After reviewing the entire picture of fast charging, I found that due to the different usage scenarios of electric vehicles , it is difficult to reach a consensus when discussing the same topic from different perspectives.
The topics discussed can be divided into the following three categories:
Category 1: Public transport vehicles (buses)
Public transport companies, public vehicles, and DC charging infrastructure. In this field, public transport companies dominate vehicle characteristics, determining the required range and charging speed of their products based on the fixed routes and coverage of buses.
In this field, local authorities have direct decision-making power regarding the characteristics and procurement of vehicles based on the actual conditions of their operating routes. Therefore, while the basic characteristics of components are similar, the vehicles and facilities exhibit a high degree of decentralization. Unlike private users who rely on fast charging based on battery capacity, the public transportation industry lacks fixed customers and faces significant uncertainty. Consequently, it's difficult to categorize these vehicles as large-scale bulk purchases; they resemble customized production, resulting in a wide variety of market segments for buses. Local bus companies determine the charging time for each bus based on the characteristics of their routes to meet daily needs. The lost charging time is factored into the cost of additional vehicles the bus company needs to purchase, which is why electric buses require fast charging.
Note: According to the guest, the current solution for electric buses is to use dual guns to charge them at approximately 400-450 amps (700 volts for the bus, with a total power estimated at over 300 kW). Therefore, the design of the individual battery cells, bus cables, and connectors for electric buses requires very high standards.
Figure 1. Publicly operated vehicles
Category 2: Privately owned and heavily used vehicles (logistics and taxis)
The system comprises operating companies (including businesses and individuals operating ride-hailing services), production tools (vehicles), and fast-charging facilities. Taxi companies purchase electric vehicles and charging facilities, then operate them through electric taxi drivers. The charging speed is determined by the ratio of time spent by the driver charging the vehicle to operating time. Strictly speaking, because drivers of these vehicles receive subsidies for charging, they are entirely focused on charging as quickly as possible before starting operations. All lost operating time (charging) is essentially lost potential income for the driver.
Figure 2 Fast charging requirements for taxis
Since both of these types of vehicles use electric vehicles as means of production, they have strict requirements for charging speed, so there is no upper limit. In pursuit of speed, vehicle costs (with limited increases), daily maintenance requirements (replacing battery modules), and the power requirements of centralized charging stations are no longer issues. The main bottleneck here lies in the trade-off between the lifespan of individual battery cells (fast charging often results in capacity loss, requiring a balance between speed and loss).
At the same time, these two types of charging facilities can be said to be pre-arranged and dedicated to specific vehicles, so there is no need to consider availability issues throughout the entire cycle; they are matched one-to-one. Therefore, in a sense, this is a planned usage scenario.
Category 3: Electric vehicles used privately.
Car owners, electric vehicles, and DC charging infrastructure. This is the category we will focus on, because it is the existence of private vehicles that allows electric vehicles to gain a foothold and maintain long-term, continuous demand, thus supporting the continued development of this category. Let's look at the characteristics of this type of vehicle:
1. Differences in battery capacity and driving range lead to two different charging and usage patterns for private electric vehicle owners. Based on statistics, most owners drive less than 50 kilometers daily, and their slow charging habits are as follows:
Owners of long-range electric vehicles can choose to charge 2-3 times a week, have confidence in their driving range, and be able to cope with possible emergencies.
Owners of low-range electric vehicles, due to the limited range of their vehicles, often choose to charge daily after the vehicle's range deteriorates rapidly towards the end.
Figure 3 Charging habits at different mileages
2. For private car owners, fast charging is generally mainly used for emergency charging.
On the one hand, the current charging speed is limited, which means that car owners will not leave their effective control range. On the other hand, the inherent investment in DC charging stations is relatively high, and the calculated charging service fee is also high. When electricity costs plus charging service fees are calculated, the actual cost per 100 kilometers is comparable to fuel costs.
Table 1. Comparison of Electricity Costs for Electric Vehicles
3. Private vehicles have a long usage period. Based on an 8-year warranty, the possible changes in charging conditions for a pure electric private car are as follows:
A car's charging situation can be quite complex. Initially, there might not be a DC fast charging network nearby, so the owner might not use DC charging at all. However, as the fast charging network expands, the owner might develop their own habits and start using it frequently.
The differences between cars are significant, and the charging options for different cars also vary greatly.
4. The entire system (charging system and battery system) has high cost requirements.
Faster charging speeds place higher demands on battery and charging systems, and the charging speed (power) also puts higher demands on batteries and related components. Simply put, DC fast charging systems have electrical and safety requirements for the external power distribution box, and higher-performance DC fast charging systems also impose new standards on the thermal management capabilities of the battery system.
Considerations regarding individual cell lifespan: This is explained quite clearly in the open course and several articles by Professor Liu Guanwei. When selecting a battery, the frequency of using DC fast charging is limited; however, an experiment can be conducted to verify the battery's adaptability to fast charging.
Figure 4 Overview of the DC fast charging system
summary:
Because electric vehicles are used in different scenarios, it is difficult to reach a consensus when discussing the same topic from different perspectives.
From a current commercial perspective, batteries can only reach the expected balance point with very heavy use. Therefore, fast charging is a hard requirement in this regard, characterized by high speed and high frequency, resulting in more fast charging than slow charging. From the perspective of promotion and usage, fast charging becomes an occasional demand, with high charging speed required but infrequent use.
From the perspective of charging networks, it has become an industry practice for fast charging networks to revolve around dedicated, fixed usage frequencies, with long-term operational revenue offsetting investment. However, considering the commercialization of fast charging networks for ordinary consumers, fast charging is still more of a loss-making business, facing the problem of low frequency of use for long-term revenue. Car owners often charge unplannedly or out of necessity, requiring more breakthroughs in operation.
For more information, please follow the Automotive Manufacturing Channel.
