Wow, did I read that right? 40% over max? Or, if a 12khw system has a typical max of approx 10kw, it could spike up to 14kw? In excess of the size of the system?
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Just Ordered 16.32kW w/2 Powerwalls
- Thread starter Southpasfan
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Wow, did I read that right? 40% over max? Or, if a 12khw system has a typical max of approx 10kw, it could spike up to 14kw? In excess of the size of the system?
I think (but am not sure) that this would be inverter dependent. Meaning, the inverters will only spike up to their rated numbers, and not above that (it would clip above that, I believe).
My system is rated for 8.7kW but my inverter sizes are 4.2 and 3.4 (which is obviously 7.6 or, less than my system rated size of 8.6). I have never seen a spike higher than about 7.4, and thats only for a couple minutes. My panels may be rated for 8.6 but my system never clips either. I get nice, round solar graphs when there are cloudless days.
Thats panel orientation, etc etc. Above my ability to figure out... but basically It depends on the inverter and panel orientation etc. Its unlikely with a system that size on a roof that all panels are getting same amount of sun at a specific time during the day, so I would imagine that the 12kW system with 2 powerwalls "should be" fine, but definitely something to take up with the installer for that home.
As they warn in the commercials, "these results may not be typical - consult your doctor". I have both the solar roof and a number of north-facing panels, so it is conceivable that these factors in some way enhance the relative percentage of the spike. And most of the spikes I've seen are probably around 20%. But I have seen the bigger ones, so it is just something to note is at least possible in some circumstances.
I guess the good news is that if, as has been indicated as this thread has developed, it is possible to manually recover from this kind of issue, it may not be as critical to worry about this kind of outlier event. It probably makes sense to leave some headroom between typical max output and where the system would shutdown, but not necessarily 40%.
So I called in and added a third powerwall. As someone said, "results may not be typical" but what I hope to achieve is:
1. House alone is consuming about 60-70 kwh per day now. Would be less in winter because of A/C.
2. The system should produce about 90-100 per day in summer, which ought to cover filling up PWs and charging cars.
3. Three PW's aim to cover the 20kwh per evening.
4. Three PWs will also be able to accept the expected possible up to 15kw produced by the system at max, without triggering the automatic shut off.
Next up would be the whole how to install it. From the posts I've read might have to study up to understand it.
1. House alone is consuming about 60-70 kwh per day now. Would be less in winter because of A/C.
2. The system should produce about 90-100 per day in summer, which ought to cover filling up PWs and charging cars.
3. Three PW's aim to cover the 20kwh per evening.
4. Three PWs will also be able to accept the expected possible up to 15kw produced by the system at max, without triggering the automatic shut off.
Next up would be the whole how to install it. From the posts I've read might have to study up to understand it.
So I called in and added a third powerwall. As someone said, "results may not be typical" but what I hope to achieve is:
1. House alone is consuming about 60-70 kwh per day now. Would be less in winter because of A/C.
2. The system should produce about 90-100 per day in summer, which ought to cover filling up PWs and charging cars.
3. Three PW's aim to cover the 20kwh per evening.
4. Three PWs will also be able to accept the expected possible up to 15kw produced by the system at max, without triggering the automatic shut off.
Next up would be the whole how to install it. From the posts I've read might have to study up to understand it.
That part is fairly easy (although a lot of people here like to dive into the electrical theory portion of it). You sort of just have to decide where you want them (the powerwalls). The closer to where your Electrical service comes in, the better. Tesla (or whoever you ordered from ) will propose a wall / location based on eiher the site survey they did, or the pictures you submitted if you did the tesla self survey.
If you like where they are putting (the wall, inside vs outside) then your set. if you dont, decide where you want it ,and let them know. Also decide if things like hidden conduit if installing in a garage matter to you, because that may cost more money.
Well, I tried to test this, but it looks like I won’t be able to. If the system is disconnected from the grid, as soon as I turn off one of the powerwalls the frequency is raised to 62.5 which shuts off my inverters. This happens even though the powerwalls were well under full charge (they were at about 50%) and the sun was behind some clouds, so the solar was only generating about 5kW at the time. I left them like this for a few minutes, thinking that it might just be a reaction to the powerwall switching off, but even after a few minutes it kept the frequency at 62.5. As soon as I switched the other powerwalls back on the frequency dropped back to 60 and the inverters came back on after 5 minutes (There’s a 5 minute delay there to make sure the grid is stable before they come on again)
So (b) is easier to answer than (a). Inverters have long been designed to shut off when the grid goes down. This will protect the lineman working to restore the grid in an outage and prevent damage. One of the ways the inverters do this is to monitor the frequency and if it gets too far out of range then it decides that there’s a problem with the grid and shuts down. The powerwalls take advantage of this and when they want to shut off the inverters (such as when they are at 100% and the grid is down) they will raise the frequency so the inverter shuts down.
