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balanced costs saving mode config for offpeak; how to configure PW for "never discharge during this time / to this load"

sandyman44

New Member
May 25, 2021
1
0
United Kingdon
hi
I am in the UK, and use the Octopus Go Tariff, which has cheap electricity between 0030 and 0430. My 2x powerwalls have been installed since november 2020. They are backing up the whole house. I have 11kw of solar PV. I ran the PW system in cost-saving advanced mode since the second week . This meant that over the winter, the powerwalls would mostly charge themselves from grid during the offpeak period, and then discharge during peak, with a bit of help from winter solar. The mostly is the problem that I wish to discuss.

what happens if there is a day with a reasonable amount of solar (for a winter's day) , the PW will decide not to charge during the offpeak night period immediately following. The day after would inevitably be rainy, no solar, and thus the PW would run out of storage by mid-way through the 2nd day, thus making me use higher cost peak electricity. I've just added up the costs of the days where this happened, despite it only being a few days, they cost me more electricity than the rest of those months put together.

I of course setup my EV (non-tesla) to charge during this offpeak period, and to make matters worse, I find that the PW has discharged into the EV during offpeak. whereas I want both EV and PW to charge from grid whilst its cheap.

I've had discussions with tesla support about this - in my opinion, "advanced cost saving" mode, should have a default behaviour of "never discharge during the offpeak period". but it seems that is not the case - its very difficult to understand clearly what the defined behaviour is during that offpeak period - it seems to be "maybe charge, maybe standby, maybe discharge, depending on a number of factors that we won't tell you" - whereas for an end user it would be lot easier to work with if it was deterministic. At the very least, a settings tick box(es).

Furthermore, there should be a setting option for cost-saving mode to set a "charge from grid to this minimum level - during offpeak period". so that in winter you know you'd have enough cheap TOU stored for the day, regardless . If you get a bit more solar, then no big deal - that would be better than running out of PW and having to pay peak rate. tesla support have said that predicted next-day solar awareness is still not part of their software, so with variable weather, its a lottery.

I have tried working around this using home-assistant based automations, to send the change mode and change reserve level commands to the gateway based on timed scripts, which can provide something approximating to what I want, but its a real hassle and really should be integrated into the tesla software IMO.

there's also an option of course to rewire my incoming electrics so that I have a dedicated board upstream of the gateway that is outside its main CT, to supply the EV, but that is not ideal given that it should be possible to do in software, and doesn't take care of the "PW doesn't charge offpeak if previous day was sunny" problem.

anyone else seeing these issues?
thanks
Ian
 

Mark_T

Active Member
Nov 1, 2017
1,295
1,130
UK
I have tried working around this using home-assistant based automations, to send the change mode and change reserve level commands to the gateway based on timed scripts, which can provide something approximating to what I want, but its a real hassle and really should be integrated into the tesla software IMO.
As far as I am aware, that is as good as it gets right now...

The variability of UK weather was not a factor in the California based design :)

Not like the UK is alone in this need though, large parts of the USA do not benefit from California weather patterns either...
 

garrett5688

Member
Oct 7, 2017
579
1,019
DFW
I have the exact same complaints.

The only solution I have found is to raise the reserve level during off peak, and then lower it the next morning.

Another option is to toggle between self powered and backup only.

However with your off peak being only between 0030 and 430 this would be a huge pain for you.

what kind of automation have you found to work?
 

RKCRLR

Member
Apr 13, 2020
433
168
Garden Valley, CA
I use Cost Savings mode, have both my Peak and Part-Peak to start at 4 PM with my Peak ending at 9 PM and my Part-Peak ending at midnight.
I have never seen my Powerwalls discharge during Off-Peak. However, they will if I choose Balanced mode with the same time settings.
One difference I can see is I am not allowed to charge from the grid unless during Storm Watch.
 

miimura

Well-Known Member
Aug 21, 2013
6,362
6,065
Los Altos, CA
@sandyman44 you are in good company among your countrymen with Powerwalls. They are notoriously bad at dealing with the uneven UK weather. Unfortunately, the Advanced mode that Tesla provides isn't nearly advanced enough for it to always do what we want. I have long said that there should be additional options like the following:
- Never discharge during Off-Peak
- Charge to X% during Off-Peak (where grid charging is allowed, like UK & Australia)
- Shoulder is Self-Powered

In the meantime, I think the best you can do is to raise your Reserve when you think the following day will have inadequate solar generation. Even in California, I raise the Reserve according to the season so that the Powerwalls work the best with my small solar system.
 

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