Running Solar with one Powerwall 2: Individual Backup Battery Issue/Question

[FGC92]

Well.. I am glad I found this post.
I just got a new solar panel system installed (14.3Kw) with one PW2.
I was doing a proof of concept a couple of days ago to my neighbors. The PW2 was charged at 100%, the house was using about 1.3Kw, the panels were generating about 11Kw, 9.7Kw was sent back to the grid.

I shut down the main, and BOOM. All LEDs in the house start flickering (everything is LED). My USP backups start beeping, and the LEDs that were off can't be turned on. I had to turn all lights off obviously. But this is a disaster.

This is what I figured out in this scenario.
When the PW2 is fully charged, it will send 65.9Hz frequency to the house (and the inverters, so they can shut down).
The PW2 will discharge until it reaches 90%. At this point, the frequency goes down to 60Hz, everything works fine.
The inverters will restart, and the battery will charge again. But I have an issue here because I generate 11Kw, the battery can only take 5Kw intake, and my house is using 1.3Kw
Once the PW2 reaches 98%, we are going back into flickering mode.

So I plan to switch back my lights in the house to regular bulbs.
I wish Tesla explained this to me at the time. I'd never have sign up to have PW installed I think.

 

[Dan123]

Well.. I am glad I found this post.
I just got a new solar panel system installed (14.3Kw) with one PW2.
I was doing a proof of concept a couple of days ago to my neighbors. The PW2 was charged at 100%, the house was using about 1.3Kw, the panels were generating about 11Kw, 9.7Kw was sent back to the grid.

Can you set your PW2 to not charge more than 80%?

 

[Vines]

The issue is that the Powerwall tells the PV system that it is done charging by shifting the grid frequency.

Regardless what level you tell the battery to stop at, when it does sense its full, it will turn off the PV by shifting frequency.

Generally its a bad idea to design these systems with more than 5-7 kw of PV generation for each Powerwall. One potential work around is to manually disconnect some of your PV breakers when the power goes out. Also, if you wanted a long term solution and you didn't have a whole home backup system, you might split some of the pv to the non backed up side. This way you still get the same backfeed, just reduced solar generation when the grid goes down.

 

[abasile]

When the PW2 is fully charged, it will send 65.9Hz frequency to the house (and the inverters, so they can shut down).

This has been discussed elsewhere, but part of the problem is that some "non compliant" solar inverters won't shut down until the frequency gets close to 66 Hz, so the Powerwall is outputting at that high frequency to be on the safe side, to be absolutely sure that the solar isn't back feeding into the grid. I suspect you'd have fewer issues at 63 Hz, and Tesla could in theory limit the frequency to 63 Hz if they could be assured that your inverters are compliant. We've had no real issues with LED lights at 63 Hz, though our induction stove and UPSs don't like it.

Can you set your PW2 to not charge more than 80%?

A "maximum charge" setting is something I've requested from Tesla, partly to leave headroom for charging during outages, but they haven't implemented it. In the Advanced (TOU) modes, setting the backup reserve percentage to a lower value might help to limit the charge, but there's no guarantee, and the charge behavior has varied quite a bit with successive Powerwall software releases. However, if the solar inverters are outputting more power than the maximum charge rate of the Powerwall(s), then they have to be shut down regardless.

Generally its a bad idea to design these systems with more than 5-7 kw of PV generation for each Powerwall. One potential work around is to manually disconnect some of your PV breakers when the power goes out. Also, if you wanted a long term solution and you didn't have a whole home backup system, you might split some of the pv to the non backed up side. This way you still get the same backfeed, just reduced solar generation when the grid goes down.

Yes. It would have been best if your solar/Powerwall installer (Tesla?) had offered such an option with the system. Installing three Powerwalls would have helped, but at a price!

So I plan to switch back my lights in the house to regular bulbs.

That'd be a real step backwards in terms of energy efficiency and convenience, so if I were in your shoes, I'd first try to work out a solution with Tesla and/or your Powerwall installer. Moving some of your solar breakers out of the backed up loads subpanel would be a good first step, unless you want to add two more Powerwalls! In software, it would be great if Tesla could limit the maximum frequency to 63 Hz instead of 66 Hz for compliant inverters, and support a maximum charge setting. Tesla needs to hear our constructive feedback.

