Discussion: Powerwall 3 [Speculation / Discussion etc]

[mongo]

I received my first selling event with my 4 x PW3. 150 amp service. It seems like my powerwall discharging (combined) caps at a rate of 17-18 kW.

Specs show a max discharge rate of 11.5 kW each, shouldn't it be capable of discharging faster? Or am I limited by my 150 amp service?

View attachment 1029685

Does the power company agreement cap maximum export? I know some places treat >20kW differently for instance.

 

[SteveO332]

Does the power company agreement cap maximum export? I know some places treat >20kW differently for instance.

Here's the agreement. Cap is 42?

 

[mongo]

Here's the agreement. Cap is 42?

View attachment 1029691

May be a software limit for battery vs solar sourced power then.
150A service itself is only 36kW, do you really have that much solar?

 

[SteveO332]

May be a software limit for battery vs solar sourced power then.
150A service itself is only 36kW, do you really have that much solar?

I have a 23.49kw system.

Claude seems to think that it's a limiting factor.

Yes, it's quite possible that your 150 amp service is limiting the combined discharge rate of your Powerwall 3 units. Here's why:

A 150 amp service at 240 volts can theoretically provide a maximum power of 36 kW (150A × 240V = 36,000W or 36 kW). However, the National Electrical Code (NEC) requires that the total load on a service panel not exceed 80% of its rated capacity for continuous loads. This means that your 150 amp service can safely handle a continuous load of up to 28.8 kW (36 kW × 0.8 = 28.8 kW).

If each Powerwall 3 has a max discharge rate of 11.5 kW, then four units could potentially deliver a combined 46 kW (11.5 kW × 4 = 46 kW). This exceeds the safe continuous load capacity of your 150 amp service.

The 18 kW total discharge rate you're observing might be a result of the system limiting the output to prevent overloading your 150 amp service. Upgrading to a 200 amp service would provide a higher capacity:

200A × 240V = 48 kW
48 kW × 0.8 = 38.4 kW (safe continuous load for 200A service)

With a 200 amp service, your electrical system would be able to safely handle the combined maximum discharge rate of your four Powerwall 3 units (up to 46 kW), allowing you to take full advantage of their power output capabilities.

 

[Vines]

I have a 23.49kw system.

Claude seems to think that it's a limiting factor.

I was going to ask the same question when you mentioned "Sell Event"

A pure south 23.49 kW DC STC system at this time of the year would produce about 18 kW. Maximum performance depends on which direction your array faces, and whether the roof surfaces are mixed orientations and how close to 26 degrees your roof slope is.

If you have a perfect south roof tilted at 26 degrees you will probably see a maximum of about 21-22 kW from that size of system.

 

[SteveO332]

I was going to ask the same question when you mentioned "Sell Event"

A pure south 23.49 kW DC STC system at this time of the year would produce about 18 kW. Maximum performance depends on which direction your array faces, and whether the roof surfaces are mixed orientations and how close to 26 degrees your roof slope is.

If you have a perfect south roof tilted at 26 degrees you will probably see a maximum of about 22 kW from that size of system.

Understood, but that wouldn't affect the powerwalls ability to discharge, right?

I'm a Tesla Electric customer, so I had just assumed when sell prices spiked above $0.30 like in that screenshot, it would discharge at max rate, which is technically much higher than the 18kw it was showing in the app.

(if my understanding is accurate that the max discharge is 11.5 x 4 = 46 kw)

 

[Vines]

Understood, but that wouldn't affect the powerwalls ability to discharge, right?

I'm a Tesla Electric customer, so I had just assumed when sell prices spiked above $0.30 like in that screenshot, it would discharge at max rate, which is technically much higher than the 18kw it was showing in the app.

I didn't see the screenshot you mentioned and am not sure how a battery in Texas is programmed to discharge.

 

[mongo]

Understood, but that wouldn't affect the powerwalls ability to discharge, right?

I'm a Tesla Electric customer, so I had just assumed when sell prices spiked above $0.30 like in that screenshot, it would discharge at max rate, which is technically much higher than the 18kw it was showing in the app.

(if my understanding is accurate that the max discharge is 11.5 x 4 = 46 kw)

Oh, in that case the discharge rate may have been set by Tesla dynamically.

I was going to ask the same question when you mentioned "Sell Event"

A pure south 23.49 kW DC STC system at this time of the year would produce about 18 kW. Maximum performance depends on which direction your array faces, and whether the roof surfaces are mixed orientations and how close to 26 degrees your roof slope is.

If you have a perfect south roof tilted at 26 degrees you will probably see a maximum of about 21-22 kW from that size of system.

This was a night event, no solar.

 

[Vines]

This was a night event, no solar.

