Porsche Mission E Concept - 2015 Frankfurt Auto Show live photosEnlarge Photo
The future of electric cars for practical transportation relies to some degree on the future of DC fast charging, and how it develops over the next decade.
As in other spheres of electrifying transport, Tesla Motors has pointed the way to one vision of the future with its expanding network of Supercharger fast-charging sites.
But Tesla's network is only usable by Tesla cars.
The two standards for fast charging used by every other electric car are CHAdeMO (used by Nissan, Mitsubishi, and Kia) and the Combined Charging System, or CCS, protocol (used by all U.S. makers, except Tesla, and all German makers).
And Porsche, among others, has some definite ideas on how the CCS standard should evolve beyond its current 50-kilowatt limit.
The participants in the Society of Automotive Engineers working group for an upgraded version of CCS have already indicated their goal is to take it to 150 kw, in line with the current Supercharger at 145 kw.
Total charging time required for 250-mile (400-km) trip at various charging rates [graphic: Porsche]Enlarge Photo
Porsche also wants to boost the voltage, from its current rate of about 400 volts to 800 volts—which would effectively halve the time to recharge a battery to 80 percent of capacity, from the current 30 minute to 15 minutes.
That's fast enough to allow an owner to plug in, visit the facilities, buy water or coffee, and be done with a charge.
In its Porsche Engineering Magazine, the carmaker wrote about its proposed 800-volt system, which it has long said will be launched in tandem with the production version of its sleek Mission E electric sedan—first shown as a concept at last year's Frankfurt Motor Show.
The goal, the sports-car and luxury sedan maker suggests, should be to cut charging time to roughly the same period as refueling a gasoline vehicle—15 minutes or less—for roughly the same range.
But this will likely require liquid cooling of the charging cable, a concept Tesla has also experimented with, to prevent overheating of the charging pins.
Adding some linguistic confusion to the mix of gasoline terms adapted to electric-car usage (e.g. Supercharging), the carmaker calls this theoretical system Porsche Turbo Charging.
Total time required for 250-mile (400-km) trip on fuel or charging rates [graphic: Porsche]Enlarge Photo
Porsche repeatedly stresses the need for a charging stop on long-distance trips to mimic the experience of a fueling stop (though, presumably, without the vapors and potential spills of liquid hydrocarbons).
It suggests that payment can be made while the driver is doing other things during that 15 minutes, perhaps via mobile-phone app.
None of this will come cheap, however. "The requisite investments for charging stations are ... relatively high," it says.
Backward compatibility is a must for today's vehicles equipped with CCS, it notes.
"The interface to the vehicle is functionally and geometrically adapted to the CCS charging standard (Combined Charging System) and completely downward compatible," Porsche writes.
Further, if standards can be established for the electrical equipment to provide the necessary power, it notes, various ways to charge different kinds of vehicles could be connected to it.
Porsche Mission E concept, 2015 Frankfurt Auto ShowEnlarge Photo
"Only the interface to the vehicle has to be adapted," Porsche suggests, "which would enable such options as inductive charging and charging via a pantograph for electric buses and commercial vehicles."
At the moment, there seems to be broad agreement that liquid cooling of charging cables may be required in future DC fast-charging stations.
Backward compatibility will clearly be required for cars already on the road, and many advocates agree that the shorter the time spent fast-charging on long trips, the better.
Beyond that, automakers and equipment providers are now politicking furiously at standards meetings and beyond.
Given that Porsche's owner, the VW Group, has just committed to spend $2 billion toward a U.S. network of zero-emission vehicle charging and fueling stations, it may be wise to pay attention to Porsche's design concepts as they're fleshed out.