On May 14, 2015, at 10:47 AM, Ben Goren via EV <ev@lists.evdl.org> wrote:

> dump pack

Thinking this through a bit more...I'm not sure that it would make sense for a 
rapid-charging station to operate without a substantial dump pack of its own.

Without one, you're left needing a grid connection able to meet your peak 
demand, which will be truly insane. Imagine a not-too-distant future where 
luxury EVs come with 100 kWh packs that people expect to charge in ten minutes; 
that's over half a megawatt. Now imagine a convoy of such traveling together on 
a road trip, all of them simultaneously pulling up to each of the 36 slots in 
the station. No way is that station going to have a 20 MW feed from the 
grid...that's about 5% - 20% of the output of a utility-scale generating unit. 
And even the utilities themselves would have problems running such a facility 
because of the sharply peaking nature of the load.

But if, on average over the course of a day including times when all slots are 
empty, the station only "sees" one or two stalls in use at a time...well, a 
megawatt utility connection is still pretty freakin' huge -- 1 kV @ 1 kA, or 
however you want to balance the two -- but much more manageable. You'd keep a 
constant rate (or, perhaps, varying per utility feedback but averaged to a 
constant) of charge going into your massive dump pack, and each of the slots 
would feed from the dump pack, rapidly depleting it for just a short period of 
time as the grid constantly trickle-fills it back up again.

Again...the scale of such operations pretty much demands that they be insanely 
expensive, especially compared against a 110V / 15A overnight charge that'll 
more than satisfy almost all of almost everybody's needs once vehicles can 
reliably get over 200 miles on a full charge.

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