No Solar Production During Grid Outage?

No Solar Production During Grid Outage?

I have a 12.2k system installed with 1 PW2. We recently had a mid-day grid outage that lasted about 20 minutes. During that time, I noticed that the house was properly drawing from the PW2, but I was confused to see that no power from the panels (bright sunny day) was going to the PW2.

I realize that there is a rule about solar production during a grid outage to protect the linemen, but I was told by Tesla that having the PW2 would mitigate that, and that our system could be self-sufficient if the grid went down -- meaning, 12.2k is enough to run our house for the day when the PW2 is included.

Is this normal, for there to be complete shutdown of the ability for the panels to charge the PW2 when the grid is down? That would basically make the entire system pointless during a grid outage - other than pulling from the PW2. What happens with a long-term outage? I want to be able to use the solar production in such a scenario.....

smaches | August 22, 2019

Sounds to me like everything is working as per the stated design. If your PW's are already *full* or near full, the TEG will shut down the DC path from the panels as there is no where for the excess to go. This is absolutely normal. Once the PW's hit their set point (I do not know what it is - you can call tech support if you're curious), the TEG will recharge them and again, shut off the inverter if the grid is still down.
It's like your glass of water at a restaurant. It just sits there for a while. You take a few sips and sooner or later the waiter will come along and fill it back up again.

david.morgan2 | August 22, 2019

@smaches -- thanks for the explanation. I am not certain, but I believe my PW2 at the time was at about 50-60%, so perhaps you are correct that there is a set point for charging.

Which brings up another question - if it is a bright sunny day and I am generating 9kw, is any of that energy able to go directly to the house load, or will it only charge the PW2 and all power used by the house comes from the PW2?

Tesla-David | August 22, 2019

@david.morgan2, I think @smaches stated it correctly. What was the status of your 1-PW2 at the end of the 20 minute outage, and did your solar kick back in after outage? If you are operating in self-powered mode what is your backup level set at. A 20 minute outage should have comfortably covered your home usage unless you were charging EV's or other high usage appliances. We have 13.2 kWh solar system wit 2-PW2's but have not experienced outage in past 14 months, so can't really comment on our experience. We operate in self-powered mode with backup at 20 percent. I would love to experience an outage to see how the PW2's work to cover our needs. We have done a few tests to make sure they work properly, and they operated like advertised.

smaches | August 22, 2019

For example: per the app and at this time, I am generating 2.7kW (it's only 9:40am), and my house load is pulling 0.9kW of that, with the rest being dumped to the powerwalls (I have 2). My walls are at 66% from my usage overnight and will fill to 100% by about 1 or 1:30 if I don't cook a large lunch (lol). Anyway, once full that same excess is dumped to grid.
Yes, the powerwall act like a bridge between the grid and your solar, with the house being the recipient of whatever combination is required to meet the demand (the TEG does all that magic). It is quite a balancing act, for sure....

Tesla-David | August 22, 2019

I would expect your solar would go to cover house loads, and secondarily to charge your PW2. My observations of our PW2's over past 14 months that is what I have been observing.

jrweiss98020 | September 1, 2019

My system was completed last week. While waiting for the PUD to install the Net Meter, I opened the main circuit breaker between the grid and the Backup Gateway (simulated grid outage). PV panels supplied house power and Powerwall recharge, with the house draw taking priority. When Powerwall was fully charged, PV output matched house load. Ran for 2 days like that, with 25-30% drawdown on Powerwall over night and full recharge well before noon.

After Net Meter was installed, all works well. House load, then Powerwall recharge have priority, and the rest goes to the grid. Changeover appears seamless as loads and PV output changes. 0 power bought from grid to date.

rlwrw | September 3, 2019

jrweiss98020 is correct. Panels and Powerwall are on house side of inverter. With grid down, panels are sole source of power. When Powerwall is at 100% only the house is drawing energy from the panels. Panels will still generate at their capacity for that time of the day, but the house will only draw what it needs. The rest... pffft. No place to put the excess energy. Wasted energy until the grid is back up.

nikki.adra | March 24, 2020

If it is an on-grid solar system then the solar system won't be able to generate electricity during an outage. As solar systems require a minimum power supply to run. You can learn more in detail here -

bp | March 24, 2020

rlwrw's answer is correct. When operating off-grid, while the PowerWall is close to 100% full, because there's no where for excess solar power to go, the solar panel power is turned off (by increasing the powerline frequency above 60Hz) until the PowerWall charge level drops enough (below 95%?) to provide a place to store the solar power.

