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what I learned today - or why my powerwall doesn't fully charge from solar every day

I've had a "behavior" with my Powerwalls recently - and today after a very helpful chat session with an excellent Tesla support representative I now fully understand what was/is going on and how to work around it.

Problem/Behavior Statement: My system was not fully charging my Powerwalls on a daily basis - it was cutting "off" my battery charging and leaving the Powerwall system @ 70-85% capacity even though I had plenty of solar production to "fill up" the batteries. This was frustrating me - because we have a lot of outages in our area and I want my batteries to be top capacity so that I have plenty of power for our outages.

My Settings: Time based Controls - 50% backup capacity - w/PG&E EV-A rate schedule "entered" in the system with full off-peak, mid-peak, peak TOU rate windows entered for both week days - and weekends and the two "seasons".

what I found out…

with "Time Based controls" the powerwalls develop a history/prediction of how much power is going to be used during "peak" - during the off-peak/mid-peak rate period the Powerwall software will endeavor to optimize to only charge the Powerwall system enough above my 50% setting to make it through the peak period and "land" back at 50% capacity as it "exits" the peak power TOU rate time window. The "excess" solar produced during the mid-peak TOU-rate-time-window will be pushed to grid for NEM credits rather than used to top-off the batteries.

solution to this "problem/behavior" - in working with the Tesla phone support representative - we decide to "lie" to the Powerwalls about the TOU rate period and I removed the "mid-peak" TOU-time-windows and now my TOU schedule only contains "off-peak" and "peak" TOU-rate-time windows. In implementing this "work around" I have now seen an immediate change in behavior and the Powerwall system now uses as much "off-peak/mid-peak" solar production as it can to fill the batteries (my goal) - rather than "stopping" at the predicted capacity required to provide sufficient power for the predicted "peak" consumption time-window on the same day.

now that I understand the problem I can see why/how the Powerwall does this - but this behavior is not my preference as I have the powerwalls for backup given numerous outages in our area - but I also like to use the Powerwalls to "defend" my home and NEM bill against PG&E "peak" rate periods with my own solar and battery power.

I want to use my power to defend again "peak" rates, but not be forced to then live overnight at what ever "min" % I've selected - charge to 100% every day - and use what you need to for peak - but most of the time I want as much power as I can have for overnight - not 50%+peak-usage charging target - and always 50% overnight…

the solution of excluding "mid-peak" from the rate-schedule is an acceptable work around in my opinion - but less than ideal.

Problem: why isn't my powerwall filling up everyday when there is plenty of off-peak/mid-peak solar to provide sufficent power to top-off the batteries?
Reason: the powerall is trying to only harvest "enough" solar power from mid-peak to "meet" predicted consumption for peak on that date/day-of-week- and sell the "excess" back to grid at mid-peak rates
Solution: adjust your powerwall rate schedule mid-peak TOU time windows to reflect your personal preference about when you wouldn't mind selling mid-peak solar power to grid rather than using that power to charge your batteries.
  • I understand what the Powerwall is doing now.
  • I can see that someone might want it to behave that way and it's quite clever
  • But it's not my personal perference for how it should behave - so for now I've removed my mid-peak TOU-time-windows
NOTE: in reviewing my history you can see how well the predictions do in terms of history - ie.e if you look back in time at your energy graphs - you can review on what days your battery "cut off" before the end of the peak-rate period and you used solar/grid power to "finish" the peak rate period - in reviewing my data - the system's predicxtions are accurate most of the time and it actually does a really really excellent job of predicting peak power usage and what amoutn of power it needs to dump into the batteries to cover your peak usage, there by maximizing the available power to sell during mid-peak from "excess" solar…

so kudos to Tesla for coming up with this really clever behavior - but alas it's not my perference as to how it shoudl behave.

mostly I don't like "exiting" the peak rate period (9 pm most days) at 50% battery - I'd rather "exit" the peak rate period time-window with as much power for overnight for an outage - rather than the target "minimum backup" amount

also now that I understand this - I'm comfortable adjusting the minimum backup lower - 25% - because I know on most nights 25-30% will cover my peak usage window - but if I let Tesal manage it - it would only ever charge my batteries enough to cover peak time window and land back at 25% - which isn't very outage friendly…

I share this in the spirit of what I learned today- apologies if everyone else already understood this - but you learn something new every day - and this was my item for today.
 
