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

[raiderxx]

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!

 

[MorrisonHiker]

The power frequency from the Powerwalls is probably a little too far from 60 Hz and the Cyberpower UPS takes over to protect devices connected to it. The next time it happens, you can cycle through the display on the UPS and you'll probably find the frequency is off, such as 63 Hz. Alternately, you can try a device such as a Kill-a-watt and see the frequency there.

We've had a few outages since getting our Powerwalls installed. In some instances, our UPS devices were complaining but the power came back on before I could confirm the frequency. I'm not certain but I think if the house is already being powered by the Powerwalls, such as when exporting solar power to the grid during peak, there isn't any issue. I think the UPS notices the issue if the Powerwalls have to take over instantly.

 

[PBBear]

Its a common problem, in-home UPS's not liking the power coming from the powerwall.

Often it can be traced back to the frequency - normal grid is 50Hz (or 60Hz depending on where in the world you are, but go with 50Hz for this example).
However, if the grid drops the first thing the battery controller does is to raise the grid frequency to ~ 55Hz to signal the inverter to stop sending current, in case the solar production was sufficiently high to overload the battery and home. If the battery is not full (or even if it is, but it has discharged down past ~95%), after a few minutes the Tesla gateway will lower the frequency, signalling the inverter to start production again. At night time, it should then keep the frequency at the nominal grid frequency. In day time with solar running, it will cycle the frequency up and down to throttle the solar generation to match the house usage.

UPS's are sensitive to grid line frequency, and will see the 55Hz frequency as 'bad' or 'dirty' power, even though a standard lamp won't have any problem with it.

When it happens again, check any displays on the Cyberpower units to see if they can display grid frequency - and also check the specifications sheet for what frequency range +/- they will accept as good power.

If it happens again at night, the frequency should return to normal within 5 - 10 minutes when the Tesla drops below 95% charge, and the UPS will hopefully lock in then and consider the PW2 power as 'clean', and start recharging as well as backing up the equipment. You'll need to wait a while to see when this occurs.
If it happens again in daytime when solar is running, it will probably cycle in and out.

You'll want your Cyberpower units to provide at least 10 minutes backup time, to rideout the period when the frequency is out of range.

IF this is the issue, then you should be OK - in a longer outage, the Cyberpower units will initially run on battery until the Tesla switches back to 50Hz/60Hz power as it discharges. Then the cyberpower will see good mains power and recharge to full again, while the Tesla battery keeps everything running. If you ever get to the point the Tesla runs out of puff and stops providing mains, the Cyberpower batteries will keep things running for another few minutes.

If you replace the Cyberpower units with new UPSs, looks for units with wider frequency range in the specs sheet. I have Eaton UPSs, and specs sheet identifies the input frequency can range from 46 - 70 Hz working range. It has no problem at all accepting the Tesla power even when it is at 55Hz during a grid failure.

 

[PBBear]

I'm not certain but I think if the house is already being powered by the Powerwalls, such as when exporting solar power to the grid during peak, there isn't any issue. I think the UPS notices the issue if the Powerwalls have to take over instantly.

Almost! If the house is already being powered by the Powerwall at night, so its discharging anyway, there probably won't be a frequency bump if the mains fails.
However, during the day especially if the battery is full and the house is exporting, the PW2 has to instantly raise the frequency to signal (scare!) the inverter to stop producing, as there is nowhere for the excess energy to go. It will keep the inverters stopped until the battery charge drops to ~95%, at which time it will gradually reduce the frequency to allow the inverter to start producing again, balancing the frequency so the inverter output matches the house consumption.

 

[raiderxx]

Its a common problem, in-home UPS's not liking the power coming from the powerwall.

