SRP demand (kW) number is huge different with Powerwall app

[SuperCarrot]

I'm a new Powerwall user in Phoenix, AZ. I just started using SRP's Time-of-Use Demand Plan (this is E-27 plan, not the average Demand plan E-15). This plan will charge regarding on-peak time demand (kW) which is measured in 30-minute interval. For example, in 7pm-7:30pm, if 10 minutes grid power demand is 3 kW, the other 20 minutes grid power demand is 0 kW, then demand for this 30-minute interval is 1 kW. SRP will charge by the number of demand. Yesterday is my first day to use this plan, I found the demand measured by SRP is huge different with Powerwall app.

The first chart below is SRP Demand data, it shows the demand on 7:30pm-8:00pm is 2.6 kW. The second chart is SRP Usage data, it shows usage between 7pm-8pm is 1.5kWh. Red bar means on-peak time.

But Powerwall data (both graphic and downloaded spreadsheet) show grid demand in this time period is 0. All demand is loaded on Powerwall battery rather than grid. The screenshot below is from Powerwall app downloaded spreadsheet. The highlighted rows are time period 7:30pm-8:00pm (please ignore the '-07:00' at the end of each time, I don't know what's that mean). This spreadsheet shows in this period demand is all on Powerwall, grid demand is always 0. It's super weird SRP data is 2.6 kW. SRP will charge me on this demand number, and demand charge is quite expensive.

The same situation also happened on 7:00am-7:30am. SRP data shows demand is 1.2 kW, but Powerwall app shows 0 demand on grid.

In the on-peak time yesterday, I set Powerwall Self-Powered mode (Back up reserve was set 10%). So I don't think it used power from grid, since Powerwall has enough power at that moment. I don't know where the problem is (Tesla side or SRP side). This situation makes me have no confidence at all to use Powerwall in on-peak time. Does anyone have similar experience? Any thought is welcome. Appreciate it.
I have one Powerwall+ with firmware version 21.44, app version is 4.3.1 on Android. By the way, I got "Go Off-Grid" button showing up in the app today, I tried to enable the off-grid mode, it doesn't work properly. Once click that button, the power is cut off for one or two seconds, then grid is connected back. Powerwall never works on off-grid mode. There's just around 0.3 kW load at the moment when I tried it, so it should have nothing to do with the load. I'm not sure if this is related with the demand measuring issue I talked above.

 

[slcasner]

The highlighted rows are time period 7:30pm-8:00pm (please ignore the '-07:00' at the end of each time, I don't know what's that mean).

The '-7:00' indicates the time zone of the timestamp. In this case your time zone is Mountain Standard Time which is 7 hours west of the Greenwich meridian (7 hours less that GMT/UTC time).

 

[SuperCarrot]

The '-7:00' indicates the time zone of the timestamp. In this case your time zone is Mountain Standard Time which is 7 hours west of the Greenwich meridian (7 hours less that GMT/UTC time).

Thank you, it's good to know.

 

[slcasner]

I agree that this data seems inconsistent. SRP can't see what is happening behind the utility meter, so it must be the case that power is being drawn through that meter. My first thought was that the CTs that the Powerwall system uses to measure where power is going within the system might be installed incorrectly such that power indicated as coming from the battery was actually coming from the grid. But the Energy Remaining (%) column indicates that the battery is discharging. I also considered whether the batteries might be charging from the grid, but then the numbers in the Powerwall column should be negative. I don't have any ready explanation.

 

[power.saver]

I agree that this data seems inconsistent. SRP can't see what is happening behind the utility meter, so it must be the case that power is being drawn through that meter. My first thought was that the CTs that the Powerwall system uses to measure where power is going within the system might be installed incorrectly such that power indicated as coming from the battery was actually coming from the grid. But the Energy Remaining (%) column indicates that the battery is discharging. I also considered whether the batteries might be charging from the grid, but then the numbers in the Powerwall column should be negative. I don't have any ready explanation.

The powerwall doesn't respond instantly to changes in demand. If a heavy load is turned on, there can be a brief draw from the grid.

 

[slcasner]

The powerwall doesn't respond instantly to changes in demand. If a heavy load is turned on, there can be a brief draw from the grid.

Yes, but the OP says that the SRP peak demand is a 30-minute average. Maybe a huge load that was switching on and off rapidly could do this?

 

[power.saver]

Yes, but the OP says that the SRP peak demand is a 30-minute average. Maybe a huge load that was switching on and off rapidly could do this?

OP is wrong about E-27 demand charges. It is not an average over 30 minutes, but the highest instantaneous demand in a 30-minute interval.

 

[SuperCarrot]

OP is wrong about E-27 demand charges. It is not an average over 30 minutes, but the highest instantaneous demand in a 30-minute interval.

My understanding for SRP E-27 demand calculation should be correct. Before I started the plan, I have confirmed with SRP that E-27 every demand is measured as the average of every 30 minutes. SRP will charge regarding the largest number in this billing cycle.

 

[SuperCarrot]

OP is wrong about E-27 demand charges. It is not an average over 30 minutes, but the highest instantaneous demand in a 30-minute interval.