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the "problem" with the work around is that the "solar value" estimates will now be off - since it will accrue "off-peak" per-kWh "value" for the solar power rather than the "mid-peak" value for the solar power…grrr

I believe tesla needs to add a preference to "time-based-controls" to "fully charge" the battery as an option - or only charge to "meet-estimate-peak demand" in settings/preferences…

another advantage of the "workaround" is that while I saw that the Powerwall estimate was often scary accurate and it did successfully predict my peak-time-window usage - and land the battery at exactly 50% - sometimes it was off (as estimate/predications based on past behavior can be) and it would occassionally "run" out of power "early" in the peak window and be forced to let PG&E provide power at the tail end of the period - by fully charging the battery and having a lower backup minimum - there is much less chance of running out of battery power during the peak rate period.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
16,678
21,961
Riverside Co. CA
I've had a "behavior" with my Powerwalls recently - and today after a very helpful chat session with an excellent Tesla support representative I now fully understand what was/is going on and how to work around it.

Problem/Behavior Statement: My system was not fully charging my Powerwalls on a daily basis - it was cutting "off" my battery charging and leaving the Powerwall system @ 70-85% capacity even though I had plenty of solar production to "fill up" the batteries. This was frustrating me - because we have a lot of outages in our area and I want my batteries to be top capacity so that I have plenty of power for our outages.

My Settings: Time based Controls - 50% backup capacity - w/PG&E EV-A rate schedule "entered" in the system with full off-peak, mid-peak, peak TOU rate windows entered for both week days - and weekends and the two "seasons".

what I found out…

with "Time Based controls" the powerwalls develop a history/prediction of how much power is going to be used during "peak" - during the off-peak/mid-peak rate period the Powerwall software will endeavor to optimize to only charge the Powerwall system enough above my 50% setting to make it through the peak period and "land" back at 50% capacity as it "exits" the peak power TOU rate time window. The "excess" solar produced during the mid-peak TOU-rate-time-window will be pushed to grid for NEM credits rather than used to top-off the batteries.

solution to this "problem/behavior" - in working with the Tesla phone support representative - we decide to "lie" to the Powerwalls about the TOU rate period and I removed the "mid-peak" TOU-time-windows and now my TOU schedule only contains "off-peak" and "peak" TOU-rate-time windows. In implementing this "work around" I have now seen an immediate change in behavior and the Powerwall system now uses as much "off-peak/mid-peak" solar production as it can to fill the batteries (my goal) - rather than "stopping" at the predicted capacity required to provide sufficient power for the predicted "peak" consumption time-window on the same day.

now that I understand the problem I can see why/how the Powerwall does this - but this behavior is not my preference as I have the powerwalls for backup given numerous outages in our area - but I also like to use the Powerwalls to "defend" my home and NEM bill against PG&E "peak" rate periods with my own solar and battery power.

I want to use my power to defend again "peak" rates, but not be forced to then live overnight at what ever "min" % I've selected - charge to 100% every day - and use what you need to for peak - but most of the time I want as much power as I can have for overnight - not 50%+peak-usage charging target - and always 50% overnight…

the solution of excluding "mid-peak" from the rate-schedule is an acceptable work around in my opinion - but less than ideal.