Often it can be traced back to the frequency - normal grid is 50Hz (or 60Hz depending on where in the world you are, but go with 50Hz for this example).
However, if the grid drops the first thing the battery controller does is to raise the grid frequency to ~ 55Hz to signal the inverter to stop sending current, in case the solar production was sufficiently high to overload the battery and home. If the battery is not full (or even if it is, but it has discharged down past ~95%), after a few minutes the Tesla gateway will lower the frequency, signalling the inverter to start production again. At night time, it should then keep the frequency at the nominal grid frequency. In day time with solar running, it will cycle the frequency up and down to throttle the solar generation to match the house usage.

UPS's are sensitive to grid line frequency, and will see the 55Hz frequency as 'bad' or 'dirty' power, even though a standard lamp won't have any problem with it.

When it happens again, check any displays on the Cyberpower units to see if they can display grid frequency - and also check the specifications sheet for what frequency range +/- they will accept as good power.

If it happens again at night, the frequency should return to normal within 5 - 10 minutes when the Tesla drops below 95% charge, and the UPS will hopefully lock in then and consider the PW2 power as 'clean', and start recharging as well as backing up the equipment. You'll need to wait a while to see when this occurs.
If it happens again in daytime when solar is running, it will probably cycle in and out.

You'll want your Cyberpower units to provide at least 10 minutes backup time, to rideout the period when the frequency is out of range.

IF this is the issue, then you should be OK - in a longer outage, the Cyberpower units will initially run on battery until the Tesla switches back to 50Hz/60Hz power as it discharges. Then the cyberpower will see good mains power and recharge to full again, while the Tesla battery keeps everything running. If you ever get to the point the Tesla runs out of puff and stops providing mains, the Cyberpower batteries will keep things running for another few minutes.

If you replace the Cyberpower units with new UPSs, looks for units with wider frequency range in the specs sheet. I have Eaton UPSs, and specs sheet identifies the input frequency can range from 46 - 70 Hz working range. It has no problem at all accepting the Tesla power even when it is at 55Hz during a grid failure.

The power frequency from the Powerwalls is probably a little too far from 60 Hz and the Cyberpower UPS takes over to protect devices connected to it. The next time it happens, you can cycle through the display on the UPS and you'll probably find the frequency is off, such as 63 Hz. Alternately, you can try a device such as a Kill-a-watt and see the frequency there.

We've had a few outages since getting our Powerwalls installed. In some instances, our UPS devices were complaining but the power came back on before I could confirm the frequency. I'm not certain but I think if the house is already being powered by the Powerwalls, such as when exporting solar power to the grid during peak, there isn't any issue. I think the UPS notices the issue if the Powerwalls have to take over instantly.

Frequency! Of course! Thank you both so much, this was exactly what I was looking for! Now my task will be finding two new backups. If the frequency range on the Eaton UPS for example is acceptable, does that mean that it will direct feed that frequency to the PC? I might get a little concerned if "dirty" power starts being sent to my PC. However, thinking about it logically, I'd think that the amount of times this occurs will not be enough to warrant concern... Thanks again!

 

[raiderxx]

Almost! If the house is already being powered by the Powerwall at night, so its discharging anyway, there probably won't be a frequency bump if the mains fails.
However, during the day especially if the battery is full and the house is exporting, the PW2 has to instantly raise the frequency to signal (scare!) the inverter to stop producing, as there is nowhere for the excess energy to go. It will keep the inverters stopped until the battery charge drops to ~95%, at which time it will gradually reduce the frequency to allow the inverter to start producing again, balancing the frequency so the inverter output matches the house consumption.

So, I will have to double check, but I think my battery was LOW on the last outage, becuase I've set it to only discharge during outages (we've been getting a lot of bad weather). So it wasn't discharging at night and the battery was probably around 20%. Wonder if it automatically raises the frequency signal no matter what when the grid drops off?

