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A Tesla model 3 weighs 3,800 lbs. A fully loaded semi weighs 80,000 lbs. Let's just pretend that the energy requirements scale with weight - the semi needs 20x

A Tesla model 3 weighs 3,800 lbs. A fully loaded semi weighs 80,000 lbs. Let's just pretend that the energy requirements scale with weight - the semi needs 20x the battery just to go the same distance, if it needs to go ~3x as far, the semi will need ~60x the capacity of a Tesla model 3. The model 3 long range has a ~75 kwh battery pack. The Semi truck would need a battery pack that's 60*75 kwh = 4,500 kwh. The only figure I could find on a Tesla battery is that their 85 kwh pack (which had an old architecture and chemistry) weighs 1,200 lbs. A 4,500 kwh pack would weigh around 63,000 lbs. A semi truck's max legal weigh is 80,000 lbs. You'd have 17,000 lbs to make the rest of the truck and load it with cargo. Batteries have a terrible power to weight ratio. An average truck gets 6.5 mpg, a semi truck only needs about 153 gallons of diesel to go 1000 miles - that only weighs about 1,400 lbs. My point is this - rather than make the battery / cargo trade-offs, burn fossil fuels in the most efficient way possible and carry more cargo. It's a net win because we'll burn much less fuel near people (and burn less fuel than conventional trucks) and the trucks will be much faster - they'll interrupt traffic less.

Maarten88 9y ago
> Let's just pretend that the energy requirements scale with weight That would make the truck accelerate just as fast as the car at the traffic light - there is no need for that. And once it is at speed, energy requirements scales with drag - the truck may only need 2 or 3 times as much, not 20.
- alexanderstears 9y ago
  You're conflating energy and power. Maybe the truck doesn't burn energy 20x as fast going down the road, but if we compare the fuel efficiency of cars to semi trucks, it's apparent that trucks burn at least 5x as much fuel as passenger cars. But the truck does need to burn 20x the energy to go up hills so the system efficiency is going to reflect the weight difference. We can decompose the friction into two categories - air friction and mechanical friction. The mechanical friction should scale linearly with the weight, air friction is the larger term at freeway speeds so maybe trucks aren't that bad but they're not going to make an electric truck that can carry a profitable amount of cargo with the current technology. Scale the numbers accordingly, but there's a max weight of 80k lbs. Every ounce of battery cuts into the payload that pays for the truck. Battery technology just isn't there for heavy transportation - it'll get there and I hope it gets there soon but in the mean time, we should have a conversation about using fossil fuels better.
arprocter 9y ago
In that case I wonder if Tesla is going to try to stretch the definition of 'semi'

Maarten88 9y ago

> Let's just pretend that the energy requirements scale with weight That would make the truck accelerate just as fast as the car at the traffic light - there is no need for that. And once it is at speed, energy requirements scales with drag - the truck may only need 2 or 3 times as much, not 20.

alexanderstears 9y ago
You're conflating energy and power. Maybe the truck doesn't burn energy 20x as fast going down the road, but if we compare the fuel efficiency of cars to semi trucks, it's apparent that trucks burn at least 5x as much fuel as passenger cars. But the truck does need to burn 20x the energy to go up hills so the system efficiency is going to reflect the weight difference. We can decompose the friction into two categories - air friction and mechanical friction. The mechanical friction should scale linearly with the weight, air friction is the larger term at freeway speeds so maybe trucks aren't that bad but they're not going to make an electric truck that can carry a profitable amount of cargo with the current technology. Scale the numbers accordingly, but there's a max weight of 80k lbs. Every ounce of battery cuts into the payload that pays for the truck. Battery technology just isn't there for heavy transportation - it'll get there and I hope it gets there soon but in the mean time, we should have a conversation about using fossil fuels better.

arprocter 9y ago

In that case I wonder if Tesla is going to try to stretch the definition of 'semi'