Expected Behavior During Grid Outage

[Matt-FL]

Last Saturday at about 2:30pm (mostly sunny day), we had a grid outage for about an hour. I seem to have had an abnormal experience during this timeframe.
The system switched over to 'grid outage' and powerwalls, without issue. I honestly didn't even notice, except for our UPS batteries started beeping as they don't seem to like the powerwall power cleanliness.
When I checked on the app, I saw that the batteries had taken over, but solar went to zero production - at first I thought because my inverters were rebooted.
However, 39 minutes into the outage, my solar was still showing zero production.

About 30 minutes later, still during the outage, my panels came back online. About 10 minutes later or so, the grid came back online.

You can see from the daily generation graph the drop during the day, approximately an hour.

I know when I simulate a grid outage, I don't lose solar. This was the first daytime outage I've experienced, so just curious if this is 'as it should be' or if something is amiss.

 

[getakey]

if your PWs are at or close to 100%, the PV will shut down. There has to be some "room" for any excess solar to go if not used by the house

 

[Matt-FL]

Great info, thanks for the clarification! I guess later in the day when more power was being used, it could engage the PV.

 

[jjrandorin]

he system switched over to 'grid outage' and powerwalls, without issue. I honestly didn't even notice, except for our UPS batteries started beeping as they don't seem to like the powerwall power cleanliness.

What @getakey said, as far as the production. Your solar production would start again once your powerwalls had dropped some. As far as the quote above, its not power "cleanliness" its the frequency, and thats by design to stop the solar from producing.

In a very " high level / TL ; DR" manner..... Regular power runs at 60hz, by default powerwalls shift power to 65hz when off grid when they are full to shut off pv, many items dont like 65hz power, and you can request Tesla lower this frequency shift some to compensate.

 

[Matt-FL]

Interesting, so the frequency is something Tesla can adjust remotely? lol, was just thinking about how long that conversation with Tesla support would take before they even understood what I was talking about. Great products, but support is... lacking.

 

[jjrandorin]

Interesting, so the frequency is something Tesla can adjust remotely? lol, was just thinking about how long that conversation with Tesla support would take before they even understood what I was talking about. Great products, but support is... lacking.

Here is the (long) thread about Local UPS and frequency shift:

Powerwall 2 + UPS Connundrum - and solution

^ Awesome thanks so much for the reply! I have a rack mounted Eton already.. so from reading the other posts in the thread, I won't have to change the PW frequency settings.. Actually you might. My PW originally ran at 65 Hz and the Eaton complained - bitterly, and ran down the battery...

teslamotorsclub.com

 

[Matt-FL]

Wow, that was easy. Spun up an online chat with Tesla support and they sent it off to the group to make the change. Said it should be complete in 10 days or less.

Thanks for the tip!

 

[jjrandorin]

Wow, that was easy. Spun up an online chat with Tesla support and they sent it off to the group to make the change. Said it should be complete in 10 days or less.

Thanks for the tip!

Thank the people who blazed the trail in that other thread. I am fully convinced (but have no proof) that the only reason that Tesla is now really aware of this issue and has processes in place for it, are the very people in that thread I linked you to above raising the issue and keeping after it until it was "known, documented, and had a process in place to remedy" within Tesla.

 

[bmah]

In addition to all of the great information above about the Powerwall behavior with full batteries, note that if your solar inverter is producing and there's a grid outage (even with batteries at lower state of charge), you might have an interruption in solar production because the disruption in power makes the inverter shut down temporarily as a safety measure. Typically this would be on the order of a few minutes or so.

Bruce.

 

[cbdream99]

I have the exact same behavior couple of weeks ago. Once tge PW is full, PV will stop, it cannot send excess to the grid as someone maybe working on the line, this is the same behavior if you don’t have any PW, once the grid is down, you are out. It’s interesting to learn about the UPS problem, now I understand why mine beeping periodically.

 

[cwied]

Once tge PW is full, PV will stop, it cannot send excess to the grid as someone maybe working on the line, this is the same behavior if you don’t have any PW, once the grid is down, you are out.

I've always found it curious that this is the justification is used. It seems to me like there's a second, more important reason you can't feed power to the grid when the grid is out: the grid is a load that's much larger than the PV system can handle. If the system tried to connect to the grid during an outage, it would instantly shut down because there's too much load (similar to what happens when an air conditioner that's too large for the Powerwalls to handle turns on during a grid outage). The system might be able to put in enough current to be hazardous for the short time until it shuts down, so it's definitely not safe for the linemen, but this wouldn't last long and then the house would no longer have power either.

