Hacker News Reader

Comment by reaperducer | Hacker News Reader

88,000 people in perhaps 50,000 vehicles all taking the ONE road out of town.

That's an interesting point.

We see this a couple of times a year in the United States — tens, or even hundreds of thousands of people evacuating because of an approaching hurricane.

It takes hours and hours and hours to go not very far. And when you finally get someplace with an open hotel room, it's hundreds of miles away.

Although I believe they are close, I'm not sure EVs are ready for that challenge yet. Especially since a gas station half-way to safety can fill up hundreds of cars faster than a dozen EVs can charge.

Can more chargers solve this problem? Better chargers? Both? Something else?

View on HN

> Especially since a gas station half-way to safety can fill up hundreds of cars faster than a dozen EVs can charge.

Logistics. A petrol station can fill up any single isolated car or truck really fast, but when the local supply is gone, it can only be returned via a delivery truck (unless I'm very wrong and they have pipes direct to refineries?)

An electric charger can recharge one car battery much slower than a tank can be refilled, but the grid can be approximated as "not running out" over that kind of timescale.

I'm not sure which would be better for mass evacuations in practice, especially given traffic jams are where EVs excel.

Even cars are barely up to the challenge in that case.

At a minimum we need some sort of fast charger that can add 50+ miles in 5 minutes. Granted, in a gas car that's a full tank usually, but let's be reasonable about what we can expect in the near-ish future.

Having wireless tech that can charge that fast would be even better. Maybe get on a little conveyer belt similar to an automated carwash and by the time you exit, you have 50 more miles than before. Hell, imagine these things running parallel to a road like a pit lane on a racetrack. Move on the track for 5 minutes, then they turn around and grab cars going the opposite direction.

Seems pretty inefficient and probably a logistical nightmare, but it would be cool to see it work!

We already have those fast chargers. The average EV gets 3-4 miles/kwh. 50 miles would be about 15 kwh. To deliver 15kwh in 5 minutes, you'd need 180kw charging. The fastest widely available chargers currently go up to 350kw. Kia EV6/Hyundai Ioniq 5 charge from 10-80% (>200 miles) in 18 minutes (due to battery limitations).

We can already do more than 50 miles of range in 5 minutes. For example a Tesla Model Y is rated at about 0.234 kWh/mile, round up to 0.25 kWh/mile. To get 50 miles of range you need 12.5 kWh, in order to get that in 5 minutes you need a charging speed of 150 kW. Tesla V2 superchargers already do 150 kW and V3 does 250 kW, which would only take 3 minutes to get 50 miles of range. Of course the actual charging curve depends on your battery state of charge but 50 miles in 5 minutes is very achievable in most cases, at least with Tesla.

Now doing this in a portable way is the difficult part. There are a few trucks now that can do 7-10 kW output to charge cars, but that's only about 30-40 miles of range per hour, which is still quite slow. But it might be enough to top you up for 15-20 mins to get you 10-15 miles down the road to a charger. I imagine this will improve though quite a bit as more EVs are adopted. I think if we can get to 50 kW chargers from service vehicles that's good enough. On a 50 kW charger 15 minutes of charging will give you 50 miles of range on a Tesla, and on less efficient cars it will still give you at 30+ miles.

You can do a lot better than that; just electrify the roads so that cars can recharge while travelling at highway speeds.

https://www.theguardian.com/environment/2018/apr/12/worlds-f...

There's basically three options: overhead lines, which are cheap but kind of ugly and don't really work for passenger cars (they'd need a really tall pantograph to reach as high as a truck), rails embedded in the road surface which can be used by cars and trucks but are more expensive than overhead lines, and wireless charging which is much more expensive than rails and the amount of power you can reasonably transfer is pretty limited.

I'm in favor of the rail approach, like they're testing in Sweden. If some billionaire with money burning a hole in your pocket is reading this, might I suggest buying a stretch of land parallel to a busy highway and constructing a parallel road with rail-style charging, and establish an in-motion charging standard. Let people charge for free and see what comes of it.

In the long run I hope all the major highways get electrified this way. It's disappointing that Congress isn't already working on this.

Something else to consider is that EVs can remain idle in traffic without consuming much battery. They're not constantly consuming fuel like most ICE vehicles.

But if you're fleeing a hurricane, chances are you have the air conditioner on. It's generally hot and humid. You. Any have the windows open because of the rain, but you need the AC to keep the windshield clear. How does that affect battery use in an EV?

Tesla has "Camp Mode" which can regulate the temperature for nearly two days on a full charge.

I don't have a Tesla, but maybe someone here does and can chime in.

You can idle a ICE car for maybe 16 hours easily with a half-tank, although this varies a lot [1]. With rationing your fuel, running for 10-30 minutes for every hour, you can maintain survivable temperature for at least double that (32 hours on half tank) to perhaps 96 hours, or 4 days. Double that for a full tank of gas.

If you want EVs to take over, get feature parity with the current technology.

[1] https://www.autotrader.ca/editorial/20190201/how-long-can-yo...

Reply on news.ycombinator.com