BEV mass and Regeneration efficiency

[aerohead]

Originally Posted by redpoint5

It's not as simple as infrastructure not being designed with enough capacity. For one example, there's the "if you build it, they will come" problem. Make traffic flow easily between city and suburbs, and you simply extend out the suburbs, increase traffic and we're back to rush hour gridlock.

Another problem is that infrastructure built to handle peak capacity will be severely underutilized off-peak. The gridlock that occurs in cities encourages some people to modify when they choose to travel, carpool, or take mass transit to avoid congestion.

I'm not arguing for creating gridlock, only saying that it isn't a simple problem a couple geniuses can solve.

I kinda think commuting is outdated anyhow because most city jobs can accommodate distributed work rather than centralizing into a single location. Between that, and increasing automation, large gains in efficiency should be possible.

You don't. There's a moratorium on all development until the congestion issue is resolved.
Just say no.
Something Denton County, Texas has never conceived of.

[aerohead]

Originally Posted by Isaac Zachary

This is how I understand it too.

Plus more mass means more weight which means more rolling resistance.

Ideally all cars, with regen or not, would weigh as little as possible. A 1,000lb car will take about 1/6 the energy to accelerate to a particular speed than one that's 6,000lbs. If regen is 80% efficient on the 6,000lb car and the 1,000lb car has zero regen you'd still be using more net energy to accelerate and decelerate the heavier vehicle with regen than the lighter one with no regen.

When you run the numbers you'll see what the authors of the thesis were eluding to.
Then you can consider options.
There is no energy to decelerate. Only energy recovery.

[aerohead]

Originally Posted by freebeard

I re-read some of the thread.

This is masterful trolling. Possibly catagorized as 'talking past the sale'. The optimum is a balance of a number of variables. I'm not sure of the equation, but the result would be expressed in Coulumbs.

They're using differential equations to solve for about five or six unknowns simultaneously.
They've got software and parallel processor work stations.
A used scientific pocket calculator will pull back a lot of the curtain concealing the calculus.

[Isaac Zachary]

Originally Posted by aerohead

When every other consideration is made, one will discover that there is an optimum inertia for any particular BEV vehicle, from which its momentum will optimize the amount of regen that can be harvested during deceleration.
Lighter you lose.
Heavier you lose
A 'Goldilocks' mass.

This is false. There is no Goldilocks mass. I read the thesis from front to back and could not find a thing that says that. There is no optimal inertia. That is my opinion, for whatever that counts.

[aerohead]

Originally Posted by Vman455

Yes, Chalmers is a real (and well-known) university in Goteborg, Sweden. I've been there; my master's advisor was director of the GOArt organ building research department at Chalmers.

The paper argues that their models predict close to the same efficiency (as a % of total energy put in) for large vs medium vs small BEV (*on the urban cycle only*) but increased total energy consumption for heavier BEV, as one would expect. The claim that "BEV and ICE diverge" is quite correct according to this modeling, but not because BEV are more efficient as they get heavier but less, while ICE are more efficient with increased weight because the engines work at higher load and better BSFC:



And the authors note that, for the ICE model,



That is very different than claiming there is a "sweet spot at which overall optimum efficiency is achieved," as aerohead has used that to argue that increased weight of BEV isn't a detriment and may be a good thing. This paper doesn't show that. That's his own idea which he is attributing to another source to give it credibility.

Once we have a look at your results and all the others we can expand on the conversation.

[aerohead]

Originally Posted by Vman455

You have argued in the past:



You contradicted oilpan4's (correct) assertion that a lighter Model 3 would be more efficient. This paper does not support that contradiction. It clearly shows that the heavier the car is, the more energy it uses per mile regardless of the effects of regenerative braking:



You seem to be confusing efficiency of the movement of energy from battery to wheels with efficiency of energy per distance traveled. They are two different things.

1) I can't contradict an assumption of unproven 'correctness.'
2) Nowhere does the paper illustrate the 'small' Volvo V40 SUV with additional mass.
3) The only 'heavier' car would be the S80 or XC90, neither of which are germane to the V40.
4) The V40 can only be compared to itself at a different mass, which is not illustrated. This is the premise for the comment about the Tesla Model 3.
5) When you see Volvo's 'solution' to the V40 inertia issue you my want to reconsider your remarks.
6) Do the math!

[aerohead]

Originally Posted by redpoint5

I still have no idea what this thread is on about, and I don't care enough to look at the paper to try to decipher the footnote comments.

OilPan4 had made a comment about altering the mass of a Tesla Model3.
I'd read the thesis earlier and my mind went directly to something I remembered, written by the authors.

[aerohead]

Originally Posted by Isaac Zachary

Of course, and this has already been brought out, more efficiency doesn't mean better total efficiency or better miles per kWh, etc. A lighter Model 3 will get better miles per kWh even if regen efficiency drops.

A Model 3 also ususally hauls only one person and not much more, and has a limit of 5 (or is it 4?) passengers and some 900lbs total weight of cargo and passengers (although I'm sure you could add more than that). But if you could lighten it and replace that mass with even more passengers and/or cargo, then miles per kWh per passenger or lb of cargo would also increase considerably.

This whole thing reminds me of the BSFC efficiency of an ICE being at around 80% load. But if you drive around constantly at 80% load you'd actually get worse fuel mileage.

I recommend that you examine testing cycles and the other physics necessary to flesh out the details associated with the thesis.
You're describing dynamics that are not prescribed within the constraints of the mandatory test protocols.
The things you mention can all be numercalized.
All the mathematics will be required to have an actual look at what's discussed.
Without the mathematics we cannot proceed.

[aerohead]

Originally Posted by Vman455

This, exactly (emphasis added):



This is exactly what the paper shows, in these two charts which I posted previously:





Even though BTW efficiency is slightly lower for the lighter EV, its overall efficiency measured in Wh/kilometer is better than the heavier EV.

As I pointed out before, you seem to be confusing the definition of "efficiency" in the paper (percentage of stored energy that makes it to the wheels) and "efficiency" meaning the amount of energy required to travel a given distance.

1) Erase everything but the yellow diamond scatter-plot.
2) That yellow diamond scatter-plot IS the 'small' V40 SUV.
--------------------------------------------------------------------------------------
3) Show me the modified curve for the yellow diamond scatter-plot, derived from the data measured after it's mass was altered.
4) This is the only thing germane to the conversation.

[Isaac Zachary]

Originally Posted by aerohead

I recommend that you examine testing cycles and the other physics necessary to flesh out the details associated with the thesis.
You're describing dynamics that are not prescribed within the constraints of the mandatory test protocols.
The things you mention can all be numercalized.
All the mathematics will be required to have an actual look at what's discussed.
Without the mathematics we cannot proceed.

I examined the testing cycles and did the math and came up with the same conclusion that there is no "goldilocks" mass in a BEV. The evidence I see points to lighter as being more efficient overall, even though it is true that less kinetic energy can be recuperated from regen making it appear to be less efficient when it really isn't.