Also note that this switch may take a few minutes, since the Gateway will not rapidly make changes to using the solar or grid power sources (may take 5 minutes for this to happen).

Jones | March 25, 2020

There is another similar thread on this topic - and a key element in how your powerwalls and solar integrate is the PW inverter frequency during a grid outage. During a real outage about a year ago, a portion of my solar (I have three systems totaling 10kW installed at different times over a 12 year period) did not come back on line when the powerwalls kicked in. The synthetic frequency of the PW was interpreted by one of my inverters as "too high" and it refused to come back on line. One other inverter and my micro inverter string were a bit more tolerant and came back on line quickly. A subsequent firmware update resolved this problem and now my entire solar and PW system play well together during an outage. I am currently on v1.45.1

gregbrew | March 25, 2020

Because of the way PWs shut off inverters (by varying the line voltage frequency a bit), any UPS that you use in your house might behave a little wonky. Previously, my particular UPS wasn't happy with the PW frequency, so it didn't switch back to line power under the PW source, depleted its internal battery and removed power from my server. Not a good idea to simply remove mains power from a server, w/o properly shutting it down first. IIRC, 1.43 tightened up the frequency offset of the PWs enough to keep *most* UPS happy. Mine works fine now, on 1.45.2. | March 26, 2020

@gregbrew - I guess I lucked out. My three UPSs work fine when powered from the PowerWalls. I've only had the PWs for a month, and have 1.45.1. At some point when the UPS batteries go bad, I'll likely get rid of them, seeing how the PW switchover is seamless.

bp | March 27, 2020

After Tesla changed the solar cutoff frequency to 61.5 Hz, only one of our UPS boxes fails to work when powered by PowerWalls off-grid with the PowerWalls near full charge.

I've disconnected all but two of our UPS boxes. One UPS is powering our Comcast/TiVo DVRs (that we don't want to reboot during a power change) and our home file server. The other UPS is for a desktop PC that we want to stay running through a power transition. And for both of these UPS uses, we now only need the UPS to provide power for a few seconds through a power transition - so we don't need them to store/provide a lot of power for very long.

Everything else that was on UPS is now off UPS.

Jeff Hudson | April 2, 2020

This is an interesting thread. I have many questions. I am considering purchasing Powerwall(s) to add to my home for protection from grid power outages. I have a Solar PV system. I do not live in a state where Tesla installs but my solar installer is an authorized Tesla installer. I am very pleased with their install of my October 2015 Solar PV system.

Let me start here if you don't mind and then I should probably pose my specific questions using a new thread.

@bp It is my understanding that the Tesla Powerwall is always 100% of the time supplying power to the protected circuits and that a grid power outage is a total non-event insofar as those protected circuits are concerned. In other words, there should not be any power interruption whatsoever that the protected circuits experience. Please enlighten me so that I can move on to the many additional questions I have a need to ask. | April 2, 2020

@Jeff - On the PW, no they are not providing any power 100% of the time, but it's complex. To power your house it can come from the PW, grid, or solar or some combination. For example, if the solar power is great enough to power your home, any excess goes to charging the PW, and if it's more than the PW needs, it goes to the grid. If the grid is lost, the PW turns on so quickly, nothing in the house will notice it. So it is a non-event as far as your house is concerned.

Jeff Hudson | April 2, 2020

Thanks for the quick comment TeslaTap. I understand that the details of how this all operates is complex and that is what I am trying to understand. I also understand the details of any particular system installed at a residence is more than likely somewhat unique. I am at an experience disadvantage here but this is the point where my first question arises. I think there are two divergent types of battery storage scenarios which I think are largely described as either AC coupled or DC coupled. I am still coming to a personal understanding of the ramifications of both types but I think what you have stated might very well be true for one type (DC coupled) but not the other (AC coupled). Please enlighten me and by the way I have more questions.

bp | April 3, 2020

When the grid is running, it is providing the 60Hz signal for all power. When the grid goes offline, the Gateway has to establish the 60Hz signal (or higher to cutoff solar power when the PowerWalls are close to full). This can take up to a few seconds to complete. During this time, there is a brief interruption of power, which can caused devices with processors (computers, routers, DVRs, ...) to reboot if they aren't on a UPS (needed only for a few seconds). | April 3, 2020

@Jeff - I can only speak to my system (new Feb-2020). The Solar array is DC and connects to inverters that produce AC power. Internal to the Powerwalls in the DC battery pack, but external to it is all AC. So the Powerwalls and the output of the inverters are connected and connected to your home all via AC. The external grid is connected through an electric switch that disconnects the grid in the event of a power failure but is otherwise connected via AC to your Powerwall, house and solar inverters.

