We just had had a 17.5kW PV array with 2 inverters (7.0 and 7.7) installed plus 2 PowerWalls. In testing off-grid/self-powered mode, we are seeing issues with the PWs. With both inverters on (14.7 total) and peak sun, the PWs keep shutting the inverters off. Even with just one inverter on and PWs mostly charged, we sometimes see the whole house lose power (clocks reset/etc) for a several seconds – when this happens the Tesla app shows no power flowing between batteries and anything else. Any thoughts?
New PowerWall install woes
- Thread starter zƬesla
- Start date
Lloyd
Well-Known Member
I wonder if one of your Powerwalls is not working. With only one inverter going two Powerwalls should have no problem managing the solar power. However, if only one were accepting a charge, it's possible that the inverter is still overloading the Powerwall.
I think 14.7 kW is at the limit of what two Powerwalls can handle, but the fact that you're getting power outages with just one inverter running probably indicates something is wrong with the system.
I think 14.7 kW is at the limit of what two Powerwalls can handle, but the fact that you're getting power outages with just one inverter running probably indicates something is wrong with the system.
The Tesla guidance on maximum PV size per Powerwall is not great, IMO. Each PV configuration is different and there are a lot of factors to consider when planning Powerwall capacity (panel rating, inverter rating, actual peak, day and seasonal variations, etc) so a one-size-fits-all statement of "at least one Powerwall is required for each 7.6 kW AC of solar included in the backup circuit" allows for corner cases like this since the Powerwall is only rated for 5kW continuous power in or out. I get in to some detail on this point here Powerwall with non Tesla solar?
Since each Powerwall inverter can handle 5kW sustained you would need 4.7kw (14.7kw - 2x5kw each Powerwall) of house draw or PV shedding during peak production to charge safely. This is of course assuming your Powerwalls have some storage capacity available as they generally don't charge when over 95% and the grid is lost until they drop down under 95% (ish).
@zƬesla assuming you don't have a faulty Powerwall I think you have three options (copied from my post on that other thread
)1) Take advantage of your inverter's frequency power scaling. Many new PV inverters (and some old ones) are configurable to scale down production based on the grid frequency. SolarEdge inverters all it "P(F) Power Frequency" (https://www.solaredge.com/sites/default/files/application_note_power_control_configuration.pdf, page 6) and Enphase calls it "curtailment" or "ramp down" (https://enphase.com/sites/default/f...Considerations-AC-Coupling-Micros-Battery.pdf, page 6). Since the Powerwall will increase the power frequency during off grid operations to instruct the inverters how to behave you can match the Powerwall's frequency profile with your inverters to ensure that you never exceed the Powerwall limits. This is what I do for my 8.6kW PV system which just barely reaches the PV inverter rating of 6.6kW during the sunniest of days. If your system supports it this is probably the best way to go.
2) Shut off a PV inverter/string off during an outage. This is the least palatable option but one that some have floated on this board for large PV systems that aren't looking to add many Powerwalls. With this configuration you're essentially reducing the size of the PV system during an off grid operation keeping it under the Powerwalls' inverter limits. Open the breaker on one of your two inverters during the sunniest of days and close it back during cloudy days. More manual but keeps the Powerwalls from tripping and costs nothing.
3) Add a 3rd Powerwall. The 15kw max of 3x Powerwalls is well below your 14.7kw PV production. Of course this is a very pricy option.
Anecdotally I've seen the Powerwall take over a second to switch during an off grid test with peak sun when charged at 100%. My best guess is that this is to allow the PV to fully shut down first as a protective measure. Pure speculation on my part.
If 1 would have been an option, then we should not have been asked to switch one of the 7.7s to a 7.0 pre-install, thus losing peak PV, especially as the 7.7 inverter would not have cost us any more. Maybe they can upgrade to a v2 gateway next month as a way to partially make up for our revenue loss over the life of the system.
2 is really not really an option as I’m looking for an automated system. I can control house loads and tell guests how to (eg, don’t run dryer), but don’t want them (or me) to deal with turning inverters or PowerWalls on/off.
3 is a possible option if it can be done at cost. It’s not something we planned for financially at this time. And if the only real solution, makes me question Tesla’s certification of installers.
2 is really not really an option as I’m looking for an automated system. I can control house loads and tell guests how to (eg, don’t run dryer), but don’t want them (or me) to deal with turning inverters or PowerWalls on/off.
3 is a possible option if it can be done at cost. It’s not something we planned for financially at this time. And if the only real solution, makes me question Tesla’s certification of installers.
#1 - I wouldn't necessarily expect installers to know about these features, mine certainly didn't. SMA Sunny Boys calls this feature "Frequency-Watt Mode" https://files.sma.de/dl/27676/SBxx-1XP-US-40-GridServices-TI-en-15.pdf section 2.8 (page 15). Not sure what your inverter model is.
#2 - Yup, it's really a bummer for all of those reasons but again it's an option.