 

[MorrisonHiker]

Almost! If the house is already being powered by the Powerwall at night, so its discharging anyway, there probably won't be a frequency bump if the mains fails.
However, during the day especially if the battery is full and the house is exporting, the PW2 has to instantly raise the frequency to signal (scare!) the inverter to stop producing, as there is nowhere for the excess energy to go. It will keep the inverters stopped until the battery charge drops to ~95%, at which time it will gradually reduce the frequency to allow the inverter to start producing again, balancing the frequency so the inverter output matches the house consumption.

In the first outage that I had, the batteries were already powering the house, so they weren't full. The UPS devices didn't complain. The second time, the batteries had already stopped powering the house when they reached the reserve. They came back on when the grid went down. That's when the UPS devices were beeping in the middle of the night and alerted me to the outage.

 

[JohnRatsey]

Frequency! Of course! Thank you both so much, this was exactly what I was looking for! Now my task will be finding two new backups. If the frequency range on the Eaton UPS for example is acceptable, does that mean that it will direct feed that frequency to the PC? I might get a little concerned if "dirty" power starts being sent to my PC. However, thinking about it logically, I'd think that the amount of times this occurs will not be enough to warrant concern... Thanks again!

The switch mode power supplies used in computers and and much other electronic equipment are designed to handle a wide range in voltage and frequency. The labels usually say 100-240V 50/60Hz (so the same PSU should work world-wide) but my experience is that they can handle a wider voltage range than on the label and, most likely, a significantly wider frequency range. Wikipedia just says "can tolerate a wide range of power frequencies and voltages" but the basic mode of operation is to chop the incoming power to a high frequency which can then use a very small transformer to change the voltage plus a small rectifier and capacitor to produce DC power.

 

[PBBear]

does that mean that it will direct feed that frequency to the PC?

Depends on the unit, but a 'proper' UPS should condition the power and do a full AC-DC-AC conversion, putting out the clean normal grid voltage and frequency to within a few % accuracy regardless of the input conditions. But you should check the specifications and ask the store to be sure.

 

[shs1]

My situation is much like the OP's with a single PW2 and several local battery backup systems on critical systems. For my phone/networking stuff, modem, router microcell I use 2 deep cycle batteries, a battery charger, and an inverter. That battery backup system is always running off of the battery/inverter so when there is a power failure, there is no switching no the frequency shift either, the batteries just stop charging. My other battery backup stuff starts beeping during a power failure when the PW2 starting putting out 66 Hz and many of the LED lights in the house start blinking as well. Other lights don't work at all. The fan on the fireplace stops. The dogs go crazy with all this going on. I consider this a problem. And it just happened again as I was typing this! SOC was 53%. Fortunately I can switch to my generator remotely and that makes nice clean power that everybody likes.

 

[MorrisonHiker]

Fortunately I can switch to my generator remotely and that makes nice clean* power that everybody likes.

*except for those nasty emissions

 

[shs1]

*except for those nasty emissions

You got me there! We have an all electric house, 2 Tesla cars and the generator is the only fossil fuel we use. I was hoping the PW2 would take over most of my needs during a power failure, but so far it has been less than helpful.

 

[Dave EV]

Depends on the unit, but a 'proper' UPS should condition the power and do a full AC-DC-AC conversion, putting out the clean normal grid voltage and frequency to within a few % accuracy regardless of the input conditions. But you should check the specifications and ask the store to be sure.

Yes - your typical consumer grade or even lower cost business grade UPS does not do any conditioning of the grid power - it simply passes grid power through unless it is out of spec, at which point the UPS will start running of battery. If you want clean, regulated AC power all the time regardless of the input, look for a UPS that says it does "double-conversion" or is "online" as well as has pure-sine-wave output. Avoid "backup" or "line-interactive" UPSs if you want the cleanest power output regardless of the power feeding the UPS.