During the peak of a sunny day, the Solar inverters via AC are powering the house, sending power to the Powerwalls to charge, and the remaining power is going to the grid. When solar power goes away, the Powerwall is powering the house. If there is not enough energy in the Powerwall (usually some level you set like 20%), the house will switch to using the grid. All this is handled transparently and you'll be completely unaware of the various switching going on behind the scenes. These source power switching does not interrupt PC, clocks, etc.

I haven't had a grid failure yet, so I can't state how fast that switchover occurs. I got the impression it switches within 1 cycle (16 ms), but @bp may be right. I'll have to try it and see what happens. It may depend on the system design too. | April 5, 2020

I tested my system last night. I turned off power using the main breakers to simulate a power failure. Powerwall/solar switched immediately. There wasn't even a flicker of the lights and all the clocks remained working. I went for 18 minutes on backup while doing some minor electrical work on the grid side. Power for the house came from a combination of solar and the Powerwalls. So solar is still usable when the power is off. Turning the grid back on also did not create any flicker or effect like resetting clocks.

This is a relatively new system, so perhaps those earlier posters have an earlier design. My prior non-Tesla solar system used microinverters. That sort of system shuts down when power is lost and is one reason I replaced it. | April 5, 2020

"I tested my system last night. " actually 4 pm, I still had some solar generation at that time, cloudy day.

gregbrew | April 5, 2020

If you didn't have a battery back-up associated with your older micro-inverter-based system, it did exactly what any other non-battery backed up system is supposed to do...shut down during a grid outage. This is true of any PV system, regardless of architecture. There are a few inverters out there that have the ability to provide a small load with power during an outage, but they are rare.

Tesla-David | April 5, 2020

I have microinverters and 2 PW2’s installed in June 2018 and have not had any problems with our system operating when I have tested it. Everything operated flawlessly.

Jeff Hudson | April 5, 2020

Everyone, thanks for the information. Let me chew on this for a while as I look for more information. | April 6, 2020

@gregbrew - Yep, my old system did not have battery backup. Back in 2014, it seemed like most systems going in were using microinverters on solar panels.

One thing I didn't expect is getting any solar power on a cloudy day/rain. Raining now, and my new solar roof is still producing 600W. Not a lot, but more than I'm using at the moment. The old system was usually zero power in similar situations.

Atom12 | April 7, 2020

I did not know about Cloud Enhancement Phenomenon. Awesome multi minute burst of energy.

ian | April 8, 2020

Hello folks, I have a recent PW2 and gateway install with 7.3kW of PV. I've seen it working when the grid is off where solar will be used first but what i was wondering is if the powercut is longer, and darkness comes then the PW could easily run to zero over night. The next morning would the system come back up with sunlight or not?


Tesla-David | April 8, 2020

@ian, your PW2 will start charging the following day after your home loads are met by solar PV. I have two PW2's coupled with 13.2 kWh solar PV system, and operate our system in self-powered mode, and can effectively operate with zero grid draws for 9 months of the year. With a single PW2 you will likely run out overnight, but it will recharge the following day when your solar kicks back in. | April 8, 2020

@ian, I'll also add you can set the bottom limit as an additional backup. I think the default is 20%, so if the PowerWall is powering the home during the evening, and gets down to the limit, 20%, it switches to the grid. Now if you have a power outage, it will make that last amount available down to 0%. I hope that makes sense.

bp | April 9, 2020

When off grid and drawing power from the PowerWalls overnight, the Gateway should stop before the PowerWall batteries are completely exhausted, because it's bad for the batteries to completely exhaust the batteries.

If you compare the % charge level displayed in the Tesla app and from the Gateway's web interface, you'll see a discrepancy in the charge levels - this is because the Tesla app assumes there's a portion of the battery pack that will always be held as a reserve - so 0% in the Tesla app likely means the PowerWalls have about 5% of power left.

The Gateway web interface doesn't appear to do this - it appears to show the actual power level in the PowerWalls (0% would mean the PowerWalls are very close to empty).