I would love to see half size or smaller units so that you could get an extry level 240V system without having to buy two massive and expense units. The second unit just seems like a waste compared to 120V percent usage vs 250V. Maybe a full size unit that can dynamically switch between various mixed usages of 120V & 240V decides.
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Discussion: Powerwall 3 [Speculation / Discussion etc]
- Thread starter n.one.one
- Start date
CrazyRabbit
Active Member
Powerwall 2 is 240/120. I think you misunderstood something.
I wish there was a way to limit the max state of charge you charge the power wall to. For example I would like to be able to limit the max charging state to 85% with the idea that I would extend the cycle life. I actually recently put this request into the support tech time.
this thread has me confused now..... What is the best routine for extending the performance and lifespan of the PW's? I keep mine set at 100% and only draw them down during grid outages. Is it healthier for them to be cycled more regularly? Or should I lower the reserve to something less than 100% (e.g. 80%?) so they get a little daily exercise?
thanks!
thanks!
ucmndd
Well-Known Member
This goal is unfortunately at odds with a potential switch to LFP cells, which are significantly less energy dense.
CrazyRabbit
Active Member
I don’t think there is any truth to dc bus. That went bye bye with powerwall 1.
LFE cells are a done deal, just will they be cylindrical or prismatic. I hope for cylindrical, which is safer and lends it self to a better thermal solution.
I would like to see a way for the tesla inverter to cold start the gateway and powerwall, perhaps with a second disconnect switch to isolate generation from loads to allow the powerwalls to charge a little. But the inverter could easily power the 12 bus to start up the system.
Would like to see a 400 amp gateway.
LFE cells are a done deal, just will they be cylindrical or prismatic. I hope for cylindrical, which is safer and lends it self to a better thermal solution.
I would like to see a way for the tesla inverter to cold start the gateway and powerwall, perhaps with a second disconnect switch to isolate generation from loads to allow the powerwalls to charge a little. But the inverter could easily power the 12 bus to start up the system.
Would like to see a 400 amp gateway.
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This is really all about competition. I doubt that will come from specialized ESS products, but maybe from EV's equipped with V2H capabilities. Tesla seems to not be interested in this capability on their vehicles, so maybe the other automakers can be more aggressive and differentiate that way. Certainly the case for battery storage ONLY for load shifting and self consumption don't make sense now, though maybe with income based pricing it will be better.
Jeremy3292
Active Member
From a strictly technical perspective, nickel based lithium ion cells prefer to be around 40-60% state of charge (SoC) with a shallow(er) depth of discharge (DoD). The higher SoC you have the more degradation you will experience. This is not linear so somewhere north of 80-85% the degradation begins to increase more heavily, which is a much more practical SoC for daily use. It is the same as you would charge your Tesla car with nickel based chemistries (LFP chemistry is different). Hence why Tesla recommends keeping your car between 20-80% SoC as much as you can.
Of course it all depends on how much you care and how much you want to be a nerd about it.
Calendar Aging of Lithium-Ion Batteries
Degradation of Commercial Lithium-Ion Cells as a Function of Chemistry and Cycling Conditions
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They dont, though (Tesla). Thats almost entirely on forums. Tesla says to charge it anywhere between the sliders for daily use (which is 50% to 90%), there is no recommendation at all from Tesla on "20% to 80%" thats all forum thread talk (some of it very technical, but its till not something that Tesla itself recommends).
The reason I am making this distinction is people do this exact thing all the time, and its not correct. If you want to say "forums and data show in general XXXX" then yeah. If you want to say "Tesla recommends..." then no, thats not correct.
From my limited reading on Teslas website to use things like 240V HVAC systems they state you need (recommend) two powerwalls.
What am I missing?
Or was it that with 240V a single power wall maxes out at 30A which limits how much else you can backup at the same time given the power draw for many HVAC.
So maybe for 240V two PW are strongly recommend and not necessary required?
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Jeremy3292
Active Member
You're right Tesla doesn't verbatim say "keep between 20-80%" but that is essentially what the owners manual says in practice.
The Model 3 owners manual states the following:
It does say 90% instead of 80% but the 20-80% window is often quoted for ease of remembering (avoid the top and bottom 20% windows). It also notes regular charging (e.g. low DoD) is a best practice as well.
We are going to have to agree to disagree that anything you posted there says anything at all, or even infers anything at all, about 80% to 20%. Those numbers are not mentioned anywhere in the manual, nor are they mentioned in any other official tesla information, nor even tweets by official tesla engineering people or the ceo.
ucmndd
Well-Known Member
Yes, this. It has nothing to do with voltage, rather max power output. A single powerwall 2 can supply 5kw continuously, and ~7kw peak, thus the 30 amp max breaker spec for a single unit (30 amps at 240v is 7.2kw).
So what’s Tesla’s rationale for suggesting two powerwalls when you want to backup HVAC and / or electric ranges? It just take up all the power while nothing let for frigs, lights, tvs, etc?
ucmndd
Well-Known Member
Again, it’s max power output. Many HVAC units require startup current far greater than 5-7kw. Induction ranges typically require a 40-50 amp breaker so they can easily draw more power than a single powerwall can provide.
Jeremy3292
Active Member
80% to 30% is better
Which is from 2014 and a different battery makeup than any model 3 or Y, but I stand corrected on "never said it".
Jeremy3292
Active Member
CrazyRabbit
Active Member
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