The theoretical peak output power of charging stations is difficult to maintain. The Henan Institute of Metrology Science has found that for example, with a rated power of 60 kW for a new energy vehicle, as the AC input power changes, the conversion efficiency will increase but it will always be less than the theoretical output power, and cannot reach 100%.
The output power curve is unstable, showing a slow rise followed by a rapid decline. Taking the BYD Han EV as an example, actual tests conducted by a car evaluation platform, DCD, revealed that the output power of the new energy vehicle during the charging process would slowly increase to around 110 kW. When the battery reaches 50% capacity, the output power will drop significantly to 22 kW, until the battery is fully charged. Throughout the entire charging process, the peak power is sustained for less than half of the charging time, resulting in the actual charging time of new energy vehicles being much longer than the theoretical value.
There are several reasons why the output power of charging stations cannot reach the rated power:
1. The instability of the power grid leads to unstable output power. Due to uneven grid loads and instantaneous load changes, voltage fluctuations and transient voltage fluctuations may occur during charging, which can affect the charging speed of electric vehicles and to some extent damage the battery. With the popularization of charging stations, the load on the power grid increases, leading to intensified fluctuations in grid load.
2. Battery overheating reduces transmission power. Charging stations generate a large amount of heat during the charging process, and when the battery's heat dissipation is poor, it can increase the temperature of the battery. When the battery temperature exceeds a certain threshold, it will reduce the transmission power and cause damage to the battery.
3. Energy loss occurs during the charging process of new energy vehicles. DC Charging stations can produce heat losses in cables, batteries, and other components during the charging process, which can reduce the actual output power of the charging station compared to the theoretical value.
4. Aging and damage to the EV charger stations can also reduce the output power. Aging and damage to charging stations can result in the inability to supply power to new energy vehicles at the normal power level, leading to an output power lower than the rated power.
The power grid load is difficult to meet the demand for charging station construction. The large number of charging stations puts tremendous pressure on the power grid, and the existing power grid capacity is insufficient to meet the demand for charging station construction. Taking Shanghai as an example, by the end of 2022, the number of new energy vehicles in Shanghai has reached 945,000. Assuming a power specification of 200 kW for DC fast charging, the output power when all new energy vehicles in Shanghai are charging simultaneously can reach 18.9 million kW. According to Shanghai's power grid prediction, the maximum load of the Shanghai power grid is about 35 million kW, resulting in a demand-to-actual load ratio of 5.9 times. When new energy vehicles in Shanghai are charging at the minimum power specification, it can reach 540% of the peak load of the entire Shanghai power grid. Zhang Chenyu from Guangxi University used a mathematical model to make more accurate predictions of the impact of new energy vehicle charging loads on the power grid. Taking Yiwu City as the research object, the research results showed that the power grid load is greatly influenced by the charging load, with the highest peak load generally occurring at night during winter, and during summer, the peak load is affected by weather conditions and occurs around noon. The power grid load is heavily influenced by the charging of new energy vehicles.
Under the existing power grid load, it is even more challenging to support the construction of large-scale ultra-fast charging stations. Currently, Extreme Battery has launched ultra-fast charging stations with a peak power of 800 kW, making it the charging station with the highest single-gun peak power. However, a 1250 kVA transformer can only support the charging of one 800 kW ultra-fast charging station, and a 2000 kVA transformer can only support the charging of two 800 kW ultra-fast charging stations. When ultra-fast charging stations are used on a large scale, it can lead to the collapse of the power grid system. Therefore, ultra-fast charging stations usually need to be used in conjunction with energy storage devices.
Battery swapping stations and charging stations are not mutually exclusive, and battery swapping stations are moving towards a supplementary energy supply model (battery swapping + charging). The cost of battery swapping stations and charging stations is primarily attributed to distribution and measurement equipment costs (accounting for more than 30%). The "integrated charging and swapping station" model can provide higher service capacity with the same cost and a smaller footprint. NIO's third-generation battery swapping station can be equipped with 4 to 20 super charging piles. Taking the standard charging condition with a power grid load of 630 kVA as an example, assuming the layout of 8 super charging piles in an area with 10 parking spaces, compared with a configuration of NIO's battery swapping station plus 4 super charging piles, the charging station with 8 super charging piles can fully charge 8 new energy vehicles with 80 kWh batteries, while the integrated station with battery swapping and charging can serve 12 vehicles in 5-minute cycles, and 4 super charging piles can provide battery swapping services for 4 vehicles, serving a total of 16 vehicles. In summary, integrated charging and swapping stations can provide more than 1.6 to 2 times the fully loaded service capacity compared to super charging stations under the same percentage of area occupations.
Battery swapping stations themselves are energy storage devices, and integrated charging and swapping stations have lower costs. Battery swapping stations have energy storage capabilities. They can be used to peak-shave the power grid by charging the batteries during periods of low power consumption and providing battery swapping services during periods of high power consumption, effectively balancing the power supply and reducing the pressure on the power grid. At the same time, integrated charging and swapping stations can reduce costs by sharing transformers.
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