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The important missing control for Tesla Powerwalls

I’ve had Powerwalls for four years now. As my thread title suggests, from experience, Powerwalls lack one very important, if not essential control; the ability to fill it to a given capacity. I’m pretty sure I’m not alone in the view given that many owners use the popular cheap but short off-peak tariffs which we have in the U.K.
I‘m fortunate in as much as from late spring to late autumn , I have sufficient solar capacity to keep mine filled up. I know that in the depths of winter I will need to fill up most nights from the grid. In the these two scenarios they perform pretty much on the money. Others probably struggle throughout the year.

However, late autumn and early spring have always been a nightmare. I had hoped that major changes to the Tesla app which included adding tariffs and reducing the operating modes to just self-powered and time based control would resolve the problems. But it didn’t. I’ve just switched to time based control for the winter and I’m stuck in the same annoying rut that happens every year!

Recently we in the U.K. have had the usual dull wet days and bright sunny days. Apart from being unusually warm. Autumn has been what it always is and the daylight hours get shorter.

In Time based control, Powerwalls depend upon their AI to work out how much of their power came from solar, how much they discharged and how much they need from the grid. That works reasonably in stable weather conditions. It fails abysmally when a few sunny days are followed by a dull day or two and vice versa. Furthermore, the AI has no idea that even if there is some sun coming, I want my Powerwalls topped up from the grid because I’ll be charging two EV’s from solar tomorrow.

Here’s the annoying part; on two separate occasions last week there was little solar, the first night PW’s were at about 50% at bedtime and one car was empty. I set my reserve to 47% knowing full well that I would have to wake myself up before 2.30am to check what was happening. I did and sure enough, the car had charged but the Powerwalls had only topped up to 62%. I did what I always do and upped the reserve to 75% as I knew that the following day would roughly produce enough to finish the job, which it did. Two days later, same thing. Set a higher reserve at bedtime, get up in the middle of the night to up the reserve again to ensure that they are full enough for the day.

I won’t set a final reserve at bedtime because then I’ll be buying peak rate power and I shouldn’t need to. No matter how good the AI is, it will never be better than me because it can never have my overview of my needs. The answer is simple; an optional slider control to set a charge level exactly the same as my Model 3. Why on on earth was that ever omitted? Perhaps it’s a USA thing. It’s obvious to me and I would get a good night’s sleep!
Does anyone else want a charge control added?
 
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Worked perfectly here. Dawn 'til dusk sunshine forecast for yesterday, so Powerwall only charged up from 37% to 47% overnight. Solar panels generated 20 kWh; enough for 3 laundry loads, 1 tank of hot water, and Powerwall at 90% by sunset.

Today's forecast is dawn 'til dusk murk, so Powerwall charged from 39% to 100% overnight of its own volition. My standby reserve is 15%.

It's got to be down to your recent switch from self-powered to time-based control.
 

Dilly

Active Member
Feb 24, 2020
3,486
3,129
Norfolk
Worked perfectly here. Dawn 'til dusk sunshine forecast for yesterday, so Powerwall only charged up from 37% to 47% overnight. Solar panels generated 20 kWh; enough for 3 laundry loads, 1 tank of hot water, and Powerwall at 90% by sunset.

Today's forecast is dawn 'til dusk murk, so Powerwall charged from 39% to 100% overnight of its own volition. My standby reserve is 15%.

It's got to be down to your recent switch from self-powered to time-based control.
I made the switch about a fortnight ago I think. So it should be up to speed.
Earlier in the week we went from a grim day to a slightly sunny day and it topped up perfectly overnight. The same with two grim days on the trot.
I’ve always found that in the main, if it’s going to get it wrong, it’s sunny to dull days that fool it.
 
Worked perfectly here. Dawn 'til dusk sunshine forecast for yesterday, so Powerwall only charged up from 37% to 47% overnight. Solar panels generated 20 kWh; enough for 3 laundry loads, 1 tank of hot water, and Powerwall at 90% by sunset.

Today's forecast is dawn 'til dusk murk, so Powerwall charged from 39% to 100% overnight of its own volition. My standby reserve is 15%.

It's got to be down to your recent switch from self-powered to time-based control.
Yesterday was lovely and sunny but my PW filled to 100% overnight so a significant chunk of power was fed to the grid. Bit of a waste.
I’m trying not to interfere with the settings and let the AI “do its thing” but my experience has been that it’s not very reliable…
#firstworldproblems
 

Drew57

Active ember
Apr 4, 2020
1,616
1,963
Chester UK
I follow these PW threads with great interest because it's a product I've always wanted but until the sort of issues mentioned here are resolved I will have to put it on hold.

I am already a light sleeper and if I had to wake during the night to control charging I would often remain so for the remainder. One day I hope to see a fix.
 
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Yesterday was a good sunny day and everything got topped up from solar.
knowing today and tomorrow would be pretty dull, at bedtime, the Powerwalls were at 77% so I set the reserve at 74% to fill them.
at 4.15 am they only filled to 78% and by 8am were at 72%.
So much for AI !
This is why we NEED Tesla to give us an optional manual control, as an option for the PowerWall charging.
 