So the fact that the inverters shut down when the powerwalls raised the frequency is expected behavior and totally normal. However, what I don’t know is why they raised the frequency when some of my powerwalls were shut off. As I’ve been thinking about it, a lot of things seem to happen in 5 minute intervals (when the grid comes back on the gateway waits 5 minutes before using grid power. When the frequency is lowered after being raised the inverters take 5 minutes before they start up again.). I gave it several minutes, but I’m not sure that I waited a full 5 minutes. It’s possible that the system recognized that the powerwall being switched off was an abnormal situation and it raised the frequency to shut off the inverters to prevent any overload while it assessed what happened. I’m wondering if I had given it more time if it would have eventually lowered the frequency back to normal. I didn’t like having the inverters off and wasting all the solar power during a peak generation time, so I wasn’t inclined to just leave it that way for too long this afternoon. But after the sun goes down this evening I’ll go ahead and try to turn off one of the powerwalls again and give it more time and see if the frequency ever comes back down. If it does, then maybe I’ll try the whole experiment again tomorrow afternoon.
So the fact that the inverters shut down when the powerwalls raised the frequency is expected behavior and totally normal. However, what I don’t know is why they raised the frequency when some of my powerwalls were shut off. As I’ve been thinking about it, a lot of things seem to happen in 5 minute intervals (when the grid comes back on the gateway waits 5 minutes before using grid power. When the frequency is lowered after being raised the inverters take 5 minutes before they start up again.). I gave it several minutes, but I’m not sure that I waited a full 5 minutes. It’s possible that the system recognized that the powerwall being switched off was an abnormal situation and it raised the frequency to shut off the inverters to prevent any overload while it assessed what happened. I’m wondering if I had given it more time if it would have eventually lowered the frequency back to normal. I didn’t like having the inverters off and wasting all the solar power during a peak generation time, so I wasn’t inclined to just leave it that way for too long this afternoon. But after the sun goes down this evening I’ll go ahead and try to turn off one of the powerwalls again and give it more time and see if the frequency ever comes back down. If it does, then maybe I’ll try the whole experiment again tomorrow afternoon.
That is quite an answer. You are just the type of homeowner who deserves solar and powerwalls.
OK, so the sun went down and I took a little more time to play with this and I think I’m more confused now than ever. Here is what I found:
Using the power switches on the powerwalls themselves if I turn one powerwall off the frequency immediately jumps to 60.5hz. If I turn two off at the same time the frequency jumps to 62.5hz. I didn’t try turning more than two off at once because I’m not sure a single powerwall would be able to support my house. Originally I had my kill a watt inside and tried turning two off at the same time, then went in and checked, so I assumed that even when one was off the frequency was going up to 62.5. This time I brought the kill a watt out to the garage with me so I could see what happened exactly as it happened. I tried leaving two powerwalls off for more than 10 minutes and the frequency stayed at 62.5 the whole time. When I turned one back on the frequency immediately fell to 60.5, and when I turned the second back on it went back to 60.
After doing that I wondered what would happen if I turned off their breakers instead of turning off the switch on the powerwall, so I tried that. Turning off one or two powerwall breakers had no effect on the frequency. It stayed at 60hz the entire time.
I also wondered what would happen if I turned off the switch on the powerwall at the same time the breaker is off. This proved to be slightly difficult because the breakers are labeled Battery 1 - Battery 4, but there is no indication on the powerwalls themselves to identify which one is which. I figured I’d try turning one breaker off and then turning the powerwalls off with their switch one by one to see if one responded differently so I might be able to identify them that way. But the results I got were a little weird. If I turned one breaker off the frequency stayed at 60. If I then turned off one of the powerwall’s switches the frequency would then go up to 60.5, the same way it did above. If I then turned the switch on the powerwall back on the frequency would drop back to 60... except for one powerwall. For one powerwall when it was turned off the frequency would rise to 60.5, then when it was turned back on the frequency would stay at 60.5. The frequency then stayed at 60.5 until I turned the breaker back on. (The one powerwall that this happened with changed depending on which breaker was off, so I suspect that one is the one that corresponded to the breaker that was off)
So after all that I’m not really sure what to make of it. I feel like there’s enough differences in the way the system behaves when the powerwalls are manually shut off that there’s not really a good way to simulate how things would react in a real two powerwall system. So I guess that in order to test this the only other option is to get enough solar power that I can produce more than 20kW. If anyone wants to donate to that effort, let me know. For the sake of science, of course
Using the power switches on the powerwalls themselves if I turn one powerwall off the frequency immediately jumps to 60.5hz. If I turn two off at the same time the frequency jumps to 62.5hz. I didn’t try turning more than two off at once because I’m not sure a single powerwall would be able to support my house. Originally I had my kill a watt inside and tried turning two off at the same time, then went in and checked, so I assumed that even when one was off the frequency was going up to 62.5. This time I brought the kill a watt out to the garage with me so I could see what happened exactly as it happened. I tried leaving two powerwalls off for more than 10 minutes and the frequency stayed at 62.5 the whole time. When I turned one back on the frequency immediately fell to 60.5, and when I turned the second back on it went back to 60.
