Hacker News Reader

Comment by Arnt | Hacker News Reader

Ten minutes. Is that lots of kW from the charger, or does it already pass 1MW?

Yes, just. Using a very rough 14kWh/100km from Tesla as a benchmark, 1200km would be 12x14=168kWh. That much energy in 10 minutes comes out as 1005988W.

Assume 5 miles per kWH of power, that's a little better than the average EV, but as others have noted, this battery will decrease the vehicle's overall weight and thus improve efficiency.

Then the calculation you're looking for looks something like this:

300 miles range * 1/5 kWH/mile = 60 kWH of power

We need to deliver that power in 10 mins, so:

60 kWH * 6 = 360 kW.

You need a 360 kW power feed in order to charge this battery in 10 minutes. Keep in mind the average modern household in the US has a 24kW feed, so it would take all the power available to 15 modern US households to charge this car. But it's only need for 10 minutes. Put another way, if people were continually using this commercial charging point all day long - let's say 16 hours for the day - then for the peak power consumption of 15 US households you could charge 96 cars using this fast charge.

That is an avalanche of current and you've hit on the reason the whole EV thing isn't going to work out the way some boosters think. The amount of infrastructure necessary to charge these things is ridiculous. A step-down transformer that can accomplish this feat costs a quarter million dollars, net of the pad and the wires and installation. It might be more globally efficient to re-do the entire grid as HVDC, but that might cost a few dollars as well. Far, far better systemic solutions exist, such as walking and buses and electric rail for humans, and reserving ultra-high-power EVs for cases where the payload actually needed to be moved, such as deliveries.

The thing is that if the market has already determined that Tesla's range and charge time is OK, then building a car with the same range with the shiny new tech just makes the whole vehicle lighter, by an unsubtle amount. It's hard to tell from the press release, but the implication is that they've doubled the energy density. Right now if you assume 500kg of battery and you replace that with 250kg of battery in otherwise the same 2000kg car (which is now 1750kg), that's a 12% weight saving. That's going to show up as a measurably longer range all on its own.

.. possibly a battery swap, a domestic setting getting to those MWs is out of the question. a 200 amp circuit in US at 220v is just about 44KW ..

Nobody has ever said you’d put a fast charger in your house or at work.

Getting 1MW to a commercial fast charging station is not crazy. Plenty of fast charging stations have that kind of connection. But distributed over multiple chargers of course.

What you see these days is, say, 150kW shared with t who cables. If you’re the only one charging you get 150kW. If there’s another car you get 75kW. If we ever get to 1MW I think that’ll be the model. Should still be quite beneficial since if people finish their charging faster you’ll also have more instances where you’re not sharing capacity with others.

As batteries get cheaper we’ll also see more stations with battery packs to provide peak power to those super fast charging cars.

Reply on news.ycombinator.com