Although they account for a small percentage of the total miles traveled, commercial and agricultural vehicles (CAVs) are responsible for a disproportionate amount—nearly one-fourth— of all vehicle-related greenhouse gas emissions. Electrifying these medium- to large-sized vehicles could prevent 400 million metric tons of CO2 from entering the atmosphere every year, make a significant dent in urban noise and smog, and decrease operations and maintenance costs. While some manufacturers are retrofitting traditional trucks and buses with electric motors and batteries, others are building their fleets from the ground up. Let’s take a look at some of the technology inside of these electrified big rigs and then check out a couple of models that could soon be transporting goods and people around your city.
Batteries
Today’s Li-ion batteries—the preferred “fuel tank” of electric vehicles (EVs)—store upwards of 200 watt-hours of energy per kilogram of weight. A medium-duty, low-range electric truck may have a 120 kWh battery pack, adding 600 kg to its weight, while a big rig might require 600 kWh of storage or more, packing a hefty 3,000 kg of batteries on board. According to John Goodenough, Nobel Prize winner and coinventor of the Li-ion battery, energy density could double by the middle of this decade, resulting in a decrease in vehicle weight, an increase in range, or some combination of the two.
Li-ion batteries come in a variety of “flavors,” which vary with the active chemicals in their cathodes. Two popular types are NMC (lithium nickel manganese cobalt oxide) and LFP (lithium iron phosphate), with the former providing a higher energy density and the latter offering a longer cycle life and less danger of thermal runaway. As an added bonus, LFP batteries don’t require cobalt, which tends to be mined in countries with questionable labor practices and serious human rights issues.
Charging
Most public EV charging stations with quick-charge capabilities can deliver up to 350 kW, so a truck with a 600 kWh battery pack would take almost two hours to fully recharge. It’s best not to drain a Li-ion battery to a level below 10 percent of its capacity, and once the battery reaches a 90 percent state-of-charge, it takes a long time to top off the remainder, so it’s common to do a 10-to-90 charge. For a 600 kWh battery pack, this would take about an hour and 20 minutes.
Pumping 350 kW into an EV presents its own engineering challenges related to safety and economics, and a station filled with superchargers could cause grid-level demand issues. Forward-thinking states are working with the public utilities and trucking companies to help build the infrastructure that will allow large EVs to charge as quickly as possible without disrupting commercial, industrial and residential electrical services.
Drivetrains
EV designers have a multitude of motors from which to choose, with permanent magnet (PM) synchronous motors being a popular selection due to their high torque density and smooth, quiet operation. Some electrified construction equipment, however, uses switched-reluctance motors, which are less costly due to their lack of rare earth materials. (Switched reluctance motors don’t rely on permanent magnets.) Although they don’t operate as smoothly or quietly as their PM counterparts, the trade-off is acceptable considering the environments in which they’ll operate. Even so, engineers are developing PM motors that use less rare earth material and better cooling to reduce cost, weight and heat-related magnetic degradation.
The E-axle—an electric drive that integrates the motor, transmission and control electronics into one unit—offers a simpler design, decreased weight (because all the parts share the same cooling system), and higher efficiency, so we’re seeing them appear in many new EVs of all types.
MAN Lion’s City E Bus
MAN, now a Volkswagen subsidiary, has been making medium and large vehicles for more than a century. The company recently shipped a small “demo fleet” of its new electric bus, the MAN Lion’s City E, to select customers in five European countries.
The bus’s powertrain consists of a single, 160 kW (214 hp) E-axle that delivers 2,100 nm of torque. It’s fueled by a 480 kWh Li-ion NMC battery pack, which offers a 200 km (125 mi) range. Using the 10-to-90 strategy described above, the bus’s 150 kW charger can replenish the batteries in two to three hours. The battery pack is mounted to the roof of the vehicle for modularity, scalability and safety. To reduce the impact on the electric grid and to provide a “downcycling” option for used EV batteries, the charging stations include an array of second-life batteries, taken from used Volkswagen Passat GTEs.
Volta Zero
Volta’s goal is to make the world’s most sustainable truck, and its Volta Zero, a medium-duty urban delivery truck, may very well fit the bill. Besides being a zero-emission vehicle, the Volta’s body is made from natural flax fiber and biodegradable resin, which the company says reduces manufacturing-related CO2 emissions by 75 percent. Company simulations indicate that the composite performs as well as steel in terms of crash and safety performance.
A 160 kWh LFP battery pack offers 150-200 km (95–2,125 mi) of range, and a single, rear-mounted E-axle provides a maximum speed of 90 km/hr (56 mph).
Volta also has a different way of doing business: its trucks are available under the product-as-a-service model rather than the traditional purchasing model. Customers pay a monthly fee that includes the vehicle’s use, maintenance and insurance. This model allows companies to electrify their fleets without a significant up-front cost, and to take advantage of new technology when it becomes available. And in the EV world, that’s like ... tomorrow.
Challenge Accepted
Electrifying personal transportation is a daunting challenge in and of itself, between the vehicle technology and the charging infrastructure, but trying to convert a fleet of trucks and buses raises the difficulty to a new level. The naysayers point to brownouts and blackouts, arguing that EVs will make the situation worse. In reality, engineers working for public agencies and private utilities are upgrading the grid and designing innovative solutions to build and fuel the electrified big rigs. In short, we’ve got this.