Explaning ESS to a middle schooler

[Fudster]

Love it/hate it, either's fine by me.

Love it/hate it in the JL, either's fine by me.

Research shows it saves gasoline. Small amounts yes.

So...the engine stops at traffic lights and vehicle appliances run off battery power, saving gasoline, hopefully more so than any additional fuel to get the engine going again--the so called 7 second rule of ESS savings. That's the easy part.

But---that depleted battery from the ESS event has to get its energy back from somewhere, in this case an alternator, dependent on a gasoline powered engine, which presumably has to work that much harder to torque an alternator under greater load, to turn the mechanical energy of the engine into electrical energy and then into the chemical energy of the battery in need of post ESS event recharging.

I remember science lessons on how conversion of energy from one form to another loses energy from a closed system, and here where going from the chemical energy of gasoline to the mechanical energy of an engine, to the electrical engine of an alternator, to chemical energy of a battery.

So--as I see it, the way this system saves gasoline must be that given all the gasoline to get an engine up to speed, the additional or marginal extra gasoline for the running engine to torque that smart alternator beyond what it would require when the batteries are charged, is less than the gasoline savings of turning the engine off at stop lights. In fact it is so much less that we're even saving (small amounts of) gasoline despite the conversion of chemical to mechanical to electrical to chemical energy of the post ESS event battery recharging process.

How do I explain this to a middle schooler? Do I say that there are enormous economies of scale to get a car engine going such that torqueing an alternator for an already running engine is a "child's play" additional energy load in terms of the additional gasoline consumed? It's not as if other sources of energy like regenerative braking are being used in the JL (yet) to recharge an ESS battery.

Thanks.

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[Heimkehr]

@Fudster
The economist in me pivoted immediately to the idea of framing this as a modified discussion of marginal returns. Unfortunately, as I tried to [mentally] reorder it for easy digestion, the denser it got. ?

I do like your straightforward explanation, actually. Maybe explain it as is to the middle schooler (perhaps with fewer syllables where possible) and see how much of it he is capable of absorbing. Then, trim the explanation as needed based on his understanding, or not, of the process. Just a thought.

 

[mgroeger]

You are forgetting a major component and that is the AUX battery which has a very short lifespan. They can start failing as early as 2 years and if you've got the original one still at 4 you are an enigma.
So you need to factor in how much gas you are really saving for the year. It's pretty pathetic I'm guessing and then factor that against the cost of the AUX battery which resides in your Jeep to power that $hitty ESS system. This is real life, something the dip$hit ECO morons don't consider.
Everything looks wonderful and all warm fuzzies on paper but in real life there is always a trade off.

 

[Fudster]

James, we often think alike and using economics is right up my alley. Marginal returns..ok...

So the cost to the airline for the first passenger is, oh, an airplane, and staff and millions.

While the cost of the next passenger, better, on an already less than full flight (I'm not sure what the metaphor here is)---even allowing for cost accounting, is, the airline food, the greater risk/amount of the law suit if the plane crashes from one more victim, etc.

Are you saying that getting the engine going is more like the first passenger while charging the battery on a car engine already running it the cost of the passenger's meal?

What's the less already than full flight: an alternator so more capable of delivering power than the demands made of it by a battery in need of post ESS event recharging?

 

[Fudster]

You are forgetting a major component and that is the AUX battery which has a very short lifespan. They can start failing as early as 2 years and if you've got the original one still at 4 you are an enigma.
So you need to factor in how much gas you are really saving for the year. It's pretty pathetic I'm guessing and then factor that against the cost of the AUX battery which resides in your Jeep to power that $hitty ESS system. This is real life, something the dip$hit ECO morons don't consider.
Everything looks wonderful and all warm fuzzies on paper but in real life there is always a trade off.

Mike---I appreciate all of that and it's all valid. So let me rephrase the question to better get to the heart of the matter. Suppose batteries lasted forever. Suppose there little to no green footprint in their creation. Of course neither is true.

In that "candy land," "how is gasoline saved here" is really the heart of my question.

 

[Heimkehr]

@Fudster
With respect, Elliot, I'd suggest that backing into the explanation via the parallel example of airline costs -- or anything else, really -- might inadvertently introduce additional granularity that will also need excessively simplified for the target audience.

My gut instinct here is to stay strictly within the boundaries of the subject at hand, just as you mention in the preceding post: How are we saving gasoline via ESS technology?

Let me have a think and I'll be back with another post. ?

 

[Fudster]

Wait, James, I think I have a better approach. See how this flies with you.

I could make the electric from my home using my generator or I can buy it from the utility.

The utility has this freakin enormous generator that produces far more power for the amount of fuel it consumes than my less efficient generator. It does though take boat loads more energy to simply idle than my home generator.

But to run this utility generator at night (stop lights) when so few people (a moving vehicle) need its power is less optimal than my charging a battery from the utility during the day, (when the vehicle engine is on and the vehicle is mobile) and using that battery at night.

Something like that?

 

[AnnDee4444]

ESS is also about emissions.

And people on this forum could argue forever about if the emissions from gasoline are better/worse than battery production.

 

[Heimkehr]

@Fudster
Mm. I had just started to back into analyzing efficiencies via economies of scale (specifically, all of the parts that must play together to make ESS function, and the expected outcome) when your post appeared.

I like the 7 second example, not just for its simplicity, but because you can bunt to the supporting science if needed. On the point of science, your first post dives a bit into mechanical vs. chemical energy, etc. Is that something that you want to include in your explanation? Or do we want to consider just naming the components -- alternator, etc. -- and very simple explanations of their function (and not go deeper via chemical processes and so on)? I'm concerned about things getting circular too quickly.

Maybe draw a flow chart at your level of understanding, using outlines of the relevant components -- engine, battery and so on -- and simplify the flow, and the words, to make them proportionate to the middle schooler's anticipated level of understanding? Sometimes, seeing something can assist more with comprehension than just hearing it.

Still having my think.

 

[AnnDee4444]

Even if the 7 second claim isn't accurate, there's still a break-even point somewhere.

Jeeps with eTorque are using energy that would have been transmitted through the brakes as heat.

 

[John VonJeep]

If I were explaining it to a middle schooler, I would start by calling it auto start stop (ASS) and go from there.

 

[Heimkehr]

Well, I'm going to leave it with my flow chart idea for now. Domestic duties call.

 

[Chugiakguy]

Explaning ESS to a middle schooler:


ESS is stupid. ESS sucks. The end.

 

[AFD]

Jeeps with eTorque are using energy that would have been transmitted through the brakes as heat.

Doesn't the system also scavenge/regenerate energy from engine braking as well? Thought I read that somewhere, but not really sure if it occurs only when brakes are applied or perhaps when going down a hill with your foot off the gas.

Living in rural America, I highly doubt the ESS is saving me much, if any, gasoline. My commute is >90% highway, with a short trip through our small town, hitting at most maybe 5 lights and 1 stop sign. And for half of those, the ESS is usually still in a "not ready" state (still heating the cabin, inclines, other random reasons), plus the fact those lights aren't very long and I often catch them at green.

And for the times it does work when it really shouldn't, stopping the engine for a split second at a stop sign or immediately before I can get the transmission into park and turn off the engine myself can't really be good for fuel consumption or component wear either.

I actually do like the idea of ESS, but in real life it's a rather 'dumb' system that really doesn't work all that well for my own day-to-day usage.

 

[BXFXJeep]

I dunno but my 2018 JL ESS got worse mpg than my 2015 JK

I hated that ESS, that and the 8.4 were the only two things I disliked about the JL, never had any issue, they both worked as designed which was the problem.

Have a look at John's take on the ESS

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