Powerwall Overnight Charging Rate

[mw963]

We've had a Powerwall 2 for just over two years, and for the first eighteen months (until March 2023) we had five hours per night of cheap rate electricity on the Octopus "Go Faster" tariff. Throughout that period - when using Time Based Control - our Powerwall would charge at a rate of 3.7 kW, which I've read several times is the optimum charging rate.

Since March 2023 Octopus have withdrawn "Go Faster" and the only similar tariff is "Go", which only has four hours a night of cheap rate electricity. I reset our app time settings, and since then our Powerwall charges at 5 kW on TBC.

I am concerned that this is putting unnecessary wear and tear on the battery. Even with only four hours a night avialable to charge economically, 3.7 kW would be a high enough rate (3.7 kW x 4 hours = 14.8 kWh, more than the capacity of the battery, so even if completely flat the battery could charge back up to 100% in four hours).

I contacted Tesla and was assured that 5 kW would not be harming the battery, although there seemed to be some hint of doubt in what they said about exactly why the maximum charge rate was being used instead of the optimum rate, with muttered talk of my possibly having having changed my "grid code" from P98 to P99 (I haven't of course). I think they said that 5 kW was indeed unusual and only for installations with a P99 code, which I'm fairly certain doesn't apply to me.

I'm left feeling that my battery is being abused night after night unnecessarily. Does anyone have any advice? Has anyone found the same situation - after all there must be others who were like me bumped off Octopus Go Faster last March...?

Finally, I continue to seethe that there is no progress in giving us a "charge to x % tonight" option in the app. The algorithms continue to make duff decisions about how much to charge the battery and only I can really make an accurate assessment of tomorrow's weather and my power needs on a day to day basis. That gripe is of course fully discussed here:

Tesla: we need more control over our PowerWalls

Tesla, Today around 1PM, you can see I turned off my PowerWalls. Do you know why? Because I wanted to use more of my stored electricity during the evening when solar is not shining and use the solar energy available from the grid during the day during non-peak hours rather than fossil fuels...

teslamotorsclub.com

 

[jjrandorin]

I'm left feeling that my battery is being abused night after night unnecessarily. Does anyone have any advice?

I have no input on "why" your charging might have changed. As it pertains to this part, however, the feedback I have about grid charging at all is that Tesla has a different warranty on a tesla powerwall that is charged from the grid, vs one that is charged from solar.

The only reason that I can think of that would possibly be, is that there is some difference when charged from the grid. The only difference I can think of is sustained charge rate (as solar, over time, would scale up and down, while grid power, if on, would be a constant source.

If they are telling you it is because your grid code changed, perhaps tell them to change it to a grid code that charges at the rate you want?

 

[VeloSteve]

My two Powerwall 2+ units are charging at about 6 kW each every night at midnight. The rate is the same from then until 3 PM, so there is no reason to charge so fast. There really should be a setting for this, either in terms kW or time.

I even wonder if Tesla is asking for trouble with this approach. If thousands of customers charge at maximum rate at the exact same time, it is going to make the utilities want to do something about those load spikes. I'd rather self-regulate than be regulated.

 

[BGbreeder]

My two Powerwall 2+ units are charging at about 6 kW each every night at midnight. The rate is the same from then until 3 PM, so there is no reason to charge so fast. There really should be a setting for this, either in terms kW or time.

I even wonder if Tesla is asking for trouble with this approach. If thousands of customers charge at maximum rate at the exact same time, it is going to make the utilities want to do something about those load spikes. I'd rather self-regulate than be regulated.

There is something wrong with your system, probably in how your CTs are set up. Midnight to 15:00 is fifteen hours, at 6kW, would be 90kWh, which is way more power than two Powerwall 2+ units can hold.

 

[VeloSteve]

There is something wrong with your system, probably in how your CTs are set up. Midnight to 15:00 is fifteen hours, at 6kW, would be 90kWh, which is way more power than two Powerwall 2+ units can hold.