EDIT I see it now, but still don't understand the sell price.

From the installation side, there may be a PCS control limit set, or as mentioned above that Tesla maybe controlling this.

 

[SteveO332]

Oh, in that case the discharge rate may have been set by Tesla dynamically.

Ah! Ok, I didn't realize Tesla would control the discharge rate in that case. Makes sense now.

Sorry if I'm confusing folks on the sell event thing. Tesla Electric lets me sell back in real-time prices, and this was just one occasion where it spiked above $0.30, which triggered the powerwalls to discharge.

 

[SteveO332]

From the installation side, there may be a PCS control limit set, or as mentioned above that Tesla maybe controlling this.

I did get a chance to log via the Tesla One app, but didn't see any limits there. In PCS Settings, I see 80A panel limit and nothing specific that catches my eye in the import & export controls.

 

[Vines]

I did get a chance to log via the Tesla One app, but didn't see any limits there. In PCS Settings, I see 80A panel limit and nothing specific that catches my eye in the import & export controls.

View attachment 1029713

So your system is still set with the default 80A setting for Backup Switch jobs. This means that your system will throttle itself at 80A which works out to 19.2 kW, if PV measurement is accurate. I the limit in your case should be 120A which is 80% of the 150A service.

However there maybe reasons why they set it here that I don't know.

 

[Vines]

So your system is still set with the default 80A setting for Backup Switch jobs. This means that your system will throttle itself at 80A which works out to 19.2 kW, if PV measurement is accurate. I the limit in your case should be 120A which is 80% of the 150A service.

However there maybe reasons why they set it here that I don't know.

Also, Panel Limits will reduce Battery discharge at 90% of the rating. So the battery will stop discharging at about 17.3 kW, when panel limits are set to 80A.

 

[SteveO332]

Also, Panel Limits will reduce Battery discharge at 90% of the rating. So the battery will stop discharging at about 17.3 kW, when panel limits are set to 80A.

You're awesome, thank you for this guidance. I am speaking with Tesla Powerwall support now, and they said it is, in fact, wrong. My plan set says it supposed to be 200 amps.

They put in a ticket and will update it, has to go to a higher tier to update that settings. 3-5 business days.

 

[Vines]

You're awesome, thank you for this guidance. I am speaking with Tesla Powerwall support now, and they said it is, in fact, wrong. My plan set says it supposed to be 200 amps.

They put in a ticket and will update it, has to go to a higher tier to update that settings. 3-5 business days.

View attachment 1029723

Not sure about your Service panel design, but if you have a 150A service the limit should typically be 80% of the main breaker rating. Does your 150A service also have a 150A busbar?

200A is the maximum setting for panel limits but I don't think you want to set it there as then your batteries could backfeed 180A into the grid continuously.

 

[SteveO332]

Not sure about your Service panel design, but if you have a 150A service the limit should typically be 80% of the main breaker rating. Does your 150A service also have a 150A busbar?

200A is the maximum setting for panel limits but I don't think you want to set it there as then your batteries could backfeed 180A into the grid continuously.

I think I'm wrong on the 150 service amps...I looked at my main breaker and it has 150 on it, but the plan set has something different.

Does this plan set show that it's actually a 200 service? Apologies in advance for the dumb question.

 

[Vines]

I think I'm wrong on the 150 service amps...I looked at my main breaker and it has 150 on it, but the plan set has something different.

Does this plan set show that it's actually a 200 service? Apologies in advance for the dumb question.

View attachment 1029724

No, your plan set shows a 150A service. My advice stands, but your installer may know more than I do since they were there.

 

[SteveO332]

No, your plan set shows a 150A service. My advice stands, but your installer may know more than I do since they were there.

Got it, thanks again. Tesla Powerwall support did mention that they may not want to go all the way to 200, but would let me know what setting they adjust to after reviewing. I'll report back when I hear back.

 

[Vines]

Got it, thanks again. Tesla Powerwall support did mention that they may not want to go all the way to 200, but would let me know what setting they adjust to after reviewing. I'll report back when I hear back.

My understanding is that Panel Limits should be set at the 80% rating of the main breaker. However the 2020 NEC code isn't amazing with regard to PCS rules so an argument might be made for 100% of the breaker rating. I choose to be conservative until I know more.

 

[mongo]

My understanding is that Panel Limits should be set at the 80% rating of the main breaker. However the 2020 NEC code isn't amazing with regard to PCS rules so an argument might be made for 100% of the breaker rating. I choose to be conservative until I know more.

Since the limit is for battery not solar, would the 90% stack on the 80%, in which case to get 80% you need 150*.8/.9=133A? Where 133A*90%=120A=150A*80A