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Better to use powerwalls or grid as my daily storage?

GuyHall

Member
Jan 16, 2014
234
60
Granite Bay, CA
Just got my pto and I'm trying to decide the best way to use my powerwalls (3) and solar. I'm expecting to generate more than sufficient power over the year to meet our needs. Should I fill the powerwalls during the day and draw from them at night? Or, keep them in backup mode and use the grid as my storage?
 

aswami

Member
Feb 12, 2021
54
24
Phoenix
I have set my Powerwall to cost saving mode and it seems to be working exactly as I want it to work - Powerwall energy is drawn only during on-peak hours. Grid energy is drawn at all other times. My off-peak energy cost is lower than the cost at which my utility buys back my excess solar generation. So, I don't want to draw any Powerwall energy and use as less of solar as possible during off-peak hours.
 
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jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
7,810
8,638
Riverside Co. CA
Just got my pto and I'm trying to decide the best way to use my powerwalls (3) and solar. I'm expecting to generate more than sufficient power over the year to meet our needs. Should I fill the powerwalls during the day and draw from them at night? Or, keep them in backup mode and use the grid as my storage?

The answer to this kind of question depends on why you purchased them in the first place, and what you would like. Are you trying to be more independent from the grid? Have the most power available in case of a power outage because the grid is unstable where you are? Reduce usage of time of use peak rate power?
 
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GuyHall

Member
Jan 16, 2014
234
60
Granite Bay, CA
Good questions. Primarily purchased PWs for protection from power outages, though I'd like to help mitigate duck curve impacts.

I'd like to avoid usage that will shorten the life of the pws. What behaviors will lengthen the life of the pws?
 

jrweiss98020

Tessa's Tesla
Jan 9, 2020
413
291
Edmonds, WA
Since you can't control the maximum state of charge, just avoid going too low. If you go self-powered, don't go below 25%.

As for your initial question, there are some losses in the charge/discharge cycle, so Backup Only mode is the most efficient. I use that most of the time, going to self-powered occasionally to test the system.

If you have Time of Use billing, use the Powerwalls during peak pricing.
 
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h2ofun

Active Member
Aug 11, 2020
1,678
273
auburn, ca
Good questions. Primarily purchased PWs for protection from power outages, though I'd like to help mitigate duck curve impacts.

I'd like to avoid usage that will shorten the life of the pws. What behaviors will lengthen the life of the pws?
What TOU rate plan are you on?
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,447
8,607
Colorado
Since there is no "scheduled" Self-powered mode, we use TBC-Balanced and set a schedule so that our Powerwalls and solar power the house 20+ hours a day. Ours always kick in at 3 pm and power the house until 3 am. We then use grid power exclusively for a couple of hours at off-peak rates. Then our Powerwalls usually kick in again (assuming sufficient SoC) until solar takes over powering the house and charges the Powerwalls back up.

You can always set the reserve high if you want to ensure you'll have enough charge to make it through an outage.
 
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h2ofun

Active Member
Aug 11, 2020
1,678
273
auburn, ca
Since there is no "scheduled" Self-powered mode, we use TBC-Balanced and set a schedule so that our Powerwalls and solar power the house 20+ hours a day. Ours always kick in at 3 pm and power the house until 3 am. We then use grid power exclusively for a couple of hours at off-peak rates. Then our Powerwalls usually kick in again (assuming sufficient SoC) until solar takes over powering the house and charges the Powerwalls back up.

You can always set the reserve high if you want to ensure you'll have enough charge to make it through an outage.
I kinda do the same. I am TBC-balanced. I set peak from 3pm to 1 am. Set the PW's to 10%. But, the system seems to have learned what it needs to do. Meaning, most of the time it still is running the house 100% off grid when I get up in the morning, and continues, depending on what I turn on in the house. If I were to stay on TOU-c or d, I would probably just leave in back up mode since there is no real cost difference between peak and non peak. But EVA-2 is a total different beast, at just about 3x difference between peak and non peak as you know
 
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getakey

Active Member
Jan 28, 2020
1,052
333
95762
Just got my pto and I'm trying to decide the best way to use my powerwalls (3) and solar. I'm expecting to generate more than sufficient power over the year to meet our needs. Should I fill the powerwalls during the day and draw from them at night? Or, keep them in backup mode and use the grid as my storage?
I live near you. I have 3 PWs. I use cost saving mode, but in the winter I set my reserve to 75%. In the summer I lower the reserve to 33% unless the winds are high
 

h2ofun

Active Member
Aug 11, 2020
1,678
273
auburn, ca
I live near you. I have 3 PWs. I use cost saving mode, but in the winter I set my reserve to 75%. In the summer I lower the reserve to 33% unless the winds are high
Even with my reserve set to 10%, seems the smarts do not let the PW's even get close to this. Meaning, it starts pulling from grid, but I have no idea what logic it is using.
 