 

[miimura]

I personally feel that starting in some software release between June and November, the Powerwalls started shifting the frequency away from nominal in conditions that don't warrant it. It should only be shifting the frequency when it needs to curtail the solar. That would be when the solar is either outputting too much power for the Powerwall to absorb (> 5kW per Powerwall) or the Powerwall is nearly full. I have had a couple outages when my Powerwall batteries were low and the Powerwall frequency went high, shutting down my solar. I think the shift was only to 63Hz, so my APC UPS units did not go to battery. I opened a case with Tesla Energy in November but I have not heard anything further. I have also not tested it by simulating an outage by opening my main breaker. I should really do that.

 

[shs1]

My recent experience is during a series of snow storms we have had in the Sierra. I have experienced 5 power failures in the last 2 weeks or so. My SOC has never been above 53% and my solar output has been maybe a kW or less when the failures have happened, as I have had significant snow on my panels and/or it is dark. And yet the PW2 came on at 66 Hz every time. 1.32 firmware.

It seems that there are lots of things in the house that don't like that high of a frequency. Not only do my LED lights either blink or not come on at all, motors like the fan on my fireplace stop working, UPSs beep, and there are other devices that while not damaged need to be power cycled to work again after the power is restored. I hate to think about my refrigerators and freezers.

I really don't see the point of this high frequency output. If the inverter that is part of my network backup system can put out a reliable 60 Hz, I don't know why the PW2 can't. When I bought the PW2, I really wanted something seamless so that if I wasn't home, my wife or house/dog sitter would not have to worry about the power. Yes, the PW2 takes over powering the house quickly, but not well and I have to run down stairs and remotely fire up the generator as fast as possible during every power failure. I am an eco-crazy, Tesla driving vegan and avoid fossil fuels like the plague, but right now I am just glad I have my generator.

 

[SoundDaTrumpet]

... 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.

I assuming you bought the same ones I bought at Costco. Read the manual, there are settings to widen the acceptable frequency and voltage of the power coming in. Perhaps that will help avoid draining the UPS battery during an grid outage with PW powering the home. It be good to know if this helps.

 

[Vines]

This is something Tesla needs to work on for sure. First of all, like others recommended, having individual battery backups is nice in addition to the Powerwall, but they need to be able to work on the 66 Hz that the Powerwall uses as a signal to the PV inverters to curtail production. I do not see this changing, and its actually made worse by storm watch mode, as the battery is automatically charged to capacity. When the battery is above about 85% of capacity, it will frequency shift to ensure that the PV does not come on, as long as the battery is above the threshold. As the solar gets significantly larger than the PW charge capacity, this problem gets worse.

Its not that the Powerwall cannot put out a perfect 60 hz, its that it is programmed to shift its frequency to ensure that PV power generated has somewhere to go.

Imagine this scenario, you have a Powerwall backup system with 1 PW and 8 kW worth of PV. PW are at 90% SoC, and you have a power outage. Most solar production is all or nothing, so if the user is using just 2 kW, what would the Powerwall do with the extra power? It can only use saw 2 kW to charge the batteries (assumed based on 85% SoC). Some of it can be converted to heat through the Powerwall, but not the full 4kW remaining. As it approaches 100%SoC, its ability to use solar power to charge batteries decreases, as allowable charge rates decrease as you approach 100%.

The Powerwall basically turns off the solar by shifting frequency until the house can accept the full brunt of the PV load. Based on others experiences, it does this immediately as a safety mechanism as soon as it switches over, probably until it can get a good handle on the load profile, and then shifts back to 60 hz if it thinks the generation from the PV will be safely used.

Integration with a downstream generator and ATS is also less than ideal. Hopefully further iterations will have the ability to talk to an ATS and integrate in a more useful way without requiring manual user intervention of main breakers or switches, along with manually forcing different SoC minimums to put PW back online. The "backup to the backup" generator will work well until it runs out of gas, but it should be automatic to switch back to Powerwall during a sunny day, after the batteries have discharged, even though the power is still out.

