given this configuration, 93% of all vehicles can be electrified. However, since these driving profiles have typically a below-average daily mileage, only 84% of the daily mileage can be electrified. There are driving profiles with up to five daily charging events. But 58% of all driving profiles only need one charging event, 29% two charging events. They account for 70% of the daily mileage of all driving profiles.

For 2035, with 500 km vehicle range and an average charging power of 1,100 kW for tractor-trailer trucks and 1,000 kW for rigid trucks, the share of electrifiable vehicles increases to 95%, corresponding to 88% of the daily mileage. A maximum of two stops per day enables 91% of all driving profiles and 78% of the total daily mileage.

Depot slow charging enables battery electric trucking, megawatt charging is needed for long-haul operation

To better understand charging behaviour, we aggregate the simulated charging processes into three power levels: (1) charging power ≤ 44 kW, as this level could be met with AC charging, (2) charging with 45 – 350 kW on average, as this level can be covered today with the existing Combined Charging System (CCS) standard, and (3) charging with more than 350 kW, as this level will be probably served by the Megawatt Charging System (MCS) standard. It is possible that future trucks will be only equipped with MCS plugs for all levels of power. The assignment made here doesn’t contain a technical definition of the charging technology but is made for better clarity. Please note the average power within one group is smaller than the upper boarder, e.g. average power in the 45 – 350 kW group is below 350 kW, typically around 200 kW in the simulation. The first panel of Figure 3 presents the entire truck fleet that can be technically electrified (driving HDVs in dark grey and parking without charging in light grey). The second panel shows only charging vehicles. Finally, the third panel contains only vehicles with a daily mileage of at least 500 km, referred to as long-haul trucks. Obviously, most of the charging events requires only slow charging, mostly at depots: 90 % of all slow charging is at depots and 80% of 45 – 350 kW charging is at depots. High power charging with more than 350 kW power is especially relevant for long-haul trucks and only 25% of the MCS charging trucks are in depots. Typically, fast charging is performed as intermediate charging during the midday hours. One might conclude that low power depot charging is the main charging location for most future battery electric trucks and that MCS with high power is needed for long-haul operation.

Driving and charging behaviour of technically feasible BET diving profiles in 2035. Left panel: All feasible HDVs, middle panel: only charging HDVs, right panel: only charging long-haul (>500 km per day) HDVs.

Analysis presents first insights with potential for more detailed assessments

The presented analysis is based on optimistic assumptions regarding the possibility to charge almost everywhere, if the vehicle parks at least 30 minutes. In reality, the planning of charging events is likely to be more complex, especially in early years of market diffusion. The charging strategy proposed here, which foresees charging with the lowest possible charging power, minimizes the additional load on the grid. However, it is likely that charging with high power will be increasingly used, especially in public, for example to minimise the need for charging points. Nevertheless, the general statement that most charging events can be carried out at depot infrastructure with low charging power remains valid.