Is Telsa proposing the right thing for my Powerwall installation?

[mongo]

Thank you for the info. For our back up system the only things we were planning on having on the single powerwall originally was the sump pump and our wireless router. Even with just these two items, there would still be too much inrush of electricity for a single powerwall. If we puchased a different sump pump, would this alleviate the demand on the powerwalk?

Yes, a 240 volt sump pump would pull half the current per phase. Grainger has them.

 

[Jay Roth]

Yes, a 240 volt sump pump would pull half the current per phase. Grainger has them.

Great, thank you for the information!

 

[Musterion]

If I'm really getting down to it, I don't even care that much about having backup power overnight. What I'm really trying to optimize for is automatic disconnect from the grid so I can use solar during the day of an outage. The entire situation feels like an extraordinary failure of product design.

I would say this is not the fault of product design but is just basics physics. When you are disconnected from the grid, you have to provide your own sink for all the energy you are generating, as you no longer have the luxury of an infinite reservoir provided by the electric company. In your case your storage capacity is undersized by nearly a factor of 2 compared to generation capability, so there is no other choice but to cap the solar production to match your available sink. As @Vines points out, if somehow you had a huge energy demand in the house beyond the battery, you could potentially turn on the excess solar, but for safety you would need this demand to be constant and guaranteed. People have speculated about building energy absorbers for this case, but in general that is a difficult practical project while it works in theory—most implementations would be dangerous given the amount of joule heating dissipated in a small volume. If you wanted to change the design of Powerwall, you couldn’t, for example, put such an absorber into the Powerwall itself without risking damage. Another design change might be for Powerwall to regulate total solar regulation, but there doesn’t exist a standard way to do this across all inverters, and that is not Tesla’s fault. So the best option currently is frequency-modulation and on-off control of inverters which is guaranteed to work across all inverters due to islanding regulations. (I had to consider similar issues in my own installation and learned a lot from the other threads on this and in particular the live data that @Ulmo has posted).

 

[Vines]

I would say this is not the fault of product design but is just basics physics. When you are disconnected from the grid, you have to provide your own sink for all the energy you are generating, as you no longer have the luxury of an infinite reservoir provided by the electric company. In your case your storage capacity is undersized by nearly a factor of 2 compared to generation capability, so there is no other choice but to cap the solar production to match your available sink. As @Vines points out, if somehow you had a huge energy demand in the house beyond the battery, you could potentially turn on the excess solar, but for safety you would need this demand to be constant and guaranteed. People have speculated about building energy absorbers for this case, but in general that is a difficult practical project while it works in theory—most implementations would be dangerous given the amount of joule heating dissipated in a small volume. If you wanted to change the design of Powerwall, you couldn’t, for example, put such an absorber into the Powerwall itself without risking damage. Another design change might be for Powerwall to regulate total solar regulation, but there doesn’t exist a standard way to do this across all inverters, and that is not Tesla’s fault. So the best option currently is frequency-modulation and on-off control of inverters which is guaranteed to work across all inverters due to islanding regulations. (I had to consider similar issues in my own installation and learned a lot from the other threads on this and in particular the live data that @Ulmo has posted).

This standard is in the works already, and its my understanding some inverters have this ability already. Within the next couple years I believe the Powerwall will be able to control the PV with more granular control over the PV output, rather than just off or on. All the components are in place, just need to get the firmware deployed.

 

[miimura]

I don't remember the details, but I thought that the new grid interactive requirements like rapid shutdown and reactive power first (or whatever it's called) were technically at odds with proper micro-grid frequency-proportional curtailment. I thought I heard about a solar inverter that could do the proportional curtailment in the settings, but you could not enable those settings and still meet all the new requirements for California & Hawaii grid interconnection.

 

[mspohr]

The new standard for grid support functions is UL 1741

http://www.outbackpower.com/downloa...2017_SA_Grid_Supporting_Functions_summary.pdf

 

[Vines]

UL 1741 has been in place for a while, about 10 years, the new version is 1741 SA.

I expect that the standards can come to a place where partial curtailment is possible. I know its being worked on and as soon as the bureaucracy catches up this will be possible I hope.

 

[miimura]

I would be nice if there was a standard way to signal AC coupled solar inverters that they were off-grid so they could go into a different operating mode that would help the stability of the micro-grid.

 

[mongo]

I would be nice if there was a standard way to signal AC coupled solar inverters that they were off-grid so they could go into a different operating mode that would help the stability of the micro-grid.

What kind of mode change are you thing of?
Enphase and such vary their output based on voltage and/or frequency. Beyond that, the only other factor that would help is the rate at which they change their output (sudden load handling). Inverters may rely on the grid not caring about their response time and thus take things slowly. However, a fast response system would work as well on grid as off.
I am wondering if an AC motor with a large flywheel would help with regulation (although you might need 3 phase power).

