4 ms·

Right, BUT - everyone tends to make those long trips at the same time. Thanksgiving, Mother's Day, Spring Break, Easter, Passover.

mikeash 11y ago
Most of those trips aren't that long. The average Thanksgiving trip is a bit over 200 miles, for example: http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/america_on_the_go/us_holiday_travel/html/entire.html http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/pub... Maybe 40% of gas cars will need to stop for fuel during a trip of that length, assuming a range of 500 miles and refueling when near empty. EVs should be able to make it directly, since they'll start at 100%. You're absolutely right that the network needs to be sized for peak demand much higher than average demand, but even then I think it's less than what you'd need for the same number of gas cars.
- ams6110 11y ago
  Why do you assume you're starting at 100%? That doesn't seem like a given to me. You go to work on Wednesday, maybe run a couple of errands, and then leave on your Thanksgiving drive. It's nightime in November so you need the heat and the headlights. There are no superchargers within 50 miles of your planned route. Now what?
  - mikeash 11y ago
    Yes, in that scenario you'd have to stop. But then gas station usage goes up too. There's some crossover point where the EVs need more, but I don't think this gets you there. By the way, don't mention headlights. Their power consumption is absolutely negligible. Heat, for sure, but not lights.
    - Grishnakh 11y ago
      Headlight consumption is "absolutely negligible"? I've measured D2S headlight consumption at about 3A, or 6A for a pair; roughly 50W total, and it's constant. While I'm sure that's a lot less than you're using for propulsion or heat, that still doesn't seem quite "negligible". Of course, the on-board computer in the Tesla, plus its giant LCD screen and backlight, probably use at least that much continuously.
      - mikeash 11y ago
        Yes, negligible. Cruising on the highway uses about 20kW. 50W total is 0.25% of that. If you drive for three hours, the total energy consumption of the headlights during that time would be enough to move your car another half mile. Minor stuff like the precise air pressure in your tires, minor variations in wind, or different road surfaces will have a much bigger effect. Put it another way: if you somehow convinced the car to leave the headlights on permanently, and you weren't plugged in, the headlights by themselves would take nearly two months to drain a 60kWh traction battery from 100%.
        Grishnakh 11y ago
        It's pretty amazing how much energy capacity they're able to put in that battery pack. 60kWh could run a clothesdryer for roughly 20 hours straight. Out of curiosity, what's the "sweet spot" for efficiency for a Tesla? I imagine modern highway speeds aren't the best because of wind resistance. I wonder what the energy consumption is at, say, 45mph. Would you be able to extend the range significantly that way?
        mikeash 11y ago
        It is pretty amazing. Note that Tesla doesn't even sell the 60 anymore, their current low end is 70kWh, and the high end is 90kWh. (A 100kWh will probably be introduced pretty soon, based on leaked info from the firmware.) The Model 3 will probably have a smaller battery, as it won't need as much, and that will save cost. 60 seems like a decent bet, although it might be as small as 50 or 55. On the other hand, it's an amazingly small amount of energy. A 90kWh battery holds the equivalent energy of 2.7 gallons of gasoline. It's just that the electric drivetrain is 90+% efficient at turning that into motion. The optimal speed for maximum range is about 25MPH. The slower you go, the less energy you waste fighting air resistance. I assume that below that speed, the energy that goes into maintaining the various systems start to cancel out the gains from going slower. The current record for a Model S is 452.8 miles, which took almost 20 hours. Not exactly practical. Slowing down more reasonable amounts definitely helps. According to Tesla's range calculator, with a 70F outside temperature and no climate control, a 90D can expect to go 275 miles at 70MPH on level ground. Drop to 65MPH and you can get 302 miles. At 60MPH, the range is 332 miles. This is always good to keep in mind on longer trips. You can watch your projected state of charge on arrival, and if it starts to drop below where you're comfortable, just slow down a little bit and that should solve the problem. Obviously, it's best if you don't have to do this, but it's a good plan B or plan C to keep in your pocket.
Grishnakh 11y ago
You could always just rent a regular gas car for those long trips. Or just take an airplane or Amtrak or a coach.

