Emission Reduction of Battery Electric Commercial Vehicles

Adaptive Fuel Cell Range Extender

5. November 2018 | Engineering Service

The transportation of goods, a key element of economic development, enables trade between producers, wholesalers, retailers and customers. However, for instance because of its emissions it causes global challenges that call for solutions. One adequate approach is the fuel cell range extender which is explained in more detail in the following.

Fig. 1: Growth of commercial vehicles and global population from 2005 to 2014

Transport services will rise at even higher rates than the growth in population, especially due to increasing e-commerce, as seen in Figure 1. The growth of commercial vehicles (CV) is also differentiated by specific markets. These trends are major obstacles to achieve the required reduction of global greenhouse gas emissions (GHG), a mandatory reduction to meet and keep the UN target limit of 2 °C in global warming. Local air pollution by transportation in densely populated urban areas is another driver towards zero emission technologies. Therefore, battery electric commercial vehicle powertrains, preferably those in combination with regenerative production of the electric energy, are strongly promoted. As stated by the United Nations, “electric drive vehicles […] need to represent 35 percent of global sales in 2030”.

In the light duty segment, e.g. postal and courier parcel distribution, the transportation of goods by battery electric vehicles (BEV) has already become reality. This trend is expected to penetrate into the larger vehicle segments, reinforced by prohibitive legislation in urban areas. Currently, the first field tests with battery electric medium and heavy duty trucks are ongoing. Of course, this transition will only be possible if cost efficient coverage of daily changing transportation tasks is maintained. This requires flexibility, which may not allow a strict limitation in range due to battery size for larger vehicles. Shift operation is especially difficult to realize with a battery electric powertrain, as known from material handling applications.

Fig. 2: Trip length distribution of 12 ton-truck fleet in Cologne-Aachen area over 10 days

Considering today’s battery electric passenger car market, the number of announced BEVs worldwide will amount to 300 vehicles in nearly all segments by 2025. While most of the currently available BEVs enable driving ranges of about 250 km, the next generation will be equipped with larger batteries with a range of more than 500 km. This range seems to be a good compromise between customer expectations, battery cost, volume and weight. For lithium-ion batteries, energy related costs of roughly 100 €/kWh and energy densities up to 300 Wh/kg are expected. The range of the vehicle is defined by the battery size, energy consumption of the propulsion system, and the accessory loads of the low-voltage electrical systems. Depending on the equipment of the car, including electronic devices for safety and comfort reasons, the power consumption can increase up to several kW peak power and an average power of about 500 W. For BEVs, auxiliaries such as heating or air-conditioning devices are powered by electric energy, which also reduce the real world driving range.

Fig. 3: Battery mass for 200 and 500 km battery electric range for different applications

The energy consumption for propulsion is strongly influenced by the weight of the vehicle. Analyzing current vehicles in the NEDC driving cycle, the power consumption is roughly 750 Wh per 100 kg weight and 100 km driving range. Using this simplified value, a 1.5 ton vehicle needs 60 kWh usable energy to achieve a NEDC range of 500 km, as seen in Figure 3. This leads to a nominal energy content of approximately 65 kWh. The weight of such a battery pack will increase the vehicle weight by roughly 200 kg. To carry this additional weight, the battery size must be increased by 20 percent again, if it cannot be compensated by weight reduction of other vehicle components. Upcoming battery electric trucks provide a range between 100 and 200 km. Exemplary data from a distribution truck fleet in the Cologne-Aachen areaover a selected timeframe of 10 days, reveals that approximately 50 percent of all day trips are within the range of up to 120 km Figure 3). It can be noted that the pure electrically driven truck, which is part of the fleet, was used only for shorter trips.
In order to substitute conventionally powered vehicles in distribution truck fleets with BEVs, electric ranges higher than 200 km are needed. As an example, a commercial vehicle with a maximum gross vehicle weight of 7.5 tons or more and a range of 500 km is considered. The battery causes additional weight or loss of payload of more than 1 ton, and additional costs of more than 30.000 €, as seen in Figure 3.

Fig. 4: ElringKlinger NM5 fuel cell stack module

In order to increase flexibility of these vehicles, fuel cell range extenders can be applied instead of increasing battery capacity. Proton-exchange membrane (PEM) fuel cells can be operated with hydrogen and the hydrogen tank can be refueled within a few minutes. During operation, only water is emitted.
The battery capacity and the fuel cell range extender power can be tailored for the main use case to reduce investment cost and total cost of ownership. The battery costs are dependent on the capacity and finally on the battery electric range. The fuel cell costs depend on the power demand, and in cases when it’s used as a range extender, costs depends on the average power demand of the vehicle.
Because of that, applications for urban use and distribution tasks are suitable fuel cell range extender applications. Use cases such as a delivery vehicle, a distribution truck or a city bus have a low average power demand compared to required peak power due to many downtimes and lower average speeds. In addition, a light duty CV for the discussed use cases has a lower maximum speed requirement.
Currently, FEV is developing a scalable fuel cell system for its customer, ElringKlinger. The fuel cell system is equipped with an ElringKlinger NM series fuel cell stack.The fuel cell stack and its system can be scaled for different CV applications between 5 to 100 kW of electric power. The fuel cell system can be adapted for different CV applications ranging from light duty commercial vehicles to trucks and busses.