I follow these PW threads with great interest because it's a product I've always wanted but until the sort of issues mentioned here are resolved I will have to put it on hold.

I am already a light sleeper and if I had to wake during the night to control charging I would often remain so for the remainder. One day I hope to see a fix.
I wouldn’t be out off by this.
The powerwalls are still fantastic bits of kit, but it’s easy go down the “maximum efficiency” rabbit hole… :)
 

Dilly

Active Member
Feb 24, 2020
3,486
3,129
Norfolk
I didn’t manage to wake up in the night to check the Powerwalls. Reserve was set at 58%. It managed 85% by 1.30am and stopped charging.
We’ll get through the day but the Sunday roast and the dishwasher cycle will eat a fair bit.
There is a chance of a small amount of solar today but a dull day in prospect for tomorrow.
The AI has a lot improvement to make up before it can come close to my judgement!
Right now, it’s comparable to auto high beam on the car :mad:
At least in the depths of winter it manages OK
 
The AI has a lot improvement to make up before it can come close to my judgement!
Looking back at our logs (HomeAssistant and a home-brewed logger), our Powerwall took around 6-8 weeks to start (mostly) doing the right thing after we got on the Go tariff at the end of Jan '22 and switched to time-base control mode. Like you, I spent a good portion of those 6-8 weeks cursing the PW for failing to download enough electrons overnight to see us through the next day. Since around the start of April, however, it hasn't let us down, as can be seen here:

screenshot.png


The drop in peak grid usage from April onwards is striking. Sadly, we'll never get it to zero - our PW is restricted to 3.68 kW charge/discharge by DNO edict, so cooking will easily max it out.
 
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Looking back at our logs (HomeAssistant and a home-brewed logger), our Powerwall took around 6-8 weeks to start (mostly) doing the right thing after we got on the Go tariff at the end of Jan '22 and switched to time-base control mode. Like you, I spent a good portion of those 6-8 weeks cursing the PW for failing to download enough electrons overnight to see us through the next day. Since around the start of April, however, it hasn't let us down, as can be seen here:

View attachment 871647

The drop in peak grid usage from April onwards is striking. Sadly, we'll never get it to zero - our PW is restricted to 3.68 kW charge/discharge by DNO edict, so cooking will easily max it out.
How can the DNO possibly have a say on the discharge rate to the house?? Fair enough to say you can’t feed the grid at more than x kWh but to decide how much of your own battery you can use in your own home with no impact on the grid seems either a misunderstanding or just plain stupid.
 
How can the DNO possibly have a say on the discharge rate to the house?? Fair enough to say you can’t feed the grid at more than x kWh but to decide how much of your own battery you can use in your own home with no impact on the grid seems either a misunderstanding or just plain stupid.
If the Powerwall is discharging at, say, 5 kW into the house and that demand suddenly goes away, then for a short time the Powerwall will dump to the grid until its inverter reacts to the change in demand (in the order of milliseconds).

In conjunction with our 6 kW of solar working at full power, Western Power's argument is that this could, however briefly, raise the voltage on the local LV distribution network above the limit of 253 volts as well as lead to a phase imbalance.

According to Western Power, we have three options:
  • Restrict Powerwall to 16 amps charge/discharge.
  • Dig up our street to replace all the LV cabling between us and the transformer (we're at the end of the line, farthest from the transformer). Street is about 150 metres in length, with about 20 houses.
  • Run 3-phase to our house and distribute loads/generation evenly across all phases.
It does feel like they're being Jobs Worths for the sake of an extra 4 amps in a very hypothetical situation.
 
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If the Powerwall is discharging at, say, 5 kW into the house and that demand suddenly goes away, then for a short time the Powerwall will dump to the grid until its inverter reacts to the change in demand (in the order of milliseconds).

In conjunction with our 6 kW of solar working at full power, Western Power's argument is that this could, however briefly, raise the voltage on the local LV distribution network above the limit of 253 volts as well as lead to a phase imbalance.

According to Western Power, we have three options:
  • Restrict Powerwall to 16 amps charge/discharge.
  • Dig up our street to replace all the LV cabling between us and the transformer (we're at the end of the line, farthest from the transformer). Street is about 150 metres in length, with about 20 houses.
  • Run 3-phase to our house and distribute loads/generation evenly across all phases.
It does feel like they're being Jobs Worths for the sake of an extra 4 amps in a very hypothetical situation.
As my DNO has already allowed 5.1kW of export, they have insisted that an export limiter is put on our system now that we have an extra 4.7kW gross and 3.7kW net extra panels. I'll have no restrictions on charging and discharging 3 PWs (3rd due this month), but I've asked my installer to limit the charging and discharging to only 11kW as I'll have a problem with our single phase supply.
 