Now, having a maximum charge setting (i.e., 80%) wouldn't be a total panacea even if the Powerwall(s) can handle all of the solar output, as the Powerwalls would eventually reach 100% during a sufficiently long outage. But it would buy time, and most outages are fairly short. In an outage, the Tesla Energy Gateway could even alert us via the phone app when the batteries are almost full, and perhaps suggest manually flipping the solar breaker(s) in order to maintain "normal" power output at 60 Hz.

 

[PBBear]

Well.. I am glad I found this post.
I was doing a proof of concept a couple of days ago to my neighbors. The PW2 was charged at 100%, the house was using about 1.3Kw, the panels were generating about 11Kw, 9.7Kw was sent back to the grid.

I shut down the main, and BOOM. All LEDs in the house start flickering (everything is LED). My USP backups start beeping, and the LEDs that were off can't be turned on. I had to turn all lights off obviously. But this is a disaster.

If you were generating 11Kw, the sun must have been out and strong, one wonders why the lights were on in the first place!
The frequency shift is a problem only when the sun is shining and the panels are producing - and at these times, I would think the effect on lighting would be the least of the issues .

But yes, a less brute-force frequency shift would be an improvement. One method might be to hit 66Hz for one second only, and then reduce to 63Hz. If the inverter starts producing power again, only then raise the frequency back to 66Hz (as clearly the inverter is not compliant with modern standards). Then the households with modern inverters would only have the severe reaction you described for a single second only.

 

[FGC92]

Can you set your PW2 to not charge more than 80%?

HI !

No. I am in the USA / NJ and we do not have this function.
I will call Tesla though, they say they accept feature requests..

 

[FGC92]

The issue is that the Powerwall tells the PV system that it is done charging by shifting the grid frequency.

Regardless what level you tell the battery to stop at, when it does sense its full, it will turn off the PV by shifting frequency.

Generally its a bad idea to design these systems with more than 5-7 kw of PV generation for each Powerwall. One potential work around is to manually disconnect some of your PV breakers when the power goes out. Also, if you wanted a long term solution and you didn't have a whole home backup system, you might split some of the pv to the non backed up side. This way you still get the same backfeed, just reduced solar generation when the grid goes down.

Yes, I should have thought about that. I have everything in the house back up beside the AC units and the pool pump.
Each AC uses 2Kw. I think the maximum output of a PV2 is 5Kw. If it's the summer, why not. But winter would not work for me.

 

[FGC92]

If you were generating 11Kw, the sun must have been out and strong, one wonders why the lights were on in the first place!
The frequency shift is a problem only when the sun is shining and the panels are producing - and at these times, I would think the effect on lighting would be the least of the issues .

But yes, a less brute-force frequency shift would be an improvement. One method might be to hit 66Hz for one second only, and then reduce to 63Hz. If the inverter starts producing power again, only then raise the frequency back to 66Hz (as clearly the inverter is not compliant with modern standards). Then the households with modern inverters would only have the severe reaction you described for a single second only.

Yes, it was a sunny day, and as I wrote, I was doing a proof of concept to my neighbors, showing them that well.. if the grid goes off, everything stays on in the house :/

I have a question though. When the inverters (In my case 2 x SOLAR EDGE SE7600H - US) turn off, what keeps them off ?
I think my solution will be to turn the inverters off if we are in the middle of the day. There is a soft off switch on those inverters, but when I try it, it takes a couple of minutes before it totally shuts down.

 

[Vines]

I have a question though. When the inverters (In my case 2 x SOLAR EDGE SE7600H - US) turn off, what keeps them off ?
I think my solution will be to turn the inverters off if we are in the middle of the day. There is a soft off switch on those inverters, but when I try it, it takes a couple of minutes before it totally shuts down.

They are constantly sensing grid voltage and frequency. If they sense that the voltage and frequency is good for 5 minutes, then they turn on.

