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What Factors does Cost Saving Mode Take into Consideration?

h2ofun

Active Member
Aug 11, 2020
1,598
259
auburn, ca
The problem with that is there's no "scheduled Self-powered" mode and you might run out of battery before or during peak and then pull from the grid and pay peak rates.

In order to power my house off-grid as much as possible, I use Balanced but set the shoulder period to be much longer, such as 7 pm until 3 am. I then have off-peak start at 3 am instead of 7 pm and only last for a couple hours. This way, I really only use grid power for a few hours a day and the peak period is always covered by Powerwalls.
I have my peak 3 to 1am. Off peak, 1 am to 3pm. But, when I get up, most of the time house still 100% being run off the batteries. So I see no reason to use a shoulder. It seems to have the smarts to know how much battery I use, how fast solar will charge, and for me, just keeps me on battery until solar kicks in. Fun to watch, Now, I do not have my heat pumps running which makes a HUGE difference. Luckily my heat pumps are on a separate GW from the house so I have total flexibility
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,427
8,570
Colorado
I have my peak 3 to 1am. Off peak, 1 am to 3pm. But, when I get up, most of the time house still 100% being run off the batteries. So I see no reason to use a shoulder. It seems to have the smarts to know how much battery I use, how fast solar will charge, and for me, just keeps me on battery until solar kicks in. Fun to watch, Now, I do not have my heat pumps running which makes a HUGE difference. Luckily my heat pumps are on a separate GW from the house so I have total flexibility
Do you have a should period for ToU? We have an actual shoulder period as well. Basically, the way we have it set up, we only really use the grid during a few hours of off-peak. Solar and Powerwalls then always cover peak and usually cover all of the actual shoulder period.
 

h2ofun

Active Member
Aug 11, 2020
1,598
259
auburn, ca
Do you have a should period for ToU? We have an actual shoulder period as well. Basically, the way we have it set up, we only really use the grid during a few hours of off-peak. Solar and Powerwalls then always cover peak and usually cover all of the actual shoulder period.
At the moment, since I am on tou-c, there is peak/non peak. EVA-2 has a some shoulder, but since the cost is still much higher than non peak, I am just going to assume peak and shoulder are both the same. Makes it easy to program that way.

I have been able to get batteries and solar to cover just about everything , when the solar is working. (Not when my one inverter was bad the last week)
Not running heat pumps makes a huge reduction in need. I currently have 15K solar, would like to add another 10K. Will see if I can get a bid and approvals for this. I just want to load up my PGE back with as much 3x power as possible to cover winter.
 

astrorob

stealth performance M3
Aug 27, 2014
397
73
oakland, ca
I never considered that cost savings mode might actually take round trip losses into effect. My thought was more along the lines that it figured "I dont need full battery to make it through the defined peak period, XX is enough, so let me export solar for credit".

i guess why i thought this might be part of it is that they reduced the charging rate for 20-30 minutes as the target SOC was approaching. although i don't have any evidence for where the system might be most efficient, i feel like there at least has to be a reason why they did that. i know that as a battery gets full you sometimes reduce the charge rate due to the chemistry but i think over here even the max my PV system can put out is well below the max charge rate for a battery this size.
 
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tfan2018

Member
Apr 14, 2018
71
20
USA
My understanding of Balanced is one of the things it will do is allow the home to use solar power instead of grid power when the Powerwalls need to be recharged during off peak. Cost Saving will prioritize Powerwall recharging instead of solar home use during off peak. Once the Powrwalls are recharged, it will switch to allowing the home to use solar power during off peak instead of sending it to the grid.
Allowing the home to use solar during off peak should reduce NBCs.

why does it seem like balanced mode might actually end up saving more $ since it will reduce the need to pull power from grid and accrue NBCs? As long as PW is fully charged and able to supply all the power needed during peak it seems balanced would be best? Trying to figure out which mode will save the most $. I plan to get one powerwall only with 8.16kW system that is oversized
 

bob_p

Active Member
Apr 5, 2012
3,635
2,768
We are on a Free Nights plan - electricity is $.20/KWh from 9AM to 9PM and completely free from 9PM to 9AM.

In Cost-Savings mode, the PowerWalls discharge based on Tesla's prediction of how much net solar energy will be generated the next day, "making room" for re-charging the PowerWalls. While this algorithm seems to work fine most of the time, it's not always correct - and the next day the PowerWalls won't fully recharge before nightfall.

Since we have completely free electricity overnight, would prefer the system not discharge the batteries at all overnight - though that might have a negative impact on the battery life, if the PowerWalls are sitting at 100% charge for extended periods (which happens when Storm Watch has been activated).
 