 

[GregBallantyne]

I've always found it curious that this is the justification is used. It seems to me like there's a second, more important reason you can't feed power to the grid when the grid is out: the grid is a load that's much larger than the PV system can handle. If the system tried to connect to the grid during an outage, it would instantly shut down because there's too much load (similar to what happens when an air conditioner that's too large for the Powerwalls to handle turns on during a grid outage). The system might be able to put in enough current to be hazardous for the short time until it shuts down, so it's definitely not safe for the linemen, but this wouldn't last long and then the house would no longer have power either.

If your system doesn't shut down rather than putting power to the grid during a grid outage, your connection won't get approved. In a non- solar application, if you leave your main breaker open while running a generator to charge your house, the grid operator can and will kill the generator. Isolation from the grid during an outage while self generating is a requirement, despite any other considerations, so all approved systems are designed this way regardless of curiosity.....

 

[cwied]

If your system doesn't shut down rather than putting power to the grid during a grid outage, your connection won't get approved. In a non- solar application, if you leave your main breaker open while running a generator to charge your house, the grid operator can and will kill the generator. Isolation from the grid during an outage while self generating is a requirement, despite any other considerations, so all approved systems are designed this way regardless of curiosity.....

Totally understood. I'm just saying that there also is no point in trying to run without disconnecting from the grid because it likely won't work due to the draw from the grid. I'm assuming that that this would kill a generator too.
My curiosity is not why they require disconnection, but why the second aspect (that it won't work) is never mentioned when justifying why a self-generation system needs to disconnect from the grid during a power outage.

 

[jgleigh]

The solar inverters also need a stable grid frequency. This is provided by the Powerwalls in an outage, but my understanding is generators don't provide a clean enough frequency to use them with just a solar inverter.

 

[BGbreeder]

The solar inverters also need a stable grid frequency. This is provided by the Powerwalls in an outage, but my understanding is generators don't provide a clean enough frequency to use them with just a solar inverter.

Tesla did (continues to do?) off grid installations that have Powerwalls recharging from generators, so I would suggest frequency stability is not a major problem, especially as Tesla's listed choices of generators aren't all inverter generators, nor models widely known for their frequency stability. I would comment that in my experience, modern generator designs are pretty good at staying within a couple of hertz over a wide range of loads, and some even better than that.

I think that with the right tuning, a generator could be adjusted to never to go over, say 61.5Hz. Mine run at 60Hz at 50% load, dropping to 58.5Hz at sudden full load, return to 60Hz at full load, and rising toward 61Hz under no/low load, and I haven't done anything special besides taking the time to adjust the frequency and voltage at near 50% and 100% loads.

All the best,

BG

 

[jgleigh]

Tesla did (continues to do?) off grid installations that have Powerwalls recharging from generators

So is the requirement to shutdown solar inverters when the power goes out more political (aka bureaucracy) than technical? Wouldn't surprise me at all.

 

[ArizonaJon]

So is the requirement to shutdown solar inverters when the power goes out more political (aka bureaucracy) than technical? Wouldn't surprise me at all.

Note the "off grid" in what you quoted. Shutting off the power to the grid during a grid down condition is a safety issue.

 

[BGbreeder]

So is the requirement to shutdown solar inverters when the power goes out more political (aka bureaucracy) than technical? Wouldn't surprise me at all.

Nope, as @ArizonaJon pointed out, it is a safety issue to prevent back feeding power to the grid, which could / would cause a variety of safety and equipment issues.

 

[jgleigh]

@BGbreeder Sorry, I meant why can't we have smart transfer switches (like in the Gateway) that allow solar production to continue when the grid is down. Thought that's what we were talking about. I'm well aware of the safety issues and protecting line workers.

 

[BGbreeder]

@BGbreeder Sorry, I meant why can't we have smart transfer switches (like in the Gateway) that allow solar production to continue when the grid is down. Thought that's what we were talking about. I'm well aware of the safety issues and protecting line workers.

Oh, got it. Sorry to miss that.

To answer this question, Enphase makes grid forming microinverters for exactly this use, and any of the off-grid capable string inverters would do this as well. I would say that for most people micro grids are going to be much easier to have/use if the micro grid includes storage. Micromanaging production to match (highly) variable local consumption is not easy, and excludes items with high startup draws.

All the best,

BG