The new rule 21 compliant inverters have some extra granularity, but I don't know when Tesla will try to utilize this.

 

[NinjaVece]

My wife and I have had our 6.3kW system with a Powerwall 2 for almost a year now. In this (we will call it) year, power has gone out quite a few times for short periods of time, but generally it's been while we weren't home. Well, since December we've had the power drop out for an hour and a half in December and then a short stint of a few minutes a few days ago that we were home for. Now, in our house, I have a few things hooked up to individual backups as well. These are things like our modems, routers, TV, and PC. These are Cyberpower battery backups plugged directly into the wall. Well, both times we've been home, we noticed that the battery backups are thinking they lost power from the wall and causing them to run on their battery! The power is running on backup, our lights are on, other outlets that are not on the Cyberpower battery backup are working FINE. But the Cyberpower units will not notice that there is still power coming from the wall. As soon as it swapped from grid/solar power to the Powerwall, the Cyberpower units would switch to their battery. I have tried unplugging the units, but it's as though that outlet is dead to them. But then I'd plug in a light and BOOM. There is power there!

We wanted to keep our individual battery backups working so that if and when the Powerwall runs out of juice during a longer outage, we can keep our internet running as long as possible. Do you guys think it has to do more with the Cyberpower units or the Powerwall feature? The Cyberpower units are probably nearing the end of their life in general (I think they're about 5 years old each) and I'm thinking of getting new ones anyways. But I don't want to if I'm going to run into the same issue as before.

Let me know if you guys need any additional info. I'm happy to provide additional specs.

Thanks!

Raiderxx, see this thread for a very well documented history of this issue...

Powerwall 2 + UPS Connundrum - and solution

 

[Lloyd]

Well.. I am glad I found this post.
I just got a new solar panel system installed (14.3Kw) with one PW2.
I was doing a proof of concept a couple of days ago to my neighbors. The PW2 was charged at 100%, the house was using about 1.3Kw, the panels were generating about 11Kw, 9.7Kw was sent back to the grid.

I shut down the main, and BOOM. All LEDs in the house start flickering (everything is LED). My USP backups start beeping, and the LEDs that were off can't be turned on. I had to turn all lights off obviously. But this is a disaster.

This is what I figured out in this scenario.
When the PW2 is fully charged, it will send 65.9Hz frequency to the house (and the inverters, so they can shut down).
The PW2 will discharge until it reaches 90%. At this point, the frequency goes down to 60Hz, everything works fine.
The inverters will restart, and the battery will charge again. But I have an issue here because I generate 11Kw, the battery can only take 5Kw intake, and my house is using 1.3Kw
Once the PW2 reaches 98%, we are going back into flickering mode.

So I plan to switch back my lights in the house to regular bulbs.
I wish Tesla explained this to me at the time. I'd never have sign up to have PW installed I think.

I believe if you install "Dimmable" Led's this problem will go away

 

[power.saver]

Dimmable lights (LED or other) work by chopping a part of the AC sine wave to reduce power. They do not alter the frequency. The very small power supply in LED lamps has a tight operating tolerance and 66Hz is outside of it.

This happened to me and I call Tesla to complain, and they said they have received a lot of questions about this, but it won't be fixed until "enough" people complain about it. So if this bothers you, by all means call and complain that you don't like/want/need the 66Hz operation damaging your home electronics and making your lights flicker.

 

[FGC92]

I believe if you install "Dimmable" Led's this problem will go away

No, all my lights are LED Dimmable, and all flicker.

 

[FGC92]

Dimmable lights (LED or other) work by chopping a part of the AC sine wave to reduce power. They do not alter the frequency. The very small power supply in LED lamps has a tight operating tolerance and 66Hz is outside of it.

This happened to me and I call Tesla to complain, and they said they have received a lot of questions about this, but it won't be fixed until "enough" people complain about it. So if this bothers you, by all means call and complain that you don't like/want/need the 66Hz operation damaging your home electronics and making your lights flicker.

I will email them right now.

