Lap time assault and battery | PH Footnote
Porsche says it is working to balance electric range, performance and sustainability. It has a way to go
By John Howell / Wednesday, December 22, 2021 / Loading comments
There’s been a lot of talk about the real-world environmental benefits of buying a new battery-electric vehicle. We can argue about the variables, but the fact is you must cover a lot of miles in a large-battery EV (relative to an ICE car) before you offset the high CO2 emissions generated by its production. In a press release covering the subject, Porsche states that ‘almost half of all the CO2 emissions generated during the lifecycle of an electric vehicle are produced at the manufacturing stage, which includes the extraction and processing of raw materials.’
Second to that is the car’s usage. This depends largely on where the energy is coming from to charge it, the efficiency of the charging system and the efficiency of the motors and battery software. Recycling the car at the end of its life also adds to the CO2 debt, but that’s by far the smallest piece of the pie.
So, it follows that the biggest gains, in terms of reducing CO2, come from making the battery smaller – less CO2 from the production of the battery and also less energy used to cart all that weight around. However, that’s to be balanced with usability, which can be distilled as dynamics and range. As Porsche points out ‘the size of the battery must be right to ensure that these vehicles meet customers’ expectations and requirements.’
Most journeys are short. Typically, people drive fewer than 50 miles a day, and 80 per cent of journeys in an average week are under 280 miles. There are a growing number of small-battery EVs that cover off the typical daily trips, but Porsche customers tend to cover the longer distances, too, and expect to do so quickly. Range is obviously important, then, and it’s still the main concern for those contemplating biting the bullet and going electric. How, then, does a manufacturer like Porsche manage the compromise between becoming net carbon neutral by 2030, with supplying cars that meet its buyers’ needs? Using today’s battery tech as a constant, the first stage is finding the ideal compromise of battery size, dynamic performance and range.
To do this, Porsche has been simulating lap times around the Nordschleife using different battery configurations. As a base, it took a fictional Taycan Turbo S weighing 2,419kg with an 85.1kWh battery. In theory it would do the lap in 7:39.5 minutes, hit 0-62mph in 2.92 seconds and 0-124mph in 9.43 seconds. Reduce the battery size to 70 kWh and the weight drops down to 2,310kg. Yet the reduction in power means that the Taycan takes an extra seven tenths of a second to complete the lap, with a time of 7:40.2 minutes. 0-62mph takes 2.90 seconds (slightly quicker) and 0-124mph in 9.51 seconds (slightly slower).
Conversely, if it increased the battery size to 100kWh and added more power, the car would be slower all round. The added weight drops the lap time to 7:42.4 minutes and decreases the acceleration to 0-62mph in 3.04 seconds and 0-124mph in 9.71 seconds. Increasing the battery size to 130kWh magnifies this: 7:48.2 minutes, 3.28 seconds, and 10.48 seconds respectively.
A smaller battery, then, is the best option for reducing CO2 emissions, the medium-sized battery delivers the best driving dynamics and the larger batteries, generally, offer a greater range and therefore shorter journey times. By equipping the Taycan with 800-volt DC charging, which means it can add 60 miles of range in five minutes, tips the balance back towards the mid-size, with the optimal capacity working out to be 100kWh.
Porsche says that ‘Future battery developments will continue to enhance driving dynamics and charging times, and we can expect even greater progress in terms of reducing CO2 emissions. The second-generation electric vehicles that have not yet been launched will generate around a quarter less carbon dioxide during their lifecycle than the first-generation models.”
The problem with all this is that Tesla, still arguably Porsche’s chief rival, is already ahead of the curve on battery software and motor efficiency. For example, its forthcoming Model S Long Range has a 100kWh battery (larger than the Taycan’s 93.4kWh) yet the new Model S is said to weigh 2,069kg – 301kg less than the Taycan Turbo S. It’s also claimed to use much less energy per mile (as Teslas typically do) and therefore it has a longer range: 405 miles versus the Taycan’s 258 miles. The Taycan is by far the best electric car to drive, yet clearly it can’t claim to be the most efficient. And while Porsche’s legacy on internal combustion competes with the very best, there is scant evidence so far that it is pushing the boundaries when it comes to fully electric powertrains. Juggling its current technology to provide the best spread of performance and productivity is plainly necessary – admirable even, given the dynamic results it has achieved – but we await the kind of breakthrough it can truly boast about. Only then will longer ranges and significantly lighter cars result, to the lasting benefit of the environment and drivers both.
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