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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 cu

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
  >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. The only problem with that kind of comparison is that the energy in combustible liquids isn't actually usable for propulsion like that. There's no way (that we know of yet) to turn 90+% of the energy in gasoline into propulsion; most of it is just going to be wasted as heat due to the Carnot Cycle. Of course, if your goal is to simply produce heat (like for heating a building), fossil fuels are pretty effective at that. Gasoline-powered fuel cells might do somewhat better than regular ICEs, but still nowhere near 90+%. In a nutshell, electricity is by far the most efficient form of energy transfer we've found so far. Everything else ends up wasting lots of energy to heat any time it's converted from one form to another, but a good electric motor can convert electric energy to mechanical energy with 98% efficiency (and vice-versa, with generators).
  - mikeash 11y ago
    I wouldn't say it's a problem with that comparison so much as the point of it: it illustrates the relative efficiency of the two. It also illustrates some side issues, like why an EV will suffer significant range loss when you need a lot of heat, while a normal car doesn't care.

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
>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. The only problem with that kind of comparison is that the energy in combustible liquids isn't actually usable for propulsion like that. There's no way (that we know of yet) to turn 90+% of the energy in gasoline into propulsion; most of it is just going to be wasted as heat due to the Carnot Cycle. Of course, if your goal is to simply produce heat (like for heating a building), fossil fuels are pretty effective at that. Gasoline-powered fuel cells might do somewhat better than regular ICEs, but still nowhere near 90+%. In a nutshell, electricity is by far the most efficient form of energy transfer we've found so far. Everything else ends up wasting lots of energy to heat any time it's converted from one form to another, but a good electric motor can convert electric energy to mechanical energy with 98% efficiency (and vice-versa, with generators).
- mikeash 11y ago
  I wouldn't say it's a problem with that comparison so much as the point of it: it illustrates the relative efficiency of the two. It also illustrates some side issues, like why an EV will suffer significant range loss when you need a lot of heat, while a normal car doesn't care.