SeaGeo
Well-Known Member
Yes, that's unrealistic. Generally speaking EVs are quite *efficient*. For example, most EV motors are apparently around 90%+ energy efficient. Going from 90% to 95% doesn't leave a ton of room to increase efficiency. Increasing the voltage can help by reducing weight and heat loss (part of the reason Lucid went that way). Cutting weight helps in stop/go and slope speed. Hence the Lightning consumes less energy in the city rating than the Rivian, but consumes more in the highway rating than the Rivian.I have a question about battery efficiency. I currently get about 300watts/mile on a 7 year old 70d with 70k miles on it. I realize that the Rivian is inferior aerodynamically and has more weight but I would think that after 7 years of work on battery technology they would have been able to compensate for the above and match that 300 w/mi . Any thoughts on this?
I'm being a bit pedantic here, but I think it's somewhat important to note that consumption (300 wh/mi) isn't really efficiency. Two cars could have totally different energy efficiencies (say 80% vs 95%) while both consuming 300 wh/mi.
That being said, to answer your question more directly, look at the efficiency of a modern model S. Going from a 2017 S to a 2022 S you're reducing consumption fro 333 wh/mi to 285. The S is about 2,000 lbs lighter than a Lightning, has a significantly smaller cross sectional area and more aerodynamic shape, and is going to have lower rolling resistance tires given the different use cases between a car and truck.
Let's do a simple comparison. The S has a drag coefficient of about 0.21. Let's assume a highly aero truck with a bed would have a cd of about 0.3. Let's also assume that the truck has the same cross sectional area as the model S (which it obviously doesn't). At highway speed the vast majority of energy goes to pushing air out of the way. So let's figure out how efficient a current model S drive train would have to be to have the fictional truck version of the S achieve 333 wh/mi.
X wh/mi *0.3/0.21 = 333 wh/mi (target). Do some arithmetic and that lands at 212 wh/mi, which is much less than 285 wh/mi. That doesn't account for the added size, weight, or rolling resistance associated with a truck.
Now, let's take the current S efficiency and try to scale it for size and drag.I'll use the gross area of the R1T and S for simplicity in estimating the areas.
285 wh/mi *0.3/0.21 * 3.3m^2/2.6m^2 = 516 wh/mi. So right around 1.9 to 2 mi/kwh. The R1T is rated at about 480 wh/mi. So that gives about a 7% error on the estimate, well within the uncertainty the actual cross section area dimensions of each and the drag coefficient. But, it suggests that the R1T has an efficiency that's very similar to the current gen model S. And maybe a bit better.
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