Thanks to all for really helpful responses, how nice to find a forum where people don’t just make sarky remarks!
Julien wrote “I remember reading the max on dual motor is about 75kW to 100kW.”
I take this to imply that if one were (improbably) to run a fully discharged vehicle downhill continuously for an hour it would completely charge the battery, ie, taking the lower efficiency figure, 75Kw/hr.
In terms of mechanics, KE=mV^2/2, so distance travelled seems irrelevant, it’s just the change in velocity? So in the example I gave it’s the energy recovered as the car comes to rest from the given speed (60 mph here) rather than the distance over which the regen operates?
However, more simply and perhaps more practically, taking SammichLover’s point about c.70% overall efficiency, using the regen would recover 70% of the distance travelled.
Or am I being over simplistic here? I think I’m understanding, just want to be clear!
If you found such a long hill, you'd eventually lose a significant amount of regen. Peaking out around ~80kW (I can't recall the exact I've seen) is pretty much Supercharging, but without the battery being preconditioned (heated) to be able to take more power. Without a hot battery, the charge rate a Model 3 can take at a Supercharger drops off quickly as the battery gets a higher state of charge. So likewise, barrelling down a steep hill for a while, you'd eventually start to get significant reductions in regen ability.
This can actually be seen in practice even with realistic hills. Coming down off a mountain highway, you'll often see some regen limitation increase. This goes away quickly with a bit of non-regen driving. They seem to be limiting how long you can pull max regen for, even more than what I outlined above.
You may be oversimplifying, but this is how we understand... basically everything in life. Little thought experiments are fun and can lead to learning things (when you see where you've oversimplified usually). I sure didn't realise that regen was variable and would decrease as it was used when I first got the car!
I don’t think that the three spur gears, differential, and four CV joints between the motor and wheels are eating anywhere close to 8% of the power, so my guess is the car might return slightly above 80% wheel to wheel, but I haven’t seen anyone test it on a modern Tesla and I’m not sure the exact numbers matter that much right now anyway.
Same. I hear people like sources, so I found this while looking (it just happens to be on the subject of EVs oddly enough):
Electric Vehicles: Prospects and Challenges | ScienceDirect
"The latter study claims that 21.5% of fuel energy in an ICEV is used in the traction of the vehicle. Fuel energy is lost through [...] mechanical losses (38%) as illustrated in Fig. 2.7.1. These mechanical losses can be further broken down into 5% for air drag and 33% to overcome friction. The figures mentioned apply to an average-sized ICE passenger vehicle (year 2000 model). The friction losses of an average-sized passenger vehicle can be further subdivided into 35% to overcome tyre's rolling friction, 35% to overcome friction of the moving parts in the engine, 15% to overcome friction in transmission, and 15% to overcome friction created during brake contact."
I'm assuming their 15% for the transmission includes all mechanical losses from engine output to the wheel hub (minus the called-out brake friction). This is 15% of the 33% total mechanical losses, so actually only 5% or so. I'd be very surprised if the limited mechanical stuff in the Model 3 adds up to 8% as well in this context, since that would imply it has
more transmission losses and a year 2000 ICE vehicle.
Looking this up is confusing, since a lot of sources are considering the losses inside the engine as well, or heat losses/inefficiencies (e.g. exhaust). This is the only one I skimmed that made it clear which part is purely the loss in mechanical transmission.
Would regen be different for RWD owners since it's a single motor?
Not really. From zero to full regen, the AWD version only uses the rear motor for regen. There are a couple exceptions to this (usually seen when navigating a parking lot, or when in reverse) but it's not meaningful in terms of power recovered.