I was unclear. They charge at 6kW until full. That takes roughly 1 to 2 hours. I only mentioned the 15 hour available time to point out that they could charge at a much lower rate without any pricing issues. For example, if they charged at 2 kW each they would still be full by 6 AM.

 

[mw963]

I have no input on "why" your charging might have changed. As it pertains to this part, however, the feedback I have about grid charging at all is that Tesla has a different warranty on a tesla powerwall that is charged from the grid, vs one that is charged from solar.

The only reason that I can think of that would possibly be, is that there is some difference when charged from the grid. The only difference I can think of is sustained charge rate (as solar, over time, would scale up and down, while grid power, if on, would be a constant source.

If they are telling you it is because your grid code changed, perhaps tell them to change it to a grid code that charges at the rate you want?

Sorry, I've been very late replying to this. I made another effort to contact Tesla Europe and this time they told me that it was a change of policy and that the 3.7 kW charging rate has been superseded by the 5 kW rate, which corresponds with the max charging rate of Powerwall 2. The change in policy came exactly when I noticed it (ie late Feb 2023) and I suspect may well have been made when Octopus abandoned their Go Faster tariffs (five hours of off peak a night) and moved everyone to straight "Go" (four hours per night). Maybe they were worried that with only a four hour window of off peak some batteries might not have time to charge up fully (eg if it was very cold and the charging rate had to be held down for the initial charging window...)

 

[JohnRatsey]

Sorry, I've been very late replying to this. I made another effort to contact Tesla Europe and this time they told me that it was a change of policy and that the 3.7 kW charging rate has been superseded by the 5 kW rate, which corresponds with the max charging rate of Powerwall 2. The change in policy came exactly when I noticed it (ie late Feb 2023) and I suspect may well have been made when Octopus abandoned their Go Faster tariffs (five hours of off peak a night) and moved everyone to straight "Go" (four hours per night). Maybe they were worried that with only a four hour window of off peak some batteries might not have time to charge up fully (eg if it was very cold and the charging rate had to be held down for the initial charging window...)

I know from previous winters that the 3.7kW charging rate isn't quite enough to fully charge an empty Powerwall in 4 hours.

 

[xWren]

@mw963 my understanding is that Powerwalls in the UK were by default throttled to 3.7kW by a setting configured by the installer. This limit was to match the OffGen rules that allowed equipment that could output to the grid (solar panels and batteries) to be installed without additional inspection or load planning by the DSO. If you wanted to raise that to 5kW then you had to apply and pay, although in almost every situation the grid could handle it and it was paper exercise. I even had one potential installer offer to set it to 5kW anyway. Tesla at the time had the same limit apply to both charging and discharging even though the OffGen rule/permission only applied to export rate.

Maybe you are now on a version of firmware (from Feb 2023) that has separated the charging rate limit from the export limit. What version are you on? I am clearly still limited to charging at 3.7kW in time-based and down to 1.7kW in self-consumption,

Since Octopus fell out big time with Tesla I doubt if they are working in collusion in any way. The 5kW will not harm your battery, in fact charging of LiPo is specified at '1C', that is 14kW would be fine for the Powerwall. However it would be so useful for the owner to be able to control the rate, as I can with my (non-Tesla) car charger. My house is on a 60A transformer, I use my 4 hours of Octopus Go cheap energy to the full - charging the car, running the ASHP, dishwasher, washing machine and in low solar months charging the Powerwall, having none of these things happen too fast (and blow my mains) matters.

 

[BGbreeder]

@mw963 my understanding is that Powerwalls in the UK were by default throttled to 3.7kW by a setting configured by the installer. This limit was to match the OffGen rules that allowed equipment that could output to the grid (solar panels and batteries) to be installed without additional inspection or load planning by the DSO. If you wanted to raise that to 5kW then you had to apply and pay, although in almost every situation the grid could handle it and it was paper exercise. I even had one potential installer offer to set it to 5kW anyway. Tesla at the time had the same limit apply to both charging and discharging even though the OffGen rule/permission only applied to export rate.