 

[shs1]

I do understand how the PT2 is supposed to uses Frequency Shift Power Control (FSPC) to curtail solar production at high SOC. Last fall, however, I documented several failure modes where the PW2 shifts frequency too aggressively for my SNA inverters – causing them to shut down inappropriately. I had thought that had gotten better, but in the last 2 weeks have had 5 power failures where the SOC was between 8 and 53% and solar production minimal or not at all. and the PW2s started up powering the house at 66 Hz. That did not used to happen. Last fall when I was testing my new installation with a generator, the PW2 frequency would only go high only if there was too much solar production relative to maximum charging rate or a high PW2 SOC. That all seemed to be working fine then, but not so well now.

Let me add a few comments on the integration of my generator into the system. I am attaching a drawing I did in August 2017 to which Tesla agreed that it was OK. It is based on an additional Manual Transfer Switch (MTS) that assures that the PW2 and the generator never see each other. That was Tesla’s requirement and it actually works pretty well and has several of the characteristics that you describe as being desirable.


During a power failure the backup gateway sees the grid go down and takes over providing power to the house. Since the MTS sees power, it keeps the house connected to the backup gateway and PW2. If, however, the PW2 runs out of juice, either based on SOC or excessive load and drops out, then the MTS switches to the generator position and fires up the generator to power the house. In this mode, the PW2 will still see the solar panels and will change off the solar while the house is running off the generator. I certainly saw that happen last fall during initial testing, but I have also seen that if the PW2 goes into Standby because of an overload, it may not put out a feeler voltage/frequency to the solar inverters and they will never fire up. In this automatic mode, when the grid is back up, the backup gateway senses that, as does the MTS and the system returns to the normal on-grid configuration, all automatically. There is also the possibility that in this automatic mode the PW2 may decide it wants to power the house again and could switch the MTS to allow this, but I have rarely seen that happen.

The MTS is labeled as “manual” as it also has a manual mode of operation. If during a power failure, while running off of the PW2, I decide that I would rather run off of the generator, either because I anticipate a load that the PW2 can’t handle, or it is running at a blanketly blank 66 Hz and the house and dogs are going crazy, then I can manually and remotely switch the MTS to generator mode. Again, with the MTS connecting the house to the generator the PW2 still has the opportunity to charge from solar when available. In this manual mode of operation however, it is up to me to manually switch the MTS back to its PW2/grid state when the grid is back up.

Since right now for whatever reason, the PW2 is not charging when it should (I expect a bad CT or 2) and it wants to power the house at 66 Hz, I have been using the manual mode extensively over the last 2 weeks. I have seen the fully automatic mode work as expected in past power failures, and I am sure it would today if I let the PW2 power the house till it drained the batteries.

 

[power.saver]

shs1, after reading your post yesterday, I decided to run a test. I have not had an outage since the upgrade to 1.32 firmware. I was at SOC of 97% and I shut off the main breaker. Solar production was low, and the PW stayed at 60Hz the entire time of my brief test. I think the statement at the end of your recent post

Since right now for whatever reason, the PW2 is not charging when it should

might have something to do with why your PW is jumping to 66Hz immediately upon a power outage.

 

[shs1]

shs1, after reading your post yesterday, I decided to run a test. I have not had an outage since the upgrade to 1.32 firmware. I was at SOC of 97% and I shut off the main breaker. Solar production was low, and the PW stayed at 60Hz the entire time of my brief test. I think the statement at the end of your recent post
.....
might have something to do with why your PW is jumping to 66Hz immediately upon a power outage.

I agree that there is certainly something else wrong with my system and I think it is likely some bad TCs, based on the funny baselines behavior I see in the apps. I figured the 66 Hz problem might be related, but in this thread it seemed that others were experiencing similar problems with high frequencies, I thought it might be related. Given your results (Thanks!) it may be that my PW2's inverters are messed up, or it might be related to the supposed TCs issue. I complained to my local installer a week ago, but...... Sometimes it seems faster to get info from this forum. Thanks again.