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Is it bad to leave Powerwall 2 at 100% SoC?
- Thread starter Chippylad
- Start date
I believe that the 100% charge as shown in the app is not actually 100%. People have noticed that one of the things that stormwatch mode does is charge the batteries “beyond 100%”. You can’t see the percentage go up to 105% or 110%, but if you watch it charge while it’s in storm watch mode the powerwalls will hit 100% and then keep charging for a while. And likewise, when the powerwalls get used after that happens the house will draw power from the powerwalls for a while before the app shows them dropping from 100% to 99%.
So the short version is, even though the app shows them at 100%, the actual SOC is something less than that to help protect the batteries.
So the short version is, even though the app shows them at 100%, the actual SOC is something less than that to help protect the batteries.
I’ve heard that 100% is really 90% for PWs but since it doesn’t show the ‘over 100’ it is hard to quantify. It definitely isn’t 100%. Mine live at 99% and I know it’s not really 99% as that’s awful for lithium batteries.
Short answer: don’t worry about it.
Short answer: don’t worry about it.
Don't know if this is related to the charging over 100% but the datasheet shows two "capacities" for powerwall 2: total energy 14 kWh and usable energy 13.5 kWh. So a SOC of 100% might really be something like 96.4%
There is also a difference between SOC shown by the app and the one reported by the gateway on the internal webpage - see thread here
There is also a difference between SOC shown by the app and the one reported by the gateway on the internal webpage - see thread here
We had two storm watches in the past month, and I looked at the data, it did not charge to 100% or beyond. It only charged to 99%.
That is what I saw in the single storm watch event - 99.08% is the highest number we hit.
Do you record any data about how much power is being sent to the powerwall? It would be interesting to see if it was at 99%, then stormwatch hit and it then absorbed another, say 1.5kWh.
At 17:49 (all times UTC, not that it much matters) on that day, my PWs reported a charge of 96.9990%. That is when storm watch kicked in, and raised the battery level to 99.0771% at 17:55. It slowly declines from there (to 97.9718% by 12:00 the next day.) I do not know exactly when storm watch disabled, but it appears there is only that one charging event associated with it (and I can see the difference from the normal recharge that occurs in backup-only mode because it actually pulled from grid and not just available solar.)
During that time, 620 Wh were added to the PWs. As we have two of them (new, so hopefully little degradation,) and depending on exactly how the power conversion losses are accounted for, this matches very well with seeing the battery level rise by about 2.1 percentage points.
As a side-note, the charging rate over the 5 minutes is 6.7 kW, which seems to match well with what others have seen as the maximum for storm watch of about 3.3 kW per powerwall. It looks like Tesla reports data in increments of 10 Wh, so some minutes imply 7.2 kW, but I think that is just a rounding issue and not indicative of the power fluctuating.
I leave my pair set at 100% but keep in mind they are still discharging 2-3% over a given 48 hour period and then recharging from solar when they hit about 96.5%..... so they actually are cycling. From what I have read this is actually the best scenario to preserve performance and increase lifespan. I've only used my Powerwalls in the event of grid outages.....and in my longest outage of about 5 days my PW's never dropped below 50% because of good solar production.
I did a test to see how much energy I can draw from 2 Powerwalls when it reaches 5% (0% in app). I was able to draw 22.2 kWh total before it stopped (it was in Self-Powered with 0% reserve in app). Assuming one-way inverter loss is 5%, this means that 22.2 kWh is 23.37 kWh in battery, and it represents 95% capacity, so 100% would be 24.6 kWh. Since the 2 Powerwalls have capacity of 14 kWh each, or 28 kWh combined, it means that 100% in api means 87.9% of actual battery level.
I have documented my test in this post:
Energy in 2 powerwall drained from 100% down to 5%
I have documented my test in this post:
Energy in 2 powerwall drained from 100% down to 5%
100% SoC is mainly a concern for those who leave the powerwall in Backup-Only. This mode is used when utility doesn't have peak and off-peak rates, and therefore there is no incentive to use the battery on a daily basis, and 100% of the energy is preserved for power outages. So there is no ROI, and for that reason, users would tend to minimize the cost and buy fewer batteries. In my case, I bought only 2 batteries, and they are already degraded by 15% after 2 years. 15% of 2 batteries could keep the lights on between 4-8 hours. That's a big deal.I have my 3 powerwalls go on after solar has stopped daily. Every morning the batteries start charging to 100%. And the cycle starts daily. Hardly use any pge now. All solar and back up.
But in your case, and since you are saving money and the powerwalls are paying for themselves, you should keep using them as much as you can, and down to the reserve level you are comfortable with.