Even if regardless how demand was calculated, I still have question how the 1.5 kWh grid usage came from between 7pm-8pm. The usage number should be large enough for Powerwall app having something on track. But Powerwall spreadsheet data shows nothing from grid in this period.

 

[SuperCarrot]

I agree that this data seems inconsistent. SRP can't see what is happening behind the utility meter, so it must be the case that power is being drawn through that meter. My first thought was that the CTs that the Powerwall system uses to measure where power is going within the system might be installed incorrectly such that power indicated as coming from the battery was actually coming from the grid. But the Energy Remaining (%) column indicates that the battery is discharging. I also considered whether the batteries might be charging from the grid, but then the numbers in the Powerwall column should be negative. I don't have any ready explanation.

Yeah, it's a reasonable doubt that something was not installed correctly. From the data I have so far, it looks all the battery load was counted as grid load. Should this be Tesla installation issue or SRP meter installation issue?

 

[ptdusn]

Yeah, it's a reasonable doubt that something was not installed correctly. From the data I have so far, it looks all the battery load was counted as grid load. Should this be Tesla installation issue or SRP meter installation issue?

This would be a Tesla issue. I too am with SRP in Phoenix area and I am on the E-13 plan as there are NO demand charges. I also am having a data issue where the house power indication jumps up when there is grid draw, but the when running off solar or the batteries it reads normally.

 

[SuperCarrot]

This would be a Tesla issue. I too am with SRP in Phoenix area and I am on the E-13 plan as there are NO demand charges. I also am having a data issue where the house power indication jumps up when there is grid draw, but the when running off solar or the batteries it reads normally.

Did you contact Tesla? Did they give any diagnosis result or solution?

 

[ptdusn]

I have my installer, SunRun coming out to troubleshoot system. Being an Electronics Tech i presented them with a mountain of evidence via screenshots when Storm Watch was activated.
I would highly recommend switching to the E-13 plan as you may get wacked from the demand charges in summer.

 

[SuperCarrot]

I have my installer, SunRun coming out to troubleshoot system. Being an Electronics Tech i presented them with a mountain of evidence via screenshots when Storm Watch was activated.
I would highly recommend switching to the E-13 plan as you may get wacked from the demand charges in summer.

Glad to hear your issue is taken care. I was initially on E-13 plan, I thought E-27 maybe more economy, so just switched to E-27 couple days ago.

 

[ptdusn]

Glad to hear your issue is taken care. I was initially on E-13 plan, I thought E-27 maybe more economy, so just switched to E-27 couple days ago.

Unfortunately, you won't be able to switch back for a year. I think you will be paying more on E-27

 

[slcasner]

Yeah, it's a reasonable doubt that something was not installed correctly. From the data I have so far, it looks all the battery load was counted as grid load. Should this be Tesla installation issue or SRP meter installation issue?

The SRP meter sits between the incoming service line and everything else. There is no place for an installation issue (well, there was a post in this forum about a badly installed meter socket that shorted across one leg of the meter so it undercounted the power consumed, but that would be very rare). Utility meters are also typically tested and calibrated before installation. But if the SRP billing did depend upon the instantaneous maximum power draw, that could be an issue.

 

[SuperCarrot]

The SRP meter sits between the incoming service line and everything else. There is no place for an installation issue (well, there was a post in this forum about a badly installed meter socket that shorted across one leg of the meter so it undercounted the power consumed, but that would be very rare). Utility meters are also typically tested and calibrated before installation. But if the SRP billing did depend upon the instantaneous maximum power draw, that could be an issue.

No, it doesn't depend upon instantaneous maximum demand. It depends upon 30-minutes average. This is confirmed by SRP.

 

[SuperCarrot]

I found something crazy. My extra solar power exported back SRP was not credited, but counted as my grid demand. Take 12/17 data as example, I was out of town entire day this day, I set Powerwall self-powered. The Powerwall data indicates almost all power consumed was from battery and solar, and the extra solar generated power was exported back to SRP between 1pm ~ 5pm. But look at the SRP data, it counted all battery usage/demand as grid usage/demand, and counted export kW as grid demand! IT IS CRAZY!

SRP demand/usage data

Powerwall data

 

[slcasner]

I found something crazy. My extra solar power exported back SRP was not credited, but counted as my grid demand. Take 12/17 data as example, I was out of town entire day this day, I set Powerwall self-powered. The Powerwall data indicates almost all power consumed was from battery and solar, and the extra solar generated power was exported back to SRP between 1pm ~ 5pm. But look at the SRP data, it counted all battery usage/demand as grid usage/demand, and counted export kW as grid demand! IT IS CRAZY!

Aha! Some utility meters that are not capable of Net Metering will behave that way -- energy flowing in either direction is treated as energy consumed.

 

[SuperCarrot]

Aha! Some utility meters that are not capable of Net Metering will behave that way -- energy flowing in either direction is treated as energy consumed.

Does that mean the issue is on SRP meter? Can this explain the issue I'm having on usage/demand read? SRP meter is supposed to support net metering, because SRP has E15 and E27 plans that need net metering.
I'm also thinking of if this is related with my "go off-grid" malfunction issue that I mentioned at end of the post.