Creating zero-emission heavy-duty vehicles is clearly a huge challenge, although Erik Gustafson, R&D Engineer, Chart Industries, reckons we may be further along the decarbonising trucking path than we think, as he explains some of the basics about alternative power.
In this series of articles we’ll look at two solutions being developed; battery-electric and fuel cell electric powertrains, and explain why, for long-distance, heavy-duty trucks; using liquid hydrogen storage combined with fuel-cell electric propulsion is the most viable solution.
Battery Electric Vehicles (BEVs), to give them their correct name, store electrical energy on board and are typically recharged by plugging them into the grid. An alternative is to store hydrogen on board and convert the hydrogen to electricity with an onboard fuel cell. These vehicles are referred to as fuel cell electric vehicles (FCEVs). Both are classified as EVs because they use electricity to power electric motors that drive the wheels. The principal differences between BEVs and FCEVs relate to how energy is stored on the vehicle and how they are ‘refuelled’.
Principal drawbacks with batteries are that they are heavy and bulky relative to the amount of energy they can store and require significantly longer to recharge. Simply put, today there is no practical way to implement batteries on heavy-duty vehicles such as a 40 tonne semi and have a reasonable driving range (900-1600km) with maximum payload.
Starting at the wheels, an electric motor provides the torque required to turn the wheels to propel the vehicle. On trucks, this may be in the form of an e-axle in which the electric motors are close-coupled to the wheels, or there may be one or more electric motors that power a driveshaft that powers the wheels through a differential (similar to the configuration of diesel-powered trucks today).
Upstream of the electric motor, one or more hydrogen fuel cells (FCs) generate electricity via a chemical reaction with hydrogen and air. Most fuel cells used on vehicles today are what is known as proton-exchange membrane fuel cells (PEMFCs). PEM fuel cells are ideal for vehicles because they operate at relatively low temperatures (about the same as internal combustion engines, around 82˚C and are relatively flexible in their ability to ramp up and down their power output.
Acting in parallel to the PEMFC, a small battery pack is also able to provide electricity to the electric motors. This battery pack is mainly used to store energy generated from regenerative braking and also acts as a buffer between the FC and the electric motor.
The battery pack on an FCEV is much smaller than the battery pack on a BEV as its function is not to store all of the energy needed to propel the vehicle but rather to act as a buffer. This type of system is similar to what many hybrid vehicles utilise today, power can be drawn from the engine (or FC) or the battery or both, and the engine (or FC) can drive the wheels or charge the battery pack or both.
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