Problem: why isn't my powerwall filling up everyday when there is plenty of off-peak/mid-peak solar to provide sufficent power to top-off the batteries?
Reason: the powerall is trying to only harvest "enough" solar power from mid-peak to "meet" predicted consumption for peak on that date/day-of-week- and sell the "excess" back to grid at mid-peak rates
Solution: adjust your powerwall rate schedule mid-peak TOU time windows to reflect your personal preference about when you wouldn't mind selling mid-peak solar power to grid rather than using that power to charge your batteries.
  • I understand what the Powerwall is doing now.
  • I can see that someone might want it to behave that way and it's quite clever
  • But it's not my personal perference for how it should behave - so for now I've removed my mid-peak TOU-time-windows
NOTE: in reviewing my history you can see how well the predictions do in terms of history - ie.e if you look back in time at your energy graphs - you can review on what days your battery "cut off" before the end of the peak-rate period and you used solar/grid power to "finish" the peak rate period - in reviewing my data - the system's predicxtions are accurate most of the time and it actually does a really really excellent job of predicting peak power usage and what amoutn of power it needs to dump into the batteries to cover your peak usage, there by maximizing the available power to sell during mid-peak from "excess" solar…

so kudos to Tesla for coming up with this really clever behavior - but alas it's not my perference as to how it shoudl behave.

mostly I don't like "exiting" the peak rate period (9 pm most days) at 50% battery - I'd rather "exit" the peak rate period time-window with as much power for overnight for an outage - rather than the target "minimum backup" amount

also now that I understand this - I'm comfortable adjusting the minimum backup lower - 25% - because I know on most nights 25-30% will cover my peak usage window - but if I let Tesal manage it - it would only ever charge my batteries enough to cover peak time window and land back at 25% - which isn't very outage friendly…

I share this in the spirit of what I learned today- apologies if everyone else already understood this - but you learn something new every day - and this was my item for today.

This is a very good write up of this behavior. This behavior is sort of why the stickied thread on multiple peak times etc exists, and why people were clamoring for more control prior to tesla allowing multiple peaks etc.


Good explanation, OP.
 
This is a very good write up of this behavior. This behavior is sort of why the stickied thread on multiple peak times etc exists, and why people were clamoring for more control prior to tesla allowing multiple peaks etc.


Good explanation, OP.
my apologies for the "duplicate" post - feel free to remove it - or copy/paste my text if you feel it's worth while into an existing thread.

I agree we need more control - but a simple Time-based controls - with an optional check box - √ - always fully charge batteries - would do the trick. I'd even accept the check box being 'off' by default which would mirror the current behavior.

I feel we lost something in the transition from the old settings of time of use with two sub-options "balanced" and something else…
 
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jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
16,678
21,961
Riverside Co. CA
my apologies for the "duplicate" post - feel free to remove it - or copy/paste my text if you feel it's worth while into an existing thread.

I agree we need more control - but a simple Time-based controls - with an optional check box - √ - always fully charge batteries - would do the trick. I'd even accept the check box being 'off' by default which would mirror the current behavior.

I feel we lost something in the transition from the old settings of time of use with two sub-options "balanced" and something else…

I can merge it into that one if you want me to, but I thought this was a good explanation of the specific thing you were talking about (good enough to stand alone even though there is a thread on the general topic).
 
I can merge it into that one if you want me to, but I thought this was a good explanation of the specific thing you were talking about (good enough to stand alone even though there is a thread on the general topic).
great - I don't mind a stand alone thread on this particular topic and specific issue - I've reviewed the other threads and while informative they are a little more wide ranging…
 

ucmndd

Well-Known Member
Mar 10, 2016
9,448
18,351
California
I struggled with this a lot on EV-A as well. Time Based Control is all about maximizing savings and the behavior it exhibits absolutely does that. That’s my primary objective so I’ve come to just live with it. I also like keeping the powerwalls with as much reserve as possible so I adjust my reserve up/down through the season as necessary to maximize cost savings while also keeping the PWs as charged as possible. If your powerwall has “learned” you need ~30% to power your house during peak, change your reserve to like 60-65% instead of 50%.
 
