The reality of tesla?

[bolosky]

Since Tesla has to run cells in series and parallel higher energy density cells could mean fewer cells over all for the same voltage and ah capacity.
For example right now their cells are 3.7 volts at 2.4ah, there are already cells available at 3.7 volts and over 3ah. If at some point they hit 3.7 volts at 4.8ah per cell you can use half as many cells for the same performance and range, but actually better of both since you'll be hauling less weight.
After a certain amount more range becomes pointless. It all depends on driving habits but I'd much rather have a lighter vehicle with 300 miles range than the same weight and 500 miles range. I'd never use that much range, and by hauling around less weight I'd need fewer batteries per mile.

I think you're confusing energy and power density. Going from 2.4ah to 4.8ah doesn't (necessarily) mean you get twice the current from the cells, it probably means that you get the same current for twice as long.

With current technology, you can get high power/low energy cells or vice versa, but not both. My point is that the Roadster needs the number of cells that it has to generate the power to get the acceleration (and presumably to absorb the power from the regen breaking). Unless the power density of the high energy cells, or the energy density of the high power cells gets better, you're stuck with the current cell count or lower performance (or, I suppose lower range if you switch to high power density cells).

When the Tesla folks were in Seattle last fall, someone asked them about building a Roadster with a half-sized battery pack (and so lower weight & higher acceleration) for track use. They said that it wouldn't work because they need all the cells they have for power, so I'm guessing that there's not all that much wiggle room.

 

[JRP3]

It's very possible that ah capacity can increase AND power output can increase. Case in point, the newest prismatic cells from Sky Energy at 180ah are the same size as their older 160ah cells, and the C rate has increased from 3C/10C to 4C/12C. Even if the C rate didn't increase 1C from the newer cell is higher than 1C from the older cell.
I'm surprised Tesla has stated they need the full pack for performance, does the vehicle's performance significantly decrease with a half depleted pack?

 

[JRP3]

I think you're confusing energy and power density. Going from 2.4ah to 4.8ah doesn't (necessarily) mean you get twice the current from the cells, it probably means that you get the same current for twice as long.

My understanding of cell rating is the ah rating is the 1C rate, so 2.4 to 4.8 at the same C rating should mean twice the current in the same amount of time.