Challenges in maintaining theoretical peak output power of charging stations
Charging stations struggle to maintain their theoretical peak output power. The Henan Institute of Metrology Science found that for a rated power of 60 kW electric vehicle charger, as the AC input power increases, the power conversion efficiency improves but is always less than the theoretical output, falling short of 100%.
The output power curve is unstable, exhibiting a slow rise followed by a rapid decline. Taking the BYD Han EV as an example, ESAFE's practical evaluation revealed that the output power of electric vehicles during the charging process initially increases slowly, reaching around 110 kW. However, when the battery level reaches 50%, the output power drops significantly to 22 kW until the battery is fully charged. Throughout the charging process, the peak power is maintained for less than half of the charging time, resulting in actual charging time far exceeding the theoretical value.
There are several reasons why charging stations fail to meet their rated power output:
1. Unstable power grid affects output power stability. Fluctuations in power grid voltage and momentary fluctuations caused by uneven grid load and load changes can impact the charging speed of electric vehicles and, to some extent, damage the battery. As the popularity of charging stations increases, the load on the power grid also intensifies.
2. Battery overheating reduces power transmission. DC Charging stations generate a significant amount of heat during the charging process, and when the battery's cooling is inadequate, it increases the battery's temperature. When the battery temperature exceeds a certain threshold, it reduces power transmission and can cause damage to the battery.
3. Energy loss occurs during the charging process. Charging infrastructure, such as cables and batteries, incurs heat losses during charging, which reduces the actual output power of charging stations compared to the theoretical value.
4. Aging and damage to DC charging stations can result in a decrease in output power. Aging and damage to charging stations make it difficult to provide power to electric vehicles at the normal rated power, resulting in a lower output power than the rated power.
Power grid load struggles to meet the demand for Fast charging station construction: The proliferation of charging stations puts enormous pressure on the power grid, and the existing grid capacity is insufficient to meet the demand for charging station construction. Taking a first-tier city in China as an example, as of the end of 2022, City A had a total of 945,000 electric vehicles. Assuming a charging power specification of 200 kW for a DC fast charger, when all electric vehicles in City A are charging simultaneously, the output power can reach 18,900,000 kW. According to A Power Grid's prediction, its maximum load capacity is approximately 35,000,000 kW, resulting in a demand-supply gap of 590%. Even when all electric vehicles in City A are charging with the minimum power specification, it can reach 540% of the city's maximum load capacity. Scientists have used mathematical models to make more accurate predictions on the impact of electric vehicle charging loads on the power grid. The results show that charging loads have a significant impact on the power grid, with peak loads occurring mostly at night during the winter and during the afternoon in summer, influenced by weather conditions. The power grid load is largely affected by electric vehicle charging.
Moreover, under the existing power grid load, it is even more difficult to support the construction of large-scale supercharging stations. Currently, Esafe New Energy Company (https://www.esafenewenergy.com) who supply the DC chargers has introduced ultra-fast charging stations supporting 800 kW peak power, which is currently the highest single-gun peak power of charging stations. However, a 1,250 kVA transformer can only support the charging of one 800 kW ultra-fast charger, and a 2,000 kVA transformer can support the charging of only two 800 kW ultra-fast chargers. When large-scale ultra-fast charging stations are used, the power grid system can collapse. Therefore, ultra-fast chargers 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 supplementary energy stations (battery swapping + charging). The cost of battery swapping stations and charging stations is largely driven by distribution metering equipment costs (accounting for over 30%). The "combined charging and swapping station" model can provide higher service capacity within the same area without significantly increasing costs. A powerful third-generation battery swapping station can be paired with 4-20 ultrachargers. Considering the standard charging condition of 630 kVA grid capacity, compared to the layout of 8 ultrachargers in an area with 10 parking spaces, the "combined charging and swapping station" configuration includes 4 ultrachargers. The charging station with 8 ultrachargers can fully charge 8 electric vehicles with 80% battery capacity, while the combined charging and swapping station can serve 12 vehicles with battery swapping at 5-minute intervals, including 4 ultrachargers providing supplementary energy for 4 vehicles, totaling 16 vehicles served. In summary, the combined charging and swapping station can achieve service efficiency 1.6-2 times higher than that of a supercharging station on the same area basis.
Battery swapping stations themselves act as energy storage devices and have lower costs. Battery swapping stations have energy storage capabilities, enabling them to charge the batteries during low electricity consumption periods and providing battery swapping services during peak electricity consumption times. This enables effective power balance adjustment and reduces the pressure on the power grid. Moreover, combined charging and swapping stations can lower costs by sharing transformers. During the daytime peak demand for charging and swapping, the charging station operates, utilizing the transformer's capacity. During the nighttime low demand for charging and swapping, the battery is recharged, utilizing the transformer to serve the battery swapping station. Combined charging and swapping stations leverage the characteristics of both charging stations and battery swapping stations, maximizing the use of transformers, achieving lower costs, and maintaining the power grid load without overburdening it. For more information, please visit https://www.esafenewenergy.com/blog.