Last edited:
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aesculus

Still Trying to Figure This All Out
May 31, 2015
4,967
2,892
Northern California
When you all say you are on EVA is that EVA the original, or EVA2? I am on EVA the original and have two PWs and the only time my PWs don't fill to 100% is on Fridays, and sometimes on Thursdays. I move my reserve from 30% to 50% depending on how risky I want to be, but generally have them at 30%. I am in Cost Savings mode, Export Solar, No Grid Charge.

I do have a $0.03 differential between my buy and sell prices for each period, but even before putting that in it still charged to 100% before peak.
 
Another solution to this issue might be "export everything." Given the difference between part-peak and peak rates in EV-A, that should make it charge during the part-peak period before discharging at 2pm. This might not be ideal if you're a net producer, but maybe you could adjust the backup reserve to avoid dumping too much extra energy to the grid.

EV2-A does not trigger this kind of behavior since most of the day is off-peak, not part-peak. This means that the Powerwalls take all the solar until 3pm or they're fully charged. With "export everything," they charge until 4pm if needed and then discharge during peak until they're back down to reserve.
 
Last edited:
I'm grandfathered on to EVA not EVA2
When you all say you are on EVA is that EVA the original, or EVA2? I am on EVA the original and have two PWs and the only time my PWs don't fill to 100% is on Fridays, and sometimes on Thursdays. I move my reserve from 30% to 50% depending on how risky I want to be, but generally have them at 30%. I am in Cost Savings mode, Export Solar, No Grid Charge.

I do have a $0.03 differential between my buy and sell prices for each period, but even before putting that in it still charged to 100% before peak
 
If I understand correctly, then it is only an issue if you're not to fully charge your powerwall before mid peak rates begin.
correct - so it was only an issue on week days and not weekend (no mid-peak on weekends)

but the core issue/lesson seems to be that where mid-peak rate periods are involved the system will only charge enough to cover anticipated/predicted peak usage - once it has a "enough" in the bank to cover the upcoming peak consumption period it will stop charging the batteries and let excess solar flow the grid…

in my case based on my normal/predicted peak usage it would tend to only charge the system to 75%-80% - and then stop charging and sell the rest of the power to the grid…

that meant two thing
  1. I would only "enter" the peak period with 75-80% battery
  2. I would always "exit" peak at 50% (9 pm)
this would leave me with only 50% for the overnight run to handle any outages from 9 pm until about 8 am the next day

since making the change to my TOU schedule (removing week day mid-peak TOU rate periods from the schedule)

I'm now entering the the "peak" TOU window w/100% battery - exiting peak with 70-80% battery for overnight…and because I'm not "scraping" bottom on my reserve limit I've now set my reserve to the recommended "min" of 20%

the way Tesla has it setup now is kinda of a perverse incentive - if I had it set to 20% and still had "mid-peak" TOU windows the whole system would only ever be charged to about 50-60% capacity M-F - and I'd spend every night at 20% battery for a 11 hour stretch with only 20% battery to deal with outages until the morning when solar would kick in…

I'm not sure I'd make the same engineering decisions on this sort of policy if I was designing the algorithms…

for my personal tastes I much prefer my current policy with the no-mid-peak work around - but now I no longer get proper "mid-peak" acurrals for the solar benefit cost analysis in app…
 
by removing the mid-peak TOU billing period I now have the "policy I want"
  • I enter the "peak" period at 100% capacity
    • assuming there was enough solar from 7 am to 3 pm to achieve that - normally the case
  • typical week day nights I use 20-30% capacity to "defend" my home from PG&E peak rates
  • this leaves me with 70-80% overnight for outages
    • vs. 50% prior to this change
  • _BUT_ for the occasionally "peak" over-run the system has "authority" to use upto 80% full capacity (20% reserve) for "peak-defense" - but this should be infrequent given typica/actual usage
with my settings now I prioritize capacity for outages - while still having a "healthy" budget for peak-defense…

basically with Tesla's default mid-peak policy it will choose to leave outage/backup capacity un-used to sell kWh's to the grid

I much prefer full capacity with some cost savings…
 
I've had a "behavior" with my Powerwalls recently - and today after a very helpful chat session with an excellent Tesla support representative I now fully understand what was/is going on and how to work around it.

