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Powerwalls stop charging once reserve ratio hit

rubch

Member
Jun 25, 2021
6
2
Orinda, CA
Hi everyone, I just got Tesla solar & Powerwalls installed and had a question on charging behavior. I'm using time-based control with PG&E's EV2-A time schedule, and using Cost Savings with an 80% reserve ratio. I was surprised to see that the Powerwalls stopped charging once they reached 80% capacity during off-peak hours, and the solar then starts sending power to the home and grid. I would've thought that the Powerwalls would charge fully during off-peak hours so long as excess solar was available. Am I missing something here? I can't find another thread that discusses this situation. Thank you for any insight!
 

holeydonut

Supporting Member
Supporting Member
Jun 27, 2020
2,104
1,486
East Bay NorCal
Hi everyone, I just got Tesla solar & Powerwalls installed and had a question on charging behavior. I'm using time-based control with PG&E's EV2-A time schedule, and using Cost Savings with an 80% reserve ratio. I was surprised to see that the Powerwalls stopped charging once they reached 80% capacity during off-peak hours, and the solar then starts sending power to the home and grid. I would've thought that the Powerwalls would charge fully during off-peak hours so long as excess solar was available. Am I missing something here? I can't find another thread that discusses this situation. Thank you for any insight!


Can you take a screenshot of your App configuration for time based control on Weekdays? It'll help us see what you've set up...

But I agree with you it's odd the PW's aren't charging up first before solar energy is exported to the Grid.
 

rubch

Member
Jun 25, 2021
6
2
Orinda, CA
Yes, of course! I think the below screenshots cover the relevant settings, but let me know if I'm missing something. Thanks!

IMG-5349.PNG
IMG-5350.PNG
IMG-5351.PNG
 

holeydonut

Supporting Member
Supporting Member
Jun 27, 2020
2,104
1,486
East Bay NorCal
Hmmm, try getting rid of the shoulder times. I am in PG&E land with EV2A, and I just set my peak to be 3pm to midnight. Basically the big blue bar and big orange bars are the only ones I use. The shoulder thing was acting funny for me.

Also, if your system was just set up there's a chance it's just learning and testing settings. I set my reserve all the way down to 15% because I want to try and get through 3pm to midnight where my home loads are 100% supported by Powerwall or solar (excess going to the grid during that time).
 

rubch

Member
Jun 25, 2021
6
2
Orinda, CA
Thanks for sharing your experiences with this. I'll set the reserve lower and see how the system works over the next few days. And if that doesn't work, I'll give the shoulder removal a try as well. Thanks again.
 

miimura

Well-Known Member
Aug 21, 2013
6,478
6,229
Los Altos, CA
The question I have is why the SOC was below the Reserve in the first place. The batteries should only discharge to the Reserve, then go into Standby. If this was the first day running Time Based Control, just leave it alone for a few days and see what it does.
 
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astrorob

stealth performance M3
Aug 27, 2014
483
111
oakland, ca
the shoulders are working for me on EV2A (the powerwall kicks in at 3pm and discharges till 12am). i don't know if the PW software actually tracks the cost of the banked electricity or whether it just looks at off-peak vs. everything else when deciding to charge or discharge. but i agree that there seems to be a "learning period" after commissioning and it is possible it's just acting funny because of that.

the only 'weirdness' i've seen with mine (and i asked about it here for clarification) is that if the PW thinks it can make it to the end of the high-priced time given the reserve you've set, it might not charge to 100%. however when the reserve is 80% and it stops charging at 80%, it seems like it's not thinking about that particular strategy but something else is going on.
 

getakey

Active Member
Jan 28, 2020
1,398
447
95762
Not in Cost Savings mode. If it thinks it won't need the power the next, or later that day, mine will stop charging prior to 100% and get what it can with the power.
You're right, but I've only seen that on Fridays when it knows it can get to 100% on Off Peak the next day versus Shoulder on Friday
 

aesculus

Still Trying to Figure This All Out
May 31, 2015
4,516
2,570
Northern California
You're right, but I've only seen that on Fridays when it knows it can get to 100% on Off Peak the next day versus Shoulder on Friday
I had only seen it on Fridays too but I got more solar recently (well really back in December but we won't repeat the details on why its more now) and it can happen other days too. It's hard to put my finger on it but I have seen some crazy stuff going on that looks logical once you step back. Like today after peak it went back to charging the powerwalls even though it was clear it would not need them the next day (Sunday). And I have seen some strange behavior mid week too.

So I think Tesla has been playing with Cost Savings mode a bit more recently and/or me having more solar available has made it different. I used to just about get to the end of peak when the battery reached my reserve. But now I often find even at 40% I don't get near there some days.

I will say this: Trying to figure all of this out and end the year at net 0 kWh or slightly negative is a challenge. The weather can make such a difference.
 

getakey

Active Member
Jan 28, 2020
1,398
447
95762
I had only seen it on Fridays too but I got more solar recently (well really back in December but we won't repeat the details on why its more now) and it can happen other days too. It's hard to put my finger on it but I have seen some crazy stuff going on that looks logical once you step back. Like today after peak it went back to charging the powerwalls even though it was clear it would not need them the next day (Sunday). And I have seen some strange behavior mid week too.

So I think Tesla has been playing with Cost Savings mode a bit more recently and/or me having more solar available has made it different. I used to just about get to the end of peak when the battery reached my reserve. But now I often find even at 40% I don't get near there some days.

I will say this: Trying to figure all of this out and end the year at net 0 kWh or slightly negative is a challenge. The weather can make such a difference.
I didn't like the behavior so I eliminated all Shoulder. The PWs put me into negative NEM so I don't need optimized cost savings. After my first year with PWs and negative NEM, my first priority is backup now especially with theses hot temps. I put my reserve at 50% to 60% depending on the forecast.
 

h2ofun

Active Member
Aug 11, 2020
2,919
555
auburn, ca
I didn't like the behavior so I eliminated all Shoulder. The PWs put me into negative NEM so I don't need optimized cost savings. After my first year with PWs and negative NEM, my first priority is backup now especially with theses hot temps. I put my reserve at 50% to 60% depending on the forecast.
I still have mine at 10%. The 3 batteries make it though the night with AC, even though 19% this morning. But once the sun comes out, I am find.
 

holeydonut

Supporting Member
Supporting Member
Jun 27, 2020
2,104
1,486
East Bay NorCal
Nope, I set peak from 3pm to 1am. When I get up at 4am, 100% still coming from batteries. These are my 2 GW's from yesterday. Can see I am basically totally off grid this time of the year.

View attachment 678493

View attachment 678494


Are you in cost savings mode?

Due to conversion losses, you lose a bit when your batteries are exporting energy during off-peak. This is because the PG&E meter has no conversion losses while the PV you banked into your batteries is slightly diminished if it actually goes into the batteries and comes back to you. So you'd prefer to use your batteries as little as possible and have as much solar generation overflow into the grid.

Of course the shoulder and peak rates are way worse than the conversion loss under PG&E EV2A, so you would gladly have your batteries exporting during shoulder and peak time.
 

rubch

Member
Jun 25, 2021
6
2
Orinda, CA
Thanks for all the input on this. Apparently it was either a glitch or just the system learning the ropes after just getting turned on as it's working as expected now.

The SOC was below the reserve as the batteries were quite low when the system turned on, so it wasn't that the system let the batteries go below the reserve.
 

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