RKCRLR

Member
Apr 13, 2020
285
106
Garden Valley, CA
I just switched to Balanced mode yesterday and things operated as expected. The Powerwalls discharged during peak hours and stopped discharging at midnight when I'm off peak.
However, this morning at 5am when the heat pump came on they started discharging again and are continuing to discharge even though I'm on off peak rates.
This is the exact opposite of what I want since I never want to be using the Powerwalls during off peak hours. It didn't do this in Cost Saving mode.
I'll leave it it Balanced mode for a while to see if it figures things out.
 

h2ofun

Active Member
Aug 11, 2020
1,598
259
auburn, ca
I just switched to Balanced mode yesterday and things operated as expected. The Powerwalls discharged during peak hours and stopped discharging at midnight when I'm off peak.
However, this morning at 5am when the heat pump came on they started discharging again and are continuing to discharge even though I'm on off peak rates.
This is the exact opposite of what I want since I never want to be using the Powerwalls during off peak hours. It didn't do this in Cost Saving mode.
I'll leave it it Balanced mode for a while to see if it figures things out.
Why not? This is how my setup is working. I do not want grid delivery charges. The batteries fully charge before peak. I only really want solar going back to grid during peak hours. I am off grid 95% of the time now. What could be better?
 

RKCRLR

Member
Apr 13, 2020
285
106
Garden Valley, CA
Why not? This is how my setup is working. I do not want grid delivery charges. The batteries fully charge before peak. I only really want solar going back to grid during peak hours. I am off grid 95% of the time now. What could be better?
1) I want to make the Powerwalls last as long as possible before they need to be replaced while still having a $0 True-up.
2) I want to maximize the reserve for power outages. If I were to loose power later this morning I'd have less time on the Powerwalls if the sun was obscured.
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,427
8,570
Colorado
I just switched to Balanced mode yesterday and things operated as expected. The Powerwalls discharged during peak hours and stopped discharging at midnight when I'm off peak.
However, this morning at 5am when the heat pump came on they started discharging again and are continuing to discharge even though I'm on off peak rates.
This is the exact opposite of what I want since I never want to be using the Powerwalls during off peak hours. It didn't do this in Cost Saving mode.
I'll leave it it Balanced mode for a while to see if it figures things out.
That's expected and is how our system works. Our goal is to reduce the amount of energy we take from the grid, not to avoid discharging in off peak periods. Our Powerwalls stop discharging exactly when we expect and they will start discharging later if they still have sufficient SoC right before sunrise. If we raise the reserve, then they won't start discharging in off peak since they will have already been drained to the reserve limit.

1) I want to make the Powerwalls last as long as possible before they need to be replaced while still having a $0 True-up.
2) I want to maximize the reserve for power outages. If I were to loose power later this morning I'd have less time on the Powerwalls if the sun was obscured.
If your goals are to not discharge in off peak then maybe you should stick with Cost Saving mode. You could also bump up the reserve so that the Powerwalls don't drain past the higher SoC.
 
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h2ofun

Active Member
Aug 11, 2020
1,598
259
auburn, ca
1) I want to make the Powerwalls last as long as possible before they need to be replaced while still having a $0 True-up.
2) I want to maximize the reserve for power outages. If I were to loose power later this morning I'd have less time on the Powerwalls if the sun was obscured.
Good luck, I think they are working great. The PW's will last just fine. I am not worried about power outages during the non winter.
 

h2ofun

Active Member
Aug 11, 2020
1,598
259
auburn, ca
That's expected and is how our system works. Our goal is to reduce the amount of energy we take from the grid, not to avoid discharging in off peak periods. Our Powerwalls stop discharging exactly when we expect and they will start discharging later if they still have sufficient SoC right before sunrise. If we raise the reserve, then they won't start discharging in off peak since they will have already been drained to the reserve limit.


If your goals are to not discharge in off peak then maybe you should stick with Cost Saving mode. You could also bump up the reserve so that the Powerwalls don't drain past the higher SoC.
I have my reserve set at 10%. Why would I want it any higher?
 
Mar 15, 2021
61
29
California
I just switched to Balanced mode yesterday and things operated as expected. The Powerwalls discharged during peak hours and stopped discharging at midnight when I'm off peak.
However, this morning at 5am when the heat pump came on they started discharging again and are continuing to discharge even though I'm on off peak rates.
This is the exact opposite of what I want since I never want to be using the Powerwalls during off peak hours. It didn't do this in Cost Saving mode.
I'll leave it it Balanced mode for a while to see if it figures things out.
Yes. PW will discharge during off peak at times to make room for solar based on your usage, production, and reserve level.
 

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RKCRLR

Member
Apr 13, 2020
285
106
Garden Valley, CA
Good luck, I think they are working great. The PW's will last just fine. I am not worried about power outages during the non winter.
The main reason I got the Powerwalls was for backup. My solar is sized (in KWh) to equal my consumption. The power is very unreliable where I live. I just had a brief power outage two day ago.
 

h2ofun

Active Member
Aug 11, 2020
1,598
259
auburn, ca
The main reason I got the Powerwalls was for backup. My solar is sized (in KWh) to equal my consumption. The power is very unreliable where I live. I just had a brief power outage two day ago.
One reason I am lucky to have 5 PW's. I do not even have to think about PW level for most of the year. I oversized my solar, and am trying to even oversize it more. I just do not want to have to play with stuff all the time. I just do not want to have to think about it. Would be cool if I can get 100 panels on my roofs and maybe 25KW.
 
