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Optimizing Powerwall for Grid Export Limited Systems

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Hi Folks,

New poster here. I was hoping someone might be able to help me with my Powerwall conundrum. It arises because of the 5kW grid export limit imposed by the utility in my area.

The current behavior of the Powerwall is to begin charging in the morning as soon as solar generation > home usage. Once the Powerwall is fully charged (usually before 11am on a sunny summer day) it will switch to grid exports.

By the late morning, the Powerwall is fully charged, and I’m generating over 5kW, which is when my inverter starts throttling back the solar output. I end up with a generation curve with the top ‘chopped off’:
Current Behaviour.PNG


I estimate I’m missing out on nearly 10kWh per day over the middle of summer because of this.


Here's how I would like the Powerwall to behave:
Before 11am, just export to the grid. Don't charge at all.
From 11am - 3pm, charge the battery (but at a capped rate, say 2-3kW)
After 3pm, if the battery isn't already full, charge at an uncapped rate.

My generation graph from before would hopefully look more like this:
Desired Behaviour.PNG


Any ideas on how I might achieve this?

I've played around with the advanced time-based mode; effectively trying to 'trick' the system into only charging during off-peak times. Haven't had any success so far though.
 
You can’t make what you want happen.

the only time I’ve seen what you’re experiencing, is when the PTO hasn’t been granted or the inverters got an odd bit of software through update or glitching. This stopped happening on our system with 1.46.0
Restarting them helps sometimes, follow proper guide to your system for full shutdown and boot up.
 
You can’t make what you want happen.

the only time I’ve seen what you’re experiencing, is when the PTO hasn’t been granted or the inverters got an odd bit of software through update or glitching. This stopped happening on our system with 1.46.0
Restarting them helps sometimes, follow proper guide to your system for full shutdown and boot up.
Thanks for the reply.

Unfortunately, the inverter is doing exactly what it's programmed to do and I can't change it. It's set in the factory to limit all grid exports to 5kW (As mandated by the local utility).

I'm hoping to time-shift the powerwall charging to the middle of the day so I can maximize grid exports and feed-in tariff earnings.
 
Thanks for the reply.

Unfortunately, the inverter is doing exactly what it's programmed to do and I can't change it. It's set in the factory to limit all grid exports to 5kW (As mandated by the local utility).

I'm hoping to time-shift the powerwall charging to the middle of the day so I can maximize grid exports and feed-in tariff earnings.

that’s a bummer about the utility co.

the only way I could see that you’ll be able to “time shift” as you say, in the current config:
Is don’t drain them overnight OR manually flip the powerwall power switches. Every. Single. Day.
 
I've played around with the advanced time-based mode; effectively trying to 'trick' the system into only charging during off-peak times. Haven't had any success so far though.

I am in a jurisdiction that doesn't have these limits or TOU pricing, so I haven't had reason to use the time-based controls beyond a brief look at it, but what settings were you using? I might have thought that setting 11am-3pm as off peak, 3-8pm (~sunset) as shoulder, and the rest as peak might work, along with a low (possibly 10%) reserve setting, and I think cost-saving mode. The idea would be that at 11am, the powerwalls would be at the reserve, and then would charge 11-3 (though unfortunately not at a capped rate.) If they are not yet charged, they could continue charging during the shoulder period. Then, Tesla is supposed to learn your energy patterns and begin discharging during peak and possibly shoulder to get you back to 10% by 11am the next day. Since it is supposed to be "learning", it might take some time to get things working better since this is an odd set of conditions (and maybe it is odd enough it just won't work.)

It would be great if Tesla added more options to the advanced mode for these types of situations, but it seems like the time-based controls might have a chance to at least capture some of the generation you are missing out on.
 
that’s a bummer about the utility co.

Yeah it sucks but they had to do it. So many people are getting solar in my state, they were losing control of the grid.

I might have thought that setting 11am-3pm as off peak, 3-8pm (~sunset) as shoulder, and the rest as peak might work, along with a low (possibly 10%) reserve setting, and I think cost-saving mode. The idea would be that at 11am, the powerwalls would be at the reserve, and then would charge 11-3 (though unfortunately not at a capped rate.) If they are not yet charged, they could continue charging during the shoulder period. Then, Tesla is supposed to learn your energy patterns and begin discharging during peak and possibly shoulder to get you back to 10% by 11am the next day. Since it is supposed to be "learning", it might take some time to get things working

Thanks for the suggestion. I'll have a try. Problem is because it tries to 'learn', you really have to leave it with the same configuration for 2 weeks or so to see if it's working. Makes it a nightmare to test different settings.

since this is an odd set of conditions (and maybe it is odd enough it just won't work.)

Yeah I appreciate this is a fringe case at the moment. I can see it becoming a more common problem though as grids around the world start seeing more and more behind-the-meter solar.
 
Thanks for the suggestion. I'll have a try. Problem is because it tries to 'learn', you really have to leave it with the same configuration for 2 weeks or so to see if it's working. Makes it a nightmare to test different settings.
In my experience most of this learning is sort of fringe stuff. IE when it gets near a different TOU structure (Ths and Fri when a weekend has different structure) it will mess with the soc. Otherwise mine seems to try to charge to 100% like you described and then bleed it off during peak. It certainly knows nothing about weather, and that has a huge impact on production.

Any I would think you could lie to it about your rates in Time Based Control and have it avoid those periods. Perhaps tell it that your max rate is in the mid morning. It will certainly take some experimenting.

The other option is to use the API to control what it is doing but that is a whole other subject and fairly complex plus you would need the infrastructure and the algorithms.
 
Yeah I appreciate this is a fringe case at the moment. I can see it becoming a more common problem though as grids around the world start seeing more and more behind-the-meter solar.

Definitely, and in general, there are a lot of different fringe cases that perhaps could be supported by a manual mode that could let you program precise rules for your circumstances (and bypass the learning algorithms.) I know there is a SmartThings app that was created (and there is a post about it somewhere on these forums) but I don't think even that has the option you really are looking for to split the extra supply between grid and powerwall.
 
In my experience most of this learning is sort of fringe stuff.

Fair enough. The 'let it learn for two weeks' thing is what a Tesla support guy told me when I tried to explain this issue to him over the phone.

The other option is to use the API to control what it is doing but that is a whole other subject and fairly complex plus you would need the infrastructure and the algorithms.

Not really a rabbit hole I wanted to go down but might be my only option.

I just wish there was some sort of 'expert' mode in the app, so you could customize things a bit more.