#3 - While this is a miss I wouldn't specifically put it on the installers. The Tesla guidance is not good (again, IMO) and technically the system is operating correctly given your setup. It's just not ideal.
If it were me I'd complain to the installer, ask them to get the Frequency-Watt Mode configured properly, and switch me back to the 7.7kw inverter. Not sure they'd do the latter given Tesla's guidelines but I'd personally take the shot
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I wonder whether the frequency watt mode will cause an issue with our UPSs. Also, what other side effects here may be.
On your last point, I would expect the installer to know the capabilities of their product up front and be able to advise on the proper sizing of the system. Otherwise, this might be seen as a way for them to rope someone into buying their services then afterwards forcing an upgrade for the system to function properly. In other words, I already paid them a premium for their expertise...
On your last point, I would expect the installer to know the capabilities of their product up front and be able to advise on the proper sizing of the system. Otherwise, this might be seen as a way for them to rope someone into buying their services then afterwards forcing an upgrade for the system to function properly. In other words, I already paid them a premium for their expertise...
It will not cause any issues or side effects if configured correctly. All this does is have your inverters produce less power depending on the local grid frequency, it does not affect anything your Powerwall does. For example I have my inverters configured to start ramp down at 60.20hz, ramp down to 0% at 61.40hz, and fully turn off at 61.80hz (rampdown and off are two different settings). My Powerwall is configured to set the frequency to 62.0hz maximum, well below my UPS' tolerances and well above the "off" points of the inverters. Since the Powerwall changes frequency slowly and lineally over time depending on battery charge level and PV production the PV will adjust accordingly to match. It's a bit of a balance game.
And yes, I completely totally agree that installers SHOULD know these things, I just don't EXPECT them to do given my experience and how new this tech is in the US
Like I said I'd bring it up and complain that this is a bad experience and get them to make it right.
GenSao
Member
Typically the whole house loses power during backup operations when there is too much load for the Powerwalls to handle. They will reset the power to the home hoping to force some loads to shed. This can happens when the AC kicks on and there is no soft/hard start device installed.
If this is not the case, then there is something weird going on that may not be attributed to being close to the recommended amount of solar per Powerwall (7.6 kW per Powerwall). First check in with your Tesla Certified installer on fixing the issue. They may have miss-configured your system, installed faulty hardware/wiring, or need to make minor adjustments for Gpez Option 1 to work. Second, Tesla may be able to remotely configure the Powerwall to coordinate solar production with your SMA inverters if your installer can not do it.
If Gpez Option 1 does not work, consider having your installer (at no additional cost to you) physically move the breakers for one of your inverters into the non-backup load panel for Gpez Option 2. In the event of grid outage, the solar inverter outside the backup gateway would automatically turn off. Not ideal, but works automatically to shed solar generation.
Ultimately your Tesla Certified installer needs to fix the system.
that’s where I’m at. Installers initial recommendations were to swap remaining 7.7 to 7.0, install a third battery, or install a device to cut off one inverter when PV was high. These were made before they even consulted Tesla, which they’re now finally doing.
There is no non-backup panel as it was apparently not called for.
There is no non-backup panel as it was apparently not called for.
Good point on moving one of the inverters to the other side of the gateway! While it makes production shedding automatic the drawback is you lose half of your PV production during an outage. If your home consumption is ~1kw on average then a 7.7kW is likely enough.
The main intent of the design was to extend outage power availability. Moving an inverter would defeat this. That’s also why we opted to drop the 7.7 to 7.0 at the installer’s advice instead of leaving out a string which would have lowered PV generation further.
The 1kw is not the average, rather the minimal load use with no extras on (eg, stove, dryer, ac)
The 1kw is not the average, rather the minimal load use with no extras on (eg, stove, dryer, ac)
Am I remembering correctly that in your situation, your PV installer and your Powerwall installer are different people / companies, AND both are new installations done within a couple of weeks of each other?
If so, the PV installer is / was not liable to configure the system for the powerwalls, and the powerwall installer technically doesnt have to do anything to configure the PV for ramping, etc... or thats what it would seem to me at least.....
In the above thread, this is sort of what I ment in the bolded part above. If the solar installer was not powerwall certified, they dont "have" to know all that much about number of powerwalls vs solar installation, etc. The powerwall installation company can always come back and say "well we installed what you bought, which is two powerwalls"....
hopefully this is something that can be worked out for OP to his favor.
PV installer provided diagram of system without batteries as they were engaged much earlier, before it was decided to get batteries. Tesla certified installer then provided PW diagram integrated with PV and their only ask was to step 7.7 inverter down to 7.0. Basically, PV design was changed based on Tesla installer recommendation of PW capabilities. I expected PW installer to know battery capabilities, especially as they asked for the inverter change. We’ll see where things end up; hoping for an amicable, quick, and fair solution.
Tesla guidance is "at least" one PW per 7.6KW AC so it seems the PW installer overlooked it and Tesla in not on the hook for the problem. The proper answer is really 3 PW's for the PV array size.