Mar 15, 2021
61
29
California
The main reason I got the Powerwalls was for backup. My solar is sized (in KWh) to equal my consumption. The power is very unreliable where I live. I just had a brief power outage two day ago.
If that's your main goal, then backup mode would be best. Or if you have a TOU plan, then cost savings will be best.

I wouldn't worry about leaving your batteries at 100%. First they are not actually at 100%, and second if you have a TOU they will discharge during the peak and remain at that lower level until they charge again the next day (so they will be well under 100% most of the time.)
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,427
8,570
Colorado
I have my reserve set at 10%. Why would I want it any higher?
The Powerwalls will totally shut down when they go below 10%. From Best Practices During Power Outages | Tesla Support:

Running Low on Energy​

If Powerwall has less than 10% energy remaining, it will enter a standby state and stop providing power to your home. If your system is connected to the internet, you'll receive a push notification in the Tesla mobile app when Powerwall enters standby.

When in standby and paired with a solar energy system, Powerwall will automatically attempt to recharge from solar for six minutes every hour between 8 a.m. and 4 p.m. local time. If enough solar is available to charge Powerwall while still powering your home, this automatic charging will continue. Otherwise, it will wait for the next hour to attempt charging again.

So your Powerwalls aren't going to provide much backup at all if you have the reserve set that low. Two years ago, we had a 48 hour outage. We had enough solar and Powerwall charge to make it through the first 24 hours but on the second day of the outage, the Powerwalls went below the 10% limit and shut off. They then tried throughout the day to restart but they couldn't keep the solar going consistently through the day because of the inverter and gateway settings and extreme cold temperatures. They have since updated the firmware so hopefully that won't be an issue in the future. We've had multiple 48 hour outages over the past few years and even with 4 Powerwalls, a 10% reserve (if usable) wouldn't even last us through the night. We set our reserve slightly higher in the winter so that it will cover us from sunset to sunrise. That way, if the power goes out while we don't have solar, our Powerwalls will be able to get us through the darkness until the sun comes up the next morning.
 

h2ofun

Active Member
Aug 11, 2020
1,598
259
auburn, ca
The Powerwalls will totally shut down when they go below 10%. From Best Practices During Power Outages | Tesla Support:


So your Powerwalls aren't going to provide much backup at all if you have the reserve set that low. Two years ago, we had a 48 hour outage. We had enough solar and Powerwall charge to make it through the first 24 hours but on the second day of the outage, the Powerwalls went below the 10% limit and shut off. They then tried throughout the day to restart but they couldn't keep the solar going consistently through the day because of the inverter and gateway settings and extreme cold temperatures. They have since updated the firmware so hopefully that won't be an issue in the future. We've had multiple 48 hour outages over the past few years and even with 4 Powerwalls, a 10% reserve (if usable) wouldn't even last us through the night. We set our reserve slightly higher in the winter so that it will cover us from sunset to sunrise. That way, if the power goes out while we don't have solar, our Powerwalls will be able to get us through the darkness until the sun comes up the next morning.
I really am not worried about backup. Meaning we usually get warnings ahead of time if PGE is going to cut for wind and fire. Solar charges them back pretty fast. With 5, I have lots of capacity. I have a generator if they do go dead. Since my PW's are on 2 gateways, I really have 2 systems installed, so I at worst case can run an extension cord from one setup thats working to the dead part, if I want to. Everyone has a different reason they bought this stuff. I just am trying to not let it control me anymore than it already is. The longer I have it, the more I see I can just ignore, until something breaks like one of my inverters just did.
 

RKCRLR

Member
Apr 13, 2020
285
106
Garden Valley, CA
If that's your main goal, then backup mode would be best. Or if you have a TOU plan, then cost savings will be best.

I wouldn't worry about leaving your batteries at 100%. First they are not actually at 100%, and second if you have a TOU they will discharge during the peak and remain at that lower level until they charge again the next day (so they will be well under 100% most of the time.)
When I put the solar in I has on a tiered plan and sized it for $0 true up. I later got the Powerwalls through SGIP for backup but one of the conditions was I switch to the EV2a TOU plan. I didn't realize how drastic EV2a was and now need to use the Powerwalls during peak hours to still obtain a $0 true up.

I'm not concerned about leaving the Powerwalls at 100% and they get exercised daily anyway. But the 37.8MWh throughput rating tells me they are cycle limited so the less I use them the longer they should last.

Yea, I'll probably switch back to Cost Saving mode and play with the reserve/peak hours to target the $0 True-Up while maximizing winter reserve.
 

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