GuyHall

Member
Jan 16, 2014
234
60
Granite Bay, CA
Does your power go out that often, or you have critical electronics?
We decided for Solar and PWs when we had a fall with three 3-day power outages. We also were tired of watching every watt and wanted to just enjoy our home. Add to that a 3 EVs and a desire to electrify our stovetop, HVAC, and water heater. So we had a fair amount of uncertainty and decided to go big.
 

h2ofun

Active Member
Aug 11, 2020
1,678
273
auburn, ca
We decided for Solar and PWs when we had a fall with three 3-day power outages. We also were tired of watching every watt and wanted to just enjoy our home. Add to that a 3 EVs and a desire to electrify our stovetop, HVAC, and water heater. So we had a fair amount of uncertainty and decided to go big.
How big is your solar?

Luckily the 3 day outage was like 2 years ago and once.

Issue I am finding is how quickly can one recharge their PW's based on what use of them. And in the winter, well. I just made my house 99% electric, and the electric heat is a LOT of energy!! At the moment I see no way to have solar keep up with it charging the PW's in winter. Not sure what I will do with the EV2-a rates
 

GuyHall

Member
Jan 16, 2014
234
60
Granite Bay, CA
We're in PG&E territory using EV2 rates. Peak rate $0.50 and off peak $0.18. As I understand it, at the annual true up pge will look at the three rate buckets separately. Solar will generate more than enough to cover our all our off-peak kwh. So, we should use the pw to shift excess solar generated power to partial peak and off peak to ensure we don't have deficits in those.
 

GuyHall

Member
Jan 16, 2014
234
60
Granite Bay, CA
How big is your solar?

Luckily the 3 day outage was like 2 years ago and once.

Issue I am finding is how quickly can one recharge their PW's based on what use of them. And in the winter, well. I just made my house 99% electric, and the electric heat is a LOT of energy!! At the moment I see no way to have solar keep up with it charging the PW's in winter. Not sure what I will do with the EV2-a rates
As I understand it, the annualized true up combines the summer and winter power. If so, shifting generated power from off peak to peak during the winter is best even if one runs a winter off peak deficit. The over production in the summer off peak will offset any winter off peak deficits. I guess even if one didn't have any summer surplus, always shifting off peak to peak is a win.
 

GuyHall

Member
Jan 16, 2014
234
60
Granite Bay, CA
How big is your solar?

Luckily the 3 day outage was like 2 years ago and once.

Issue I am finding is how quickly can one recharge their PW's based on what use of them. And in the winter, well. I just made my house 99% electric, and the electric heat is a LOT of energy!! At the moment I see no way to have solar keep up with it charging the PW's in winter. Not sure what I will do with the EV2-a rates
So far this year we had a 21 hour outage. We only found out about it when PG&E texted us saying power would be restored in two hours, which raises the issue of draining the pws when a unrecognized outage occurs. We have 2 teslas for which I have to look into the Vehicle Charging during Power Outage option. However, the LEAF would have to be more closely watched.
 

jboy210

Supporting Member
Dec 2, 2016
4,849
2,982
Northern California
I have mine set to Advanced Balanced with the TOU Peak defined and Outage Reserve set to 30%. That provides good use of the battery to reduce pulling power from the grid, and does not let them get too low to not handle a minimum of 6 hours or so hours of outage. I will probably lower the Outage Reserve to 25% as we get closer to Summer.
 

GuyHall

Member
Jan 16, 2014
234
60
Granite Bay, CA
How big is your solar?

Luckily the 3 day outage was like 2 years ago and once.

Issue I am finding is how quickly can one recharge their PW's based on what use of them. And in the winter, well. I just made my house 99% electric, and the electric heat is a LOT of energy!! At the moment I see no way to have solar keep up with it charging the PW's in winter. Not sure what I will do with the EV2-a rates
Solar Roof system size: 21.98472 kW DC
Estimated gross annual electricity production for our Solar Roof in Year 1: 25,259 kWh
 

Redhill_qik

Member
Aug 16, 2020
144
70
South SF Bay, California
We're in PG&E territory using EV2 rates. Peak rate $0.50 and off peak $0.18. As I understand it, at the annual true up pge will look at the three rate buckets separately. Solar will generate more than enough to cover our all our off-peak kwh. So, we should use the pw to shift excess solar generated power to partial peak and off peak to ensure we don't have deficits in those.
I would set the PW to the Cost Savings with peak times from 4:00-9:00pm and shoulder/partial-peak from 9:00-12:00am and office ignore the 3:00-4:00pm partial peak as your solar should be cover most if not all of your usage.

Note: I couldn't get the app to go to 12:00am, it would only allow the shoulder bar to go to 11:30pm.
 
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