Maybe you are now on a version of firmware (from Feb 2023) that has separated the charging rate limit from the export limit. What version are you on? I am clearly still limited to charging at 3.7kW in time-based and down to 1.7kW in self-consumption,

Since Octopus fell out big time with Tesla I doubt if they are working in collusion in any way. The 5kW will not harm your battery, in fact charging of LiPo is specified at '1C', that is 14kW would be fine for the Powerwall. However it would be so useful for the owner to be able to control the rate, as I can with my (non-Tesla) car charger. My house is on a 60A transformer, I use my 4 hours of Octopus Go cheap energy to the full - charging the car, running the ASHP, dishwasher, washing machine and in low solar months charging the Powerwall, having none of these things happen too fast (and blow my mains) matters.

Is that a 60A, three phase transformer? (Just curious..., e.g. 3x(60x240)?)

All the best,

BG

 

[xWren]

Is that a 60A, three phase transformer? (Just curious..., e.g. 3x(60x240)?)

Nope, single phase, and 60A seemed more than enough when installed. Now if they continue to incentivise small windows of cheaper electricity, then I do need to be able to manage the rate things consume grid power and/or time when they do that.

 

[BGbreeder]

Nope, single phase, and 60A seemed more than enough when installed. Now if they continue to incentivise small windows of cheaper electricity, then I do need to be able to manage the rate things consume grid power and/or time when they do that.

Gosh, that seems like a small needle to thread with an EV, air source heat pump, Powerwall, dishwasher, washing machine... It certainly highlights why the lower Powerwall charge rate would be an issue.

All the best,

BG

 

[xWren]

Gosh, that seems like a small needle to thread with an EV, air source heat pump, Powerwall, dishwasher, washing machine... It certainly highlights why the lower Powerwall charge rate would be an issue.

No aircon or heated pool.... our electricity use is very moderate compared to so many of the graphs I see on this forum. But lack of owner control of devices is an issue, the big corporation and the software they design does not know best and is not able to predict my use.

 

[mw963]

@mw963 my understanding is that Powerwalls in the UK were by default throttled to 3.7kW by a setting configured by the installer. This limit was to match the OffGen rules that allowed equipment that could output to the grid (solar panels and batteries) to be installed without additional inspection or load planning by the DSO. If you wanted to raise that to 5kW then you had to apply and pay, although in almost every situation the grid could handle it and it was paper exercise. I even had one potential installer offer to set it to 5kW anyway. Tesla at the time had the same limit apply to both charging and discharging even though the OffGen rule/permission only applied to export rate.

Maybe you are now on a version of firmware (from Feb 2023) that has separated the charging rate limit from the export limit. What version are you on? I am clearly still limited to charging at 3.7kW in time-based and down to 1.7kW in self-consumption,

Since Octopus fell out big time with Tesla I doubt if they are working in collusion in any way. The 5kW will not harm your battery, in fact charging of LiPo is specified at '1C', that is 14kW would be fine for the Powerwall. However it would be so useful for the owner to be able to control the rate, as I can with my (non-Tesla) car charger. My house is on a 60A transformer, I use my 4 hours of Octopus Go cheap energy to the full - charging the car, running the ASHP, dishwasher, washing machine and in low solar months charging the Powerwall, having none of these things happen too fast (and blow my mains) matters.

@ xWren - It says Version 23.44.0 eb113390. Is that what you were asking?

Interested to hear about the fall out between Tesla and Octopus. Is that why the Tesla Tariff disappeared?

 

[xWren]

Gosh, that seems like a small needle to thread with an EV, air source heat pump, Powerwall, dishwasher, washing machine... It certainly highlights why the lower Powerwall charge rate would be an issue.

@BGbreeder looking at my winter data (high use, low solar) my peaks in consumption are around 6kW, less than half the 14kW I have to play with. If Tesla would give me the control I can manage my resources really efficiently