Problem/Behavior Statement: My system was not fully charging my Powerwalls on a daily basis - it was cutting "off" my battery charging and leaving the Powerwall system @ 70-85% capacity even though I had plenty of solar production to "fill up" the batteries. This was frustrating me - because we have a lot of outages in our area and I want my batteries to be top capacity so that I have plenty of power for our outages.

My Settings: Time based Controls - 50% backup capacity - w/PG&E EV-A rate schedule "entered" in the system with full off-peak, mid-peak, peak TOU rate windows entered for both week days - and weekends and the two "seasons".

what I found out…

with "Time Based controls" the powerwalls develop a history/prediction of how much power is going to be used during "peak" - during the off-peak/mid-peak rate period the Powerwall software will endeavor to optimize to only charge the Powerwall system enough above my 50% setting to make it through the peak period and "land" back at 50% capacity as it "exits" the peak power TOU rate time window. The "excess" solar produced during the mid-peak TOU-rate-time-window will be pushed to grid for NEM credits rather than used to top-off the batteries.

solution to this "problem/behavior" - in working with the Tesla phone support representative - we decide to "lie" to the Powerwalls about the TOU rate period and I removed the "mid-peak" TOU-time-windows and now my TOU schedule only contains "off-peak" and "peak" TOU-rate-time windows. In implementing this "work around" I have now seen an immediate change in behavior and the Powerwall system now uses as much "off-peak/mid-peak" solar production as it can to fill the batteries (my goal) - rather than "stopping" at the predicted capacity required to provide sufficient power for the predicted "peak" consumption time-window on the same day.

now that I understand the problem I can see why/how the Powerwall does this - but this behavior is not my preference as I have the powerwalls for backup given numerous outages in our area - but I also like to use the Powerwalls to "defend" my home and NEM bill against PG&E "peak" rate periods with my own solar and battery power.

I want to use my power to defend again "peak" rates, but not be forced to then live overnight at what ever "min" % I've selected - charge to 100% every day - and use what you need to for peak - but most of the time I want as much power as I can have for overnight - not 50%+peak-usage charging target - and always 50% overnight…

the solution of excluding "mid-peak" from the rate-schedule is an acceptable work around in my opinion - but less than ideal.

Problem: why isn't my powerwall filling up everyday when there is plenty of off-peak/mid-peak solar to provide sufficent power to top-off the batteries?
Reason: the powerall is trying to only harvest "enough" solar power from mid-peak to "meet" predicted consumption for peak on that date/day-of-week- and sell the "excess" back to grid at mid-peak rates
Solution: adjust your powerwall rate schedule mid-peak TOU time windows to reflect your personal preference about when you wouldn't mind selling mid-peak solar power to grid rather than using that power to charge your batteries.
  • I understand what the Powerwall is doing now.
  • I can see that someone might want it to behave that way and it's quite clever
  • But it's not my personal perference for how it should behave - so for now I've removed my mid-peak TOU-time-windows
NOTE: in reviewing my history you can see how well the predictions do in terms of history - ie.e if you look back in time at your energy graphs - you can review on what days your battery "cut off" before the end of the peak-rate period and you used solar/grid power to "finish" the peak rate period - in reviewing my data - the system's predicxtions are accurate most of the time and it actually does a really really excellent job of predicting peak power usage and what amoutn of power it needs to dump into the batteries to cover your peak usage, there by maximizing the available power to sell during mid-peak from "excess" solar…

so kudos to Tesla for coming up with this really clever behavior - but alas it's not my perference as to how it shoudl behave.

