Question about configuring the Powerwall Advanced settings

2Intense

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I have a solar system as well as 4 Tesla Powerwalls and I am trying to come to terms with how I should be using Tesla's advanced mode option given my circumstances.
First let me explain. I am on a TOU (Time of Use) rate plan with the power company. I pay a peak rate of $.45 per KWh from 4PM-9PM and a standard rate of $.17 per KWh the rest of the time. The NESCR (Net Energy Surplus Compensation Rate), or rate that I get reimbursed for the excess energy I produce and send back to the grid about $.03 per KWh. (varies between $.02-$.03 depending upon month).

If I run in advanced mode and have it set for the house to shift to battery power between 4PM-9PM I am consuming power I produced from solar and avoiding the $.45 per KWH period. At 9PM the batteries cease providing power and the house switches back to the grid and when the sun comes up, excess power that my solar produces will flow to top off the batteries before going to the grid. Then once the batteries are full, the overage goes back to the grid. My solar produces @ 85KWh of energy per day and consume @65 KWh per day. It's notable that about 50% of my consumption occurs during the peak period of 4PM-9PM.

So, basically I avoid paying the $.45 per KWH for 5 hours a day and of course lose the $.03 per KWH for the energy going into recharging my Powerwalls. (I know there's another 10% loss due to the AC/DC conversion process but again that would be computed at the $.03 rate). This seems like the best way to go, right?

Or,

Should I have it set to run all night? Come on at 4PM to avoid Peak rates and continue to run until 4, 5, 6, or 7AM and use all of my daily excess KWh and a large portion of my Solar to recharge the batteries during the day at the $.17 rate?

Setting aside the cycles on the batteries, how should I be doing this to optimize cost savings?
 

Ed Woodrick

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What is your intent? Are you solely trying to reduce the cost of electricity? Are you trying to provide power back in case of power failure? Or something else?

You need to watch and see how much power you use during the 4-9PM period. Is it more than the batteries can provide?

You really need to look at the amount of power that you use per hour on average and possible per season. Your power company may have the information for you.

I believe that the general thoughts are to kick on the batteries at 4 and run until you get down to a reserve percentage. The reserve is in the case of a power failure.
Determine the amount of solar that you can produce and then determine how long it will take to recharge the batteries. Make sure that the batteries can be fully charged, even on cloudy days, by 4PM.
 

2Intense

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What is your intent? Are you solely trying to reduce the cost of electricity? Are you trying to provide power back in case of power failure? Or something else?

You need to watch and see how much power you use during the 4-9PM period. Is it more than the batteries can provide?

You really need to look at the amount of power that you use per hour on average and possible per season. Your power company may have the information for you.

I believe that the general thoughts are to kick on the batteries at 4 and run until you get down to a reserve percentage. The reserve is in the case of a power failure.
Determine the amount of solar that you can produce and then determine how long it will take to recharge the batteries. Make sure that the batteries can be fully charged, even on cloudy days, by 4PM.
Yes, intent is solely reduce cost and I set aside 20% of the storage for back-up. I have been running the battery in advance mode with it set to take over from 4PM-9PM for the last few days and at 9PM when I return to grid power I am sitting with @65% of my battery left. which is why I raised the question, should I keep going. By 9PM, on weekdays anyway, we are about to pack it in and the TVs and lights, etc go off and I suspect the batteries could probably handle things until 4-5AM if I let them run. I have all of my consumption data readily available via a download from my power company and my system produces significantly more than I consume. I have 43ea 435w panels and I produce 1800-2700 KWh per month and my consumption is from 1200-1600KWh per month (low figure winter/cloudy, high figure spring/summer sunny).
 

Ed Woodrick

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If you are producing more than you are earning, why are you worrying about switching back to external power?
 

2Intense

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If you are producing more than you are earning, why are you worrying about switching back to external power?
To offset a portion of the consumption during PEAK rate period with stored power to reduce cost further.
 
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Bigriver

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@2Intense, I’m also missing something in the basic question.

My understanding is that on an average basis your production is higher than your consumption by a pretty nice margin. You have Powerwalls with about 50 kWh of capacity, but arguably don’t ever want to use all of that, as you want to maintain a reserve for power outages. You said that if you run on Powerwalls overnight that they will last until about 4 to 5 am. Thus you would have a few hours of having to pay $0.17/kWh until solar production comes back online and can meet your consumption. Wouldn’t this always be preferable, to have a few hours at $0.17/kWh than about 10 hours at that rate? With your eco system being that you pay $0.17/kWh or $0.45/kWh vs getting paid $0.03/kWh, don’t you always want to be using your own energy, only resorting to the grid when necessary, with priority of avoiding the peak rate?

Of course that is all in the average, and I know for me the devil is in the detail that not many days are average. I have day to day variations and season to season variations that would not give one answer. But my utility also credits me one for one with kWh sent to the grid with later pulling the kWh from the grid with no time of use factor. Thus, more and more I use the grid as if it were my very big Powerwall, saving my actual Powerwalls for backup. But for your situation, how often do you have a day where the Powerwalls would not get replenished enough to get you through the 4-9 pm peak period?
 

Ed Woodrick

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To offset a portion of the consumption during PEAK rate period with stored power to reduce cost further.
If you are producing 1800 kWh and using 1200 kWh. That suggest that you are using 24 kWh/day, only half of the battery pack. So I'm not sure why you would want to switch to the grid (except for quick recovery from low generation periods).

It sounds as if you can stay on battery 100% of the time. If you were using 1800 kWh and producing 1200 kWh, that would be another thing. But since you are producing more than you use. I'm really confused why you ever would switch to the grid. The grid is only there for selling excess power to.