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Published on September 5th, 2019 | by Guest Contributor

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Porsche Taycan — Power Hungry, Slower To Charge Than Tesla Model S (Most Of The Time)

September 5th, 2019 by  


By Simon Barke

After the unveiling of the new Porsche Taycan yesterday, analysts were quick to call the only electric competitor (the Tesla Model S) “ancient in comparison,” pointing out the “pathbreaking” 800 volt system that “slashes recharging times.” It is true that a higher system voltage can reduce charging times: you can feed more power to the battery without increasing the charge current. But just how good is Porsche’s implementation?

Efficiency

If you want to reduce charging times for electric cars, you can either increase the maximum charge power, or make the car more efficient. Ideally, you do both. Unfortunately, Volkswagen Group has some troubled history with efficient vehicles. It recently settled a lawsuit after it was uncovered that Audi, Bentley, Porsche, and Volkswagen vehicles contained illegal cheat software to exaggerate efficiency on test stands. The Audi e-tron remains one of the least efficient electric cars on the market. The new Porsche does not fare much better. If fact, it fares much worse.

Based on the European WLTP test cycle, the Taycan “Turbo S” requires 111 kWh to recharge its battery, providing a total range of 256 miles. That’s 2.3 miles per kWh, worse than e-tron’s 2.6 miles per kWh. Compare that to the Tesla Model S “Performance” with an WLTP efficiency of 3.3 miles per kWh and you see how efficient large electric sport sedans can be. The Model S is even quicker than the highest end Taycan, while the Taycan “Turbo” is only marginally faster than the Tesla Model 3 “Performance,” a car as efficient as 3.7 miles per kWh. (Fun fact: the Model 3 “Performance” causes 40% less CO2-eq emissions during electricity production than the Taycan “Turbo S.”)

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Power

Bad efficiency has an adverse effect on charge speeds. As a countermeasure, Porsche implemented an 800 volt system that can handle impressive charging powers of up to 270 kW. The stated “5 to 80% in 22.5 minutes” recharge time can only be explained if the Taycan manages to keep the 270 kW up for at least half the charging cycle. We can use this information to estimate an idealized charging profile under optimal conditions. When you compare this to Tesla’s charging profiles, the advantage of the 800 volt system becomes visible: the Model S can only maintain its maximum rating of 200 kW for the first 20–30% of the charging cycle. The same is true for the Model 3’s 250 kW charge power. (The Tesla profiles are idealized curves from real-world data that was taken during Supercharger V3 beta testing and might have improved slightly since then.)

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Keep in mind that only a handful of DC fast chargers can provide such high power. In the US, there are ten 250 kW Supercharger V3 stations available or under construction, while all other 690 stations are still limited to 150 kW but may be upgraded in the future. Although the overall charging infrastructure for the Taycan is not as good yet, there are way more stations that support the full charge power. 229 Electrify America locations that are able to provide up to 350 kW are operational today, and 71 more are planned by the end of the year.

Speed

When you know the efficiency of a car, you can translate the charge power (kWh) to charge speed (miles of range added per hour of charge). At the same time, you can scale the battery state of charge (%) to vehicle range (miles) when you know the total range. If you do that, you see that the bad efficiency and short range of the Taycan removes its charge power advantage. There is only a small area where the Taycan comes out on top. The Model S is faster during most of the charging cycle. Unsurprisingly, the Model 3 dominates the Taycan entirely.

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Time

Calculating actual charge times is tricky. Essentially, you have to integrate the inverse of the charge speed (time it takes to add range) over a certain range interval. If the battery is almost full, the time required to add more range increases significantly. For that reason, most manufacturers provide the time it takes to charge the battery to 80% or similar. However, if you want to compare different cars, we need to calculate the time it takes to add range. Let’s say you pull up to the charger with 20 miles of range left. How long does it take you to add 80, 130, 180, or 230 miles?

While the Model 3 is arguably the fastest charging electric car available to date, the Taycan “Turbo S” and the Model S “Performance” are actually head to head in terms of charge time — until the 200 mile mark. While the Model S continues to add more range at a high speed, the Taycan falls off rapidly. This is no surprise: after 230 miles of range added, the Porsche’s state of charge reaches 97% and the charge speed comes to a crawl. Tesla’s battery provides the same range at just 67% state of charge and hence can accept more energy much faster.

Notes regarding the assumptions: All figures are based on the European WLTP test cycle and idealized charge powers under optimal conditions. All charge profiles are simplified models. The Taycan’s charge speeds are estimates based on provided charge times. The Model S and Model 3 charge speeds are based on early Supercharger V3 beta tests. Tesla was unable to provide official charge profiles. Porsche did not respond to an inquiry.

Conclusion

If Volkswagen Group wants to stay competitive, it needs to start caring about efficiency. High-voltage systems and sophisticated charge profiles are workarounds that not only result in more expensive cars but also higher emissions. Is there any hope? Yes. It is believed that the upcoming VW ID.3 might actually be a very efficient car. Will the Porsche Taycan be Volkswagen’s final misstep toward a cleaner future? 
 
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