mikeash 11y ago

Most of those trips aren't that long. The average Thanksgiving trip is a bit over 200 miles, for example: http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/america_on_the_go/us_holiday_travel/html/entire.html http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/pub... Maybe 40% of gas cars will need to stop for fuel during a trip of that length, assuming a range of 500 miles and refueling when near empty. EVs should be able to make it directly, since they'll start at 100%. You're absolutely right that the network needs to be sized for peak demand much higher than average demand, but even then I think it's less than what you'd need for the same number of gas cars.

ams6110 11y ago
Why do you assume you're starting at 100%? That doesn't seem like a given to me. You go to work on Wednesday, maybe run a couple of errands, and then leave on your Thanksgiving drive. It's nightime in November so you need the heat and the headlights. There are no superchargers within 50 miles of your planned route. Now what?
- mikeash 11y ago
  Yes, in that scenario you'd have to stop. But then gas station usage goes up too. There's some crossover point where the EVs need more, but I don't think this gets you there. By the way, don't mention headlights. Their power consumption is absolutely negligible. Heat, for sure, but not lights.
  - Grishnakh 11y ago
    Headlight consumption is "absolutely negligible"? I've measured D2S headlight consumption at about 3A, or 6A for a pair; roughly 50W total, and it's constant. While I'm sure that's a lot less than you're using for propulsion or heat, that still doesn't seem quite "negligible". Of course, the on-board computer in the Tesla, plus its giant LCD screen and backlight, probably use at least that much continuously.
    - mikeash 11y ago
      Yes, negligible. Cruising on the highway uses about 20kW. 50W total is 0.25% of that. If you drive for three hours, the total energy consumption of the headlights during that time would be enough to move your car another half mile. Minor stuff like the precise air pressure in your tires, minor variations in wind, or different road surfaces will have a much bigger effect. Put it another way: if you somehow convinced the car to leave the headlights on permanently, and you weren't plugged in, the headlights by themselves would take nearly two months to drain a 60kWh traction battery from 100%.
      - Grishnakh 11y ago
        It's pretty amazing how much energy capacity they're able to put in that battery pack. 60kWh could run a clothesdryer for roughly 20 hours straight. Out of curiosity, what's the "sweet spot" for efficiency for a Tesla? I imagine modern highway speeds aren't the best because of wind resistance. I wonder what the energy consumption is at, say, 45mph. Would you be able to extend the range significantly that way?
        mikeash 11y ago
        It is pretty amazing. Note that Tesla doesn't even sell the 60 anymore, their current low end is 70kWh, and the high end is 90kWh. (A 100kWh will probably be introduced pretty soon, based on leaked info from the firmware.) The Model 3 will probably have a smaller battery, as it won't need as much, and that will save cost. 60 seems like a decent bet, although it might be as small as 50 or 55. On the other hand, it's an amazingly small amount of energy. A 90kWh battery holds the equivalent energy of 2.7 gallons of gasoline. It's just that the electric drivetrain is 90+% efficient at turning that into motion. The optimal speed for maximum range is about 25MPH. The slower you go, the less energy you waste fighting air resistance. I assume that below that speed, the energy that goes into maintaining the various systems start to cancel out the gains from going slower. The current record for a Model S is 452.8 miles, which took almost 20 hours. Not exactly practical. Slowing down more reasonable amounts definitely helps. According to Tesla's range calculator, with a 70F outside temperature and no climate control, a 90D can expect to go 275 miles at 70MPH on level ground. Drop to 65MPH and you can get 302 miles. At 60MPH, the range is 332 miles. This is always good to keep in mind on longer trips. You can watch your projected state of charge on arrival, and if it starts to drop below where you're comfortable, just slow down a little bit and that should solve the problem. Obviously, it's best if you don't have to do this, but it's a good plan B or plan C to keep in your pocket.

Grishnakh 11y ago

You could always just rent a regular gas car for those long trips. Or just take an airplane or Amtrak or a coach.