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As my DNO has already allowed 5.1kW of export, they have insisted that an export limiter is put on our system now that we have an extra 4.7kW gross and 3.7kW net extra panels. I'll have no restrictions on charging and discharging 3 PWs (3rd due this month), but I've asked my installer to limit the charging and discharging to only 11kW as I'll have a problem with our single phase supply.
That's interesting, and is something I should suggest to the DNO. Odd that they've never mentioned it as an option. I'd be happy with them slapping an export restriction on our solar if it allowed the Powerwall to be derestricted.
 
That's interesting, and is something I should suggest to the DNO. Odd that they've never mentioned it as an option. I'd be happy with them slapping an export restriction on our solar if it allowed the Powerwall to be derestricted.
The cost of fitting the export restriction is about £400, and what pisses me off is that I will never export over 3kW, let along 5kW. Last month, as in the previous 3 months, I never exported more than a few kWh each month, and I resent giving them even 2kWh.
 

Vostok

Active Member
Jul 1, 2017
2,760
3,279
Sydney
Interesting discussion. I too have wished for additional PW2 controls via the app, because like many here, the “AI” in TBC mode seems imperfect at best. I don‘t like it’s ‘black box’ nature where it does weird things and you have no idea why. Like when during the day, PW2 might stop charging at 70% and excess solar is exported to the grid instead of charging PW2. WTH?

I have a small roof hence small solar array (5.8 kW) that doesn’t, on average, generate enough to offset household consumption. Even though I‘m in sunny Australia 😄. So I wanted more control over PW2 to optimise the cost of grid consumption. I keep all the 5-minute data from PW2 so I can do ”what if” analyses and try different algorithms to see what optimises costs.

And I found the addition of two simple toggle controls in the App would actually be very effective and work better in optimising costs than TBC (at least in my case):
  • Do not discharge PW2 during off-peak grid periods
  • Fully charge PW2 during off-peak grid periods
The second control obviously overrides the first, and is more aggressive in how much power PW2 retains for shoulder and peak periods.

I implemented these controls using the Telsa API and am running it as a cron job on my server. For the first control, it simply sets the “reserve percentage” of the PW2 to be equal to whatever the current charge state is at midnight (or whatever time you want to set), then returns it to 10% (or whatever level you want) at 7am. For the second control, it sets the reserve percentage to be 100% at midnight, which forces the PW2 to charge off the grid using offpeak electricity.

The effect of the first control is to have more stored electricity, on average, available for shoulder and peak periods, in the hope that it is enough to see you through the day until the next offpeak period starts.

It’s only been 2 weeks so far, and I currently only use the first control to see how well it works, but it is brilliant. 100% of our grid electricity usage has been off-peak in those 2 weeks. Not a single electron at other times. This is particularly important as my peak grid rate per kWh is nearly 4x my offpeak rate, so it should save me a decent amount of money. And with 2 x EVs, we don‘t want overnight charging to suck the PW2 dry when that power is more valuable to keep for the next day.

Based on the 2 weeks so far, it seems I would not need to activate the more aggressive second control. For those who have a bigger gap between solar production and consumption, the second control might be useful. It might be useful for me in winter months but we’ll see - easy enough to code different settings at different times of the year 😄

If you‘re lucky enough to have a big roof and solar production on average exceeds your household consumption, you probably would not need or want controls like this.
 
Yesterday the forecast was wall-to-wall sunshine today, and it was, with me generating 17.8kWh. However, anticipating the AI would not work, I turned off the immersion heater that is used during the GO period, but still the PWs charged to 100%. The lowest they got to in the morning was 81% before they started charging, so I had to heat the water and charge a car to prevent surplus going to the grid. I'm now at 71% and expecting the PWs to charge to 100% again tonight despite a similar wall-to-wall sunshine forecast.

This is where we need manual control over the PW charging, as I would have set mine to 75% last night and tonight.
 
If you are on ToU and want to charge to 100% overnight just set the off peak rate to 1p as well as the export.

I have done this at the start of October and had 100% charge every night. Good for peace of mind, especially living in Cornwall as the forecast is often wrong.

You can also quite easliy change the 3.6kw limit to 5.0kw in the engineer wizard by changing the Power supply to G99 ;)

Screenshot_20221127_170049_Tesla.jpg
 
If you are on ToU and want to charge to 100% overnight just set the off peak rate to 1p as well as the export.

I have done this at the start of October and had 100% charge every night. Good for peace of mind, especially living in Cornwall as the forecast is often wrong.

You can also quite easliy change the 3.6kw limit to 5.0kw in the engineer wizard by changing the Power supply to G99 ;)

View attachment 878798
How do you perform this change, sorry? :)
 

WannabeOwner

Well-Known Member
Nov 2, 2015
7,245
4,002
Suffolk, UK
How do you perform this change,

Settings
PowerWall
Utility Rate Plan (below "Time-Based Controls")

Scroll down to SCHEDULE - the first EDIT is for the periods (change them if you need to) and the second is for PRICING

Pricing Edit PAGES through the various SEASONS you may have set up (I only have one, I expect you too probably)

Click on the BUY rate for OFF PEAK ...

... I have just seen that I have a Self Generated Rate for Off Peak too ... good luck on that at 3AM !!
 

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