Powerwall 2 Degredation vs Charge capacity

[arf88]

Hi, I'm about to purchase two powerwall 2 for my home, but before I sign the contract I'm trying to do my due diligence to get info on the cell chemistry. My goal with these two batteries is to use them 100% only for power outages, with Edison threatening to shut down power in high wind scenarios which is frequent but they have not shut power yet in the area i would like to have backup power since the generac generator did not work out due to city setback rules for permits. I already have a solar system, oversized so I'm never going to use the battery to offset costs. It will strictly be used for backup power only.

I would like information on charging and storing powerwall 2 battery charged at 100% with minimal cycles and degradation over time. There is a pretty good chart i pulled from a youtube video showing Telsa model 3 battery info but this depicts thousands of cycles. I'm familiar with Li chemistry to know charging at 100% is not ideal but the rate of degradation is very much dependent on the cell chemistry and software managing the battery. Not knowing much about the powerwall 2 I'm hoping someone here might have some with a similar chart. The dilemma is at 80% charge I'm giving up 20% capacity for those hot summer days when the AC is on so I would like to know what the actual rate is and make a determination on what to leave the battery charge level do daily until it is needed.

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[Pipe-Light Inc]

Wondering myself this type of info. They are certainly heavy 250+ and I would suspect you are mounting in basement, Garage... I envy you having a solar system. It is a full on battle here in Neoconservative land Florida where my wife's family love them some church, Some B-B-Q and all the fixens of being a slow down heavy weight human that can eat all the food and electricity FPL want to throw their way...

Anyway, cant wait to see the replies. Still holding off on both this and SOLAR until I have saved the CASH outside of investment... But also looking for the next downturn and lower prices that will eventually come along. FPL here now has fields of Solar and do everything they can to stop the consumer from doing the same.

[Mike90250]

First you need to find out if the powerwall BMS already manages the capacity for 20-80%. You don't want to duplicate that.
I know their sales droids push the full rated battery capacity 0-100% but I'm sure the BMS has some restrictions.

PS you may need/want a little eu1000 generator to keep going overnight and not bleed the batteries totally dry.

[arf88]

Wondering myself this type of info. They are certainly heavy 250+ and I would suspect you are mounting in basement, Garage... I envy you having a solar system. It is a full on battle here in Neoconservative land Florida where my wife's family love them some church, Some B-B-Q and all the fixens of being a slow down heavy weight human that can eat all the food and electricity FPL want to throw their way...

Anyway, cant wait to see the replies. Still holding off on both this and SOLAR until I have saved the CASH outside of investment... But also looking for the next downturn and lower prices that will eventually come along. FPL here now has fields of Solar and do everything they can to stop the consumer from doing the same.

I couldn't be happier with my system, but I knew what I wanted and didn't let any of the sales sell me something. Best thing when you are ready pick the equipment you want and pit their bids against each other for the best deal.

[arf88]

First you need to find out if the powerwall BMS already manages the capacity for 20-80%. You don't want to duplicate that.
I know their sales droids push the full rated battery capacity 0-100% but I'm sure the BMS has some restrictions.

PS you may need/want a little eu1000 generator to keep going overnight and not bleed the batteries totally dry.

This is the part that I'm unsure about. In a tesla related forum I asked the same question and a user with the system said you can't set the charge rate. It is always 100% but when the systems detects a storm using their stormtracker system it allows you to charge more so that tells me there is no way the 100% correlates to a true 100% battery capacity charge. With the Warranty they offer i doubt Tesla would let their batteries charge to 100%, that is the only way they can guarantee the 10 year/70% cap. Li technology has not changed that much over the years and they aren't using any unicorn cell chemistry as far as i know so the same Li rules apply. I just want to know what kind of capacity 100% is and degradation which I don't think any one has the info on.

I don't know if the BMS can be changed at all by the user, if the feedback from that user is correct you have no control at all.

I contacted Tesla, the first level tech support said great question but couldn't provide an answer, so he is going to reach out to manufacturing. I think expecting them to provide some feedback is wishful thinking. I have until next Wed to sign the contract otherwise the SGIP is not guaranteed by solar company and I'm not willing to take that chance.

[Ampster]

I think the chemistry has been tweaked a little and has a slightly different electrolyte. If you are using it just for backup I would not worry about it. Yes Tesla is conservative at 100% is not 100% of State of Charge. There are complete threads going on for pages about various Powerwall user experiences on TMC. I don't recall anyone on this forum remarking that they have a Powerwall. I had one on order and decided to roll my own using a Outback Skybox. My brother just installed one on a vacation home on Mauai. His experience is too recent to give you any help.
If you have Net Metering you may want to consider Time Based controls to improve your rate of return. Are you in California?

[arf88]

Thanks for the feedback, yes im in california, I have no need to offset them, i don't want to cycle them to make them last longer. My PV system is oversized so there is no benefit for me to stress out the battery since I'm already over producing monthly. I agree i don't think 100% is truly 100% capacity at all. Shame they don't provide more info from the MFG.