After doing that I wondered what would happen if I turned off their breakers instead of turning off the switch on the powerwall, so I tried that. Turning off one or two powerwall breakers had no effect on the frequency. It stayed at 60hz the entire time.
I also wondered what would happen if I turned off the switch on the powerwall at the same time the breaker is off. This proved to be slightly difficult because the breakers are labeled Battery 1 - Battery 4, but there is no indication on the powerwalls themselves to identify which one is which. I figured I’d try turning one breaker off and then turning the powerwalls off with their switch one by one to see if one responded differently so I might be able to identify them that way. But the results I got were a little weird. If I turned one breaker off the frequency stayed at 60. If I then turned off one of the powerwall’s switches the frequency would then go up to 60.5, the same way it did above. If I then turned the switch on the powerwall back on the frequency would drop back to 60... except for one powerwall. For one powerwall when it was turned off the frequency would rise to 60.5, then when it was turned back on the frequency would stay at 60.5. The frequency then stayed at 60.5 until I turned the breaker back on. (The one powerwall that this happened with changed depending on which breaker was off, so I suspect that one is the one that corresponded to the breaker that was off)
So after all that I’m not really sure what to make of it. I feel like there’s enough differences in the way the system behaves when the powerwalls are manually shut off that there’s not really a good way to simulate how things would react in a real two powerwall system. So I guess that in order to test this the only other option is to get enough solar power that I can produce more than 20kW. If anyone wants to donate to that effort, let me know. For the sake of science, of course
Well, Brett certainly did his bit.
I had my initial inspection today for the revised 16.32 with 3 PW system. Guy was nice, did not spot any issues. Confirmed that my cement tile roof posed no problems and that the one vent I told them was not there was, in fact, not there.
The next thing I need to figure out is the initial load on the A/C. Apparently (there is a dedicated thread on this) even though the representation is that 3 Pw's should cover the A/C start up amps, sometimes it doesn't work. I will be learning some stuff about air conditioners.
I had my initial inspection today for the revised 16.32 with 3 PW system. Guy was nice, did not spot any issues. Confirmed that my cement tile roof posed no problems and that the one vent I told them was not there was, in fact, not there.
The next thing I need to figure out is the initial load on the A/C. Apparently (there is a dedicated thread on this) even though the representation is that 3 Pw's should cover the A/C start up amps, sometimes it doesn't work. I will be learning some stuff about air conditioners.
About four hours after the initial inspection I got revised plans with a change or two.
Now we see about permits and quote I think.
Interestingly, moving three panels from the north side to the south side of the roof changed the annual production estimate by 400kwh. Not much difference, but the north and south are fully exposed and the slope is maybe 15 degrees. Huh.
Now we see about permits and quote I think.
Interestingly, moving three panels from the north side to the south side of the roof changed the annual production estimate by 400kwh. Not much difference, but the north and south are fully exposed and the slope is maybe 15 degrees. Huh.
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My guess is the system components like the Gateway are designed with a delay since the grid has a lot of delays in it. It takes a bit of time for mechanical switches to change and for the grid to stabilize after failure events like transformer failure, power lines failing, etc. I would not be too surprised to find out there are rules with multi-minute delays about how fast thing can react to changes.
You’re 90% of the way to a solar roof. At least on that one MP
Yup. This house has a really good roof for solar. Big, flat, no dormers, south facing, and maybe only one neighbor can even see it because it’s in a hill.
Did anyone ever figure anything out on this? I was lurking for awhile hoping Brett’s experiment would work.
Last year, the rep I was working with swore that an 18.9kW system would pair nicely with two power walls. I didn’t end up purchasing, though.
Right now, if I go to the solar roof page, it suggests a 17.5KW roof with 2 powerwalls. What’s up with that? I’m not sure how to resolve this.
Last year, the rep I was working with swore that an 18.9kW system would pair nicely with two power walls. I didn’t end up purchasing, though.
Right now, if I go to the solar roof page, it suggests a 17.5KW roof with 2 powerwalls. What’s up with that? I’m not sure how to resolve this.
I think the answer is "more powerwalls" or a system with 2 inverters where one of them wont run at all when there is an outage. for a system that size I believe you want at least 3 powerwalls, or a minimum of 1 powerwall per 7 ish kW of PV... more doesnt hurt of course. For a system listed at 18.9kW, if its yearly production is at least that, you would want a minimum of 3 powerwalls I would think, and 4 wouldnt be bad either (except on the wallet, lol)