mostly I don't like "exiting" the peak rate period (9 pm most days) at 50% battery - I'd rather "exit" the peak rate period time-window with as much power for overnight for an outage - rather than the target "minimum backup" amount

also now that I understand this - I'm comfortable adjusting the minimum backup lower - 25% - because I know on most nights 25-30% will cover my peak usage window - but if I let Tesal manage it - it would only ever charge my batteries enough to cover peak time window and land back at 25% - which isn't very outage friendly…

I share this in the spirit of what I learned today- apologies if everyone else already understood this - but you learn something new every day - and this was my item for today.
I don't understand the logic of not fully charging the Powerwalls during off-peak periods. It seems that once you've fully charged the Powerwalls, if you had the same throughput on subsequent days that everything would be the same other than the higher level of charge. What is the advantage of leaving room for additional charging?
 
I don't understand the logic of not fully charging the Powerwalls during off-peak periods. It seems that once you've fully charged the Powerwalls, if you had the same throughput on subsequent days that everything would be the same other than the higher level of charge. What is the advantage of leaving room for additional charging?
Partial peak begins at 7AM on the EV-A rate schedule. That was one of the big changes in the EV2-A rate. The Powerwalls optimize for exporting as much as possible in all rate periods other than off-peak. That's why they only charge as much as they think necessary to cover peak during the partial peak period.

@dortor4ev - do you have access to the "Export Everything" option? I think financially this could have the same effect you want without having to "lie" about the rate structure. The Powerwalls would charge to 100% and then discharge to the reserve every day. You could pick your reserve to be the level at which you feel safe overnight.
 
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Partial peak begins at 7AM on the EV-A rate schedule. That was one of the big changes in the EV2-A rate. The Powerwalls optimize for exporting as much as possible in all rate periods other than off-peak. That's why they only charge as much as they think necessary to cover peak during the partial peak period.

@dortor4ev - do you have access to the "Export Everything" option? I think financially this could have the same effect you want without having to "lie" about the rate structure. The Powerwalls would charge to 100% and then discharge to the reserve every day. You could pick your reserve to be the level at which you feel safe overnight.
OK, understand now, thanks. I'm on EV2-A and partial peak doesn't start until 3pm.
 
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aesculus

Still Trying to Figure This All Out
May 31, 2015
4,967
2,892
Northern California
Partial peak begins at 7AM on the EV-A rate schedule. That was one of the big changes in the EV2-A rate. The Powerwalls optimize for exporting as much as possible in all rate periods other than off-peak. That's why they only charge as much as they think necessary to cover peak during the partial peak period.

@dortor4ev - do you have access to the "Export Everything" option? I think financially this could have the same effect you want without having to "lie" about the rate structure. The Powerwalls would charge to 100% and then discharge to the reserve every day. You could pick your reserve to be the level at which you feel safe overnight.
It might not be as simple as that. Depends on a lot of factors. You can see my example here:

 
It might not be as simple as that. Depends on a lot of factors. You can see my example here:

NEM 1.0 simplifies the issue quite a bit, though, because NBCs are not an issue. I'm assuming NEM 1.0 because of the EV-A grandfathering. The idea would be to pick a reserve that doesn't result in over-exporting (i.e. exporting beyond the point where there is financial gain). If NBCs are not a consideration, it should be possible to adjust the reserve to generate equivalent NEM credits at True-up with "export everything" as using "export solar only" with the adjusted rate schedule.
 

aesculus

Still Trying to Figure This All Out
May 31, 2015
4,967
2,892
Northern California
NEM 1.0 simplifies the issue quite a bit, though, because NBCs are not an issue. I'm assuming NEM 1.0 because of the EV-A grandfathering. The idea would be to pick a reserve that doesn't result in over-exporting (i.e. exporting beyond the point where there is financial gain). If NBCs are not a consideration, it should be possible to adjust the reserve to generate equivalent NEM credits at True-up with "export everything" as using "export solar only" with the adjusted rate schedule.
Yes, those lucky not to have to deal with NBCs. I am still grandfathered into EVA but had to take NEM 2.0 to keep it. And I still only have a few years of life left before they kick me to somewhere else. :(
 

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