FYI: The Audi E-Tron edges out the Subaru Solterra in real-world DC fast charging tests, despite similar on-paper specs. Dive into why peak rates can be deceiving.
Decoding EV Charging: Audi E-Tron vs. Subaru Solterra
In the current EV market, the 2023 Audi E-Tron and 2024 Subaru Solterra offer competitive peak DC fast charging rates of 150 kilowatts. Despite the Subaru’s smaller battery, one might assume it would charge faster than the larger-battery Audi. Reality, however, is more complex.
Real-World Charging Performance
According to independent tests, the Audi E-Tron reaches 80% charge from zero in 30 minutes, while the Subaru Solterra takes 38 minutes to achieve the same. Not only does the E-Tron spend less time at the charger, but it also draws more energy during that period. This begs an important question: Why does the E-Tron outperform the Solterra if both boast the same peak charging rate?
The Mechanics of EV Charging
Understanding the variables behind EV charging is crucial. Although EV powertrains are simpler than their internal combustion counterparts, their engineering involves numerous factors. Battery chemistry, charging protocols, thermal management, and ambient conditions all play significant roles.
Misleading Manufacturer Claims
Often, manufacturers’ stated charging speeds are based on ideal conditions, making real-world results vary. Therefore, the listed peak rates might not always be reproducible. Like a movie theater filling up from empty, charging starts quickly with ample available space (or a low state of charge), but slows significantly as the "seats" (battery cells) get crowded.
Understanding DC Fast Charging
When charging a battery, the EVSE (Electric Vehicle Supply Equipment) supplies current to the battery, pushing electrons from the cathode to the anode. However, as the battery fills, the charging rate slows since electrons resist being crowded into an already densely-packed space.
Thermal Management: A Decisive Factor
Heat plays a pivotal role in EV charging. Any electrical current generates heat, which can accelerate battery degradation if not managed correctly. If a battery overheats, the charging current must be reduced. Extreme ambient temperatures—whether hot or cold—also affect the rate at which a battery charges, with optimal ranges ensuring better performance.
Charger Constraints and Network Dependencies
The charging rate isn’t solely dependent on the vehicle but also on the charger. Underpowered chargers and shared power between multiple charging stations can limit the speed. Additionally, mismatched voltages between EV and EVSE can further complicate efficient charging. For example, high-powered EVs like the Lucid Air may charge slower on lower voltage chargers due to the complexity and cost associated with voltage boost converters.
Charging Curves: Peaks Versus Averages
Automakers usually advertise the peak charging rate, which may only be sustainable for a brief period. Charging curves—graphs showing how the rate changes during the session—are either "steep" or "flat." A steep curve shows rapid decline after reaching the peak rate, while a flat curve maintains the peak rate longer. The Audi E-Tron showcases a flat curve, averaging 138.9 kilowatts from 10 to 90% SOC (State of Charge), whereas the Solterra significantly drops off, averaging only 71.4 kilowatts.
Implications and Real-World Performance
For marketing, both Audi and Subaru advertise a 150-kilowatt peak charge rate. However, the E-Tron sustains this high rate longer, while the Solterra quickly drops off, especially past 80% SOC. This discrepancy highlights how marketing can obscure real-world performance, making independent testing vital for consumer understanding.
Conclusion
The superior charging performance of the Audi E-Tron over the Subaru Solterra stems from its ability to sustain higher charge rates for longer durations, a reflection of its design and engineering choices. Potential buyers should look beyond peak rates and consider average sustained rates and charging curves to make informed decisions.
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William Kouch, Editor of Automotive.fyi