 

[shs1]

I can certainly confirm that my dimmable LEDs also blink. What worries me the most is things with synchronous motors like the compressor on my refrigerators and freezers that may not do well with 66 Hz. I know the air circulation fan on my fireplace shuts off when it sees 66 Hz.

 

[Lloyd]

Looking at the specifications for SMA string inverters, they do not shut off until they see 66hz.

 

[power.saver]

What SMA inverters? All my SMA string inverters are UL1741 compliant and only operate on 59.4-60.5Hz power. Shifting to 66Hz is way overkill for them, and any other compliant inverter. I would like to know what inverters do operate so far out of the normal frequency range.

 

[Vines]

None of my datasheets for SMA inverters since 2012 show 66 allowable grid frequency. Not sure.

 

[shs1]

I also have SMA inverters and have looked at the spec sheets. What I see is the the fAC Start Delta is 61 Hz and the fAC Limit Delta is 62 Hz (assuming 60 Hz base frequency). That should mean that at 61 Hz the inverter would start to limit its output and that output would go to 0 by 62 Hz. I earlier referred to this frequency range as the Frequency Shift Power Control (FSPC) "polite" mode, and in this mode the inverter is supposed to be ready to increase output as soon as the frequency drops. I also see that fAC Delta+ is 64.5 Hz which is supposed to instruct the inverter to disconnect from the grid or the "rude" FSPC mode. Once disconnected, the inverter won't likely try to reconnect for at least 5 minutes.

The question that was discussed earlier in the other thread is to what extent do the SMA inverters follow the full FSPC protocol when in the grid connected mode as opposed to the off-grid mode that is optimized for charging batteries? Especially in California where I have been told Rule 21 may restrict FSPC if grid tied. However, I am pretty sure that I saw the "polite" mode working in earlier PW2 firmware releases, but that was a while ago. Obviously if the inverters shut down by 62 Hz, we would likely not be having this discussion.

 

[Lloyd]

None of my datasheets for SMA inverters since 2012 show 66 allowable grid frequency. Not sure.

https://files.sma.de/dl/27676/SBxx-1XP-US-40-GridServices-TI-en-15.pdf

I stand corrected. There is a ride through, and an absolute shut down. Explained below.

2.3 Grid Support Depending on Power Frequency "Low/High Frequency Ride-Through" Two thresholds both for minimum power frequency and maximum power frequency are defined in accordance with UL 1741 SA during grid support in dependence of the power frequency "Low/High Frequency Ride-Through (L/H FRT)". Each maximum threshold may be exceeded and each minimum threshold may be undershot for a certain time. The permitted ranges for exceeding or falling below the set frequency are derived from these thresholds and time frames. Frequency (Hz) Time (s) 0.10 1.00 10.00 100.00 1000.00 55.00 56.00 57.00 58.00 59.00 60.00 61.00 62.00 63.00 64.00 HF2 HF1 NN LF1 LF2 Ride-Through High Frequency Curve Ride-Through Low Frequency Curve Must Trip High Frequency Curve Must Trip Low Frequency Curve Figure 2: Ranges for exceeding or falling below the set frequency during "Low/High Frequency Ride-Through" Designation Description Must Trip High Frequency This curve specifies the thresholds within which the shutdown process of the inverter must be completed when permitted frequency is exceeded. Must Trip Low Frequency This curve specifies the thresholds within which the shutdown process of the inverter must be completed when permitted frequency is undershot. Ride-Through High Frequency This curve specifies how long the inverter must continue feeding in when permitted frequency is exceeded. Ride-Through Low Frequency This curve specifies how long the inverter must continue feeding in when permitted frequency is undershot. The inverter continuously checks the power frequency. The inverter continues to feed in up to a set point in time (Ride Through) when the frequency is exceeded or undershot and then starts the shutdown process. The time within which the shutdown process must be completed is saved in the inverter via an adjustable parameter defining the time interval before the latest possible shutdown time (Must Trip). The grid support in dependence of the grid frequency is activated by default. You can configure the thresholds via the parameters listed in the following table. The inverter always operates in "Mandatory Operation" mode during grid support in dependence of the grid frequency