 

[Vines]

The old version of 1741 allowed up to (I think) 60.5 Hz frequency. The new version (Rule 21 SA) allows up to 62 Hz for 5 minutes, they call this ride through. Imagine if the frequency shifting driven by the battery inverter beyond that from 60.5-62 lowered the PV inverters output. So the battery inverter could frequency shift to the required frequency for less than 5 minutes (to prevent total inverter disconnection as required by 1741 SA, and the PV inverter would recognize this as a signal to curtail production for the next 10 minutes, or until it recognizes the restoration of Near Nominal frequency.

60.5 = 80% output
61 = 60% output
61.5 = 40% output
62 = 20% output
Beyond = 0% (inverter off)

See sheet 15 of the following doc. https://aeesolar.com/wp-content/uploads/2017/08/UL-1741-Supplement-A_Webinar.pdf
This details how the inverter will respond to frequency and curtail or increase power output.

 

[miimura]

What kind of mode change are you thing of?
Enphase and such vary their output based on voltage and/or frequency. Beyond that, the only other factor that would help is the rate at which they change their output (sudden load handling). Inverters may rely on the grid not caring about their response time and thus take things slowly. However, a fast response system would work as well on grid as off.
I am wondering if an AC motor with a large flywheel would help with regulation (although you might need 3 phase power).

I have old Enphase micros from 2012 and my Powerwalls are tending to get stuck at 63Hz when the grid is down and the batteries are between 20% and 80%. These old solar inverters tend to be on or off. It does seem that the new IQ7 series have ride through that might be more interoperable with the Powerwall. However, I feel the Powerwall software still has a bug in the frequency control.

 

[Vines]

I have old Enphase micros from 2012 and my Powerwalls are tending to get stuck at 63Hz when the grid is down and the batteries are between 20% and 80%. These old solar inverters tend to be on or off. It does seem that the new IQ7 series have ride through that might be more interoperable with the Powerwall. However, I feel the Powerwall software still has a bug in the frequency control.

Strange behavior there. Are you saying that below 20% SoC it will charge batteries, then stop at 20% SoC? Are you on the latest firmware?

 

[miimura]

Strange behavior there. Are you saying that below 20% SoC it will charge batteries, then stop at 20% SoC? Are you on the latest firmware?

No, my main point is that while the Powerwalls are in the middle of the SOC range (20% - 80%) they should operate with the solar completely autonomously while the grid is down. Instead, it is pushing the frequency to 63Hz which shuts off my solar. This is very bad during an extended outage like what @MorrisonHiker recently experienced. I have a way to extend the runtime of my Powerwalls, but it should not be necessary to resort to that if I can manage my loads within my daily solar generation. I am on 1.32.0. I last experienced this problem during an outage in November. I will probably trigger a test outage this weekend by flipping my main breaker to see if it still happens. As you can see from my sig, it should be impossible for my solar to overpower my Powerwalls.

 

[shs1]

No, my main point is that while the Powerwalls are in the middle of the SOC range (20% - 80%) they should operate with the solar completely autonomously while the grid is down. Instead, it is pushing the frequency to 63Hz which shuts off my solar. This is very bad during an extended outage like what @MorrisonHiker recently experienced. I have a way to extend the runtime of my Powerwalls, but it should not be necessary to resort to that if I can manage my loads within my daily solar generation. I am on 1.32.0. I last experienced this problem during an outage in November. I will probably trigger a test outage this weekend by flipping my main breaker to see if it still happens. As you can see from my sig, it should be impossible for my solar to overpower my Powerwalls.

As you know, I have had exactly the same issue with the PW2 shutting down my solar be raising the frequency to 66 Hz even when my SOC is less than 50% and the solar panels/inverters are putting out less than 3 kW which my PW2 should be able to take. My installer is working with Tesla to resolve this (I hope). I am on 1.34.2 and it is likely time for another test power failure. I just hate having the appliances, lights and UPSs in my house have to deal with that out of normal range frequency. Is this not a problem?

 

[MorrisonHiker]

As you know, I have had exactly the same issue with the PW2 shutting down my solar be raising the frequency to 66 Hz even when my SOC is less than 50% and the solar panels/inverters are putting out less than 3 kW which my PW2 should be able to take. My installer is working with Tesla to resolve this (I hope). I am on 1.34.2 and it is likely time for another test power failure. I just hate having the appliances, lights and UPSs in my house have to deal with that out of normal range frequency. Is this not a problem?

We did notice during our outage when the Powerwalls were powering the house that the clocks all ran fast and the induction range didn't work.

 

[shs1]

Yes it is very convenient to have the PW2 powering the house during a power failure, but if your refrigerator, freezer, induction cooktop, other appliances and lights are not working, it sort of defeats the point!

 

[mspohr]

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