By Ali Syed, P.Eng. PMP
With most major car manufacturers releasing electrical vehicle (EV) models, along with newcomers such as Tesla and NIO securing billions of dollars in investments, there remains no doubt that the EV revolution is upon us. The electrification of our transportation sector comes as good news to renewable energy advocates, environmentalists, and electric car enthusiasts. Implementing mass change across the automotive industry, however, does come with its own set of challenges such as sourcing raw materials for car batteries, safety of autonomous vehicles, electrical grid capacity, and EV charging infrastructure to name a few.
EVs have numerous advantages over traditional internal combustion engine (ICE) vehicles. Soon widespread adoption of personal EVs will be common and following it, a reimagining of our transportation and logistics system which includes maintenance fleet vehicles, delivery vans, and freight trucks. With range anxiety at the center of many EV discussions, the long-haul Class 8 truck is an interesting case study on infrastructure requirements for long range and high power consumption vehicles.
Until recently, the electric chargers have been categorized into three levels. Level 1 and 2 refer to AC charging while level 3 is referred to as DC Fast Charger (DCFC) based on the voltage used in each type of charging. Due to ever-increasing demand for quicker charging times and the introduction of new EV applications such as the Class 8 truck, an emerging category called extreme DC fast charging (XFC) is taking the spotlight in the public eye. A summary of output power ranges from the four categories is summarized in Table 1.
|Level 1||120V AC||≤ 4kW|
|Level 2||208V or 240V AC||≤ 22kW|
|Level 3||480V or 600V AC DCFC: 200-600V DC||≤ 50kW ≤ 350kW|
|Extreme Fast Charging (XFC)||≤ 1000 DC||≥ 400kW|
Long-haul trucks are designed for payload delivery over long distances. Quite often, the business model of these trucks are dependent on their ability to remain on the road for timely deliveries. Since fast charging times are critical to EV trucks gaining a competitive advantage over ICE trucks, it is no surprise that the development of XFC has seen a push in recent years.
Large batteries are common requirements for long range semi-trucks. Though the exact specification of these batteries varies between manufacturers, in comparison, the 600-mile range Tesla semi-truck is expected to have a battery capacity of somewhere around 1,000 kWh. Currently, the Supercharger V3 which is Tesla’s fastest charger is 250 kW. This implies that it could take up to four hours to charge the truck at maximum charger output. Keep in mind that batteries are heavy. Further increasing the size of onboard batteries to increase range will also add weight to the truck; thus less cargo can be loaded which affects the bottom line of the business.
The development and implementation of XFC does come with its own set of challenges; thermal management and grid impact being two of the biggest hurdles. As electrical power is delivered from the charger to the vehicle’s onboard battery, more energy dissipates in the form of heat due to the internal resistance of the components. In reference to a charger, larger cables can be used to mitigate the heat dissipation but at levels of 400 kW and above, these cables become too bulky and impractical. One method of addressing the cable heat is to install liquid-cooled cables that pump coolant such as Glycol to dissipate heat. This allows for smaller cables even at an XFC level. Fig. 1 shows a design of a liquid-cooling cable and connector by a company called Gilbarco.
Another consideration for thermal management can be found at the vehicle battery. Higher kilowatt power delivery requires batteries to be cooled properly to avoid battery degradation or even a fire hazard. This is a major factor in why modern car models on the road are not able to accept the full power from fast chargers for charging. Liquid cooling such as surface or tab cooling is also a viable option for managing heat on car batteries.
The logistics of a trucking business are very complex with entire mathematical theories dedicated to its optimization. In general, unlike passenger cars, semi-trucks have unique characteristics in that they typically arrive at their fueling stations in higher numbers within a smaller time-frame. To provide an XFC solution for EV trucks, added stress might be put on the electrical grid when several trucks are being charged simultaneously at high kilowatts.
One of the ways to combat this limitation is by having localized battery storage at the charging facility for peak shaving application. Load sharing and load management through the XFC energy management software may also be possible to reduce peak load on the grid, however, in many trucking applications this may not be practical since it will increase the time required to charge the truck.
Charging times and grid capability are key factors that will determine the success of the EV trucking business model. With numerous limitations surrounding XFCs such as thermal management, grid capacity, battery degradation, it is important for the EV trucking sector to find alternative methods to replenish battery capacity such as battery swap technology.
Battery swap technology is approaching speeds of under five minutes. Battery swapping will also reduce the impact of EVs on the grid as they can be charged over a longer period of time. Furthermore, through innovation, the introduction of solid-state transformers (SST) will also be able to implement reverse powerflow/bi-directional charging allowing these large truck batteries to support the grid when not utilized for the trucks.
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- Snohomish PUD studying V2G and DERMS integration with Doosan GridTech’s help
- Is the future of EV charging bidirectional?
Though many solutions are being investigated for thermal management of extreme fast charging along with innovations being made for XFC integration with the grid, a cost-effective method to address long-haul EV truck charging infrastructure remains an obstacle in the widespread adoption of this EV application. Given the complexity of the trucking industry, a more careful analysis and review of the industry charging infrastructure is needed before committing to a single solution.
About the Author:
Ali Syed is a senior electrical engineer from Hedgehog Technologies, an electrical engineering and risk management consulting firm. His experience spans designing state-of-the-art roller coasters, renewable energy systems, and industrial automation projects.