TomT said:
I think that problem with the tapering loss theory is that it does not take in to account the fact that, with a limited battery size to begin with, as the battery ages and capacity decreases, one has to use more of the available capacity to maintain the needed range (a deeper DOD) AND subject the pack to more charge cycles (a cycle being the equivalent of one charge from 0 to 100% of capacity)... This may negate any tapering of degradation...
I'm surprised to see that the model is holding up reasonably well. If the batteries are declining faster than anticipated in hot climates, we should see a proportionally faster decline in cooler locales. Personally, I'm ready to embrace a more linear decline, since that's what some of the owners who had gone through a pack replacement have seen. That said, the leveling off built into the model is based on an NREL paper, and others. I believe that Stoaty used the graph TickTock drew after a meeting with a Nissan engineer, among other things, to verify the calibration. While cycling will increase with diminishing battery capacity, cycling losses apparently still make out a minority of capacity loss. You might want to look up a
prior discussion on this.
Capacity fade models typically assume diminishing caledar losses and linear cycling losses, as evidenced by this
NREL study as well. Since the majority of the capacity fade in the LEAF will be due to calendar life degradation, we can expect this process to slow down over time. This is typically modelled with square root of time, which means that calendar life degradation seen in the second year will be about 41% of the loss seen in the first year of ownership. This diminishes to 32% in the third year, and 27% in the fourth year, and so forth.
Stoaty's model incorporates this assumption as well, and so far it has been pretty accurate, considering the field data we have collected so far. Linear cycling losses assume similar and constant charging and driving habits over time. If you have to start quick charging every day to make your commute, much like TaylorSFguy lately, or charge more often on a daily basis, then these losses could accelerate instead of remaining steady. However, since they will likely make out a smaller portion of the total degradation figure, the net effect of more agressive charging could be somewhat contained. Overall, there is a good chance that we will see the leveling off Andy mentioned in his interview.
Below is what the model from the Wiki predicts for Dallas, TX. Assumptions made: 12.5K miles annually, 4.2 m/kWh average economy, 5 days a week in the sun, 100% charging with 1 hour spent sitting at full charge.
(Many thanks to Stoaty for all the hard work that went into this).