New PowerWall install woes

[jjrandorin]

PV installer provided diagram of system without batteries as they were engaged much earlier, before it was decided to get batteries. Tesla certified installer then provided PW diagram integrated with PV and their only ask was to step 7.7 inverter down to 7.0. Basically, PV design was changed based on Tesla installer recommendation of PW capabilities. I expected PW installer to know battery capabilities, especially as they asked for the inverter change. We’ll see where things end up; hoping for an amicable, quick, and fair solution.

You likely are going to want a third powerwall for that sized solar installation. If it were me, I would lean on the company that installed the powerwall for them to sell you another one at cost (which, I believe they pay the same for powerwalls we do) but do the installation for free since the system is not performing the way you expected.

That is, as long as they did not recommend 3 powerwalls, or you did not tell them in the beginning "I am only interested in 2 powerwalls".

 

[mstgkillr]

Any updates? I'm currently trying size my system.

 

[zƬesla]

Installer is waiting on Tesla Tier 3 to call them back. Tiers 1 & 2 said inverter/PV sizes were not an issue for 2 PWs. Tier 2 originally indicated a possible issue with wiring in GW which installer checked and discounted.

 

[chrisbailey13]

I have a 19.8...Kw PV with 3 powerwalls. I just watched my PV scale down output when the PWs got close to 100% and as soon as they went into standby it ramped back up. As I watched the PV output, it went from 13Kw all the way down to 3 with partial going to the house, PW's and grid at the same time. As soon as the PW's went to standby it ramped quickly back to 14Kw split between house and grid.

 

[charlesj]

I have a 19.8...Kw PV with 3 powerwalls. I just watched my PV scale down output when the PWs got close to 100% and as soon as they went into standby it ramped back up. As I watched the PV output, it went from 13Kw all the way down to 3 with partial going to the house, PW's and grid at the same time. As soon as the PW's went to standby it ramped quickly back to 14Kw split between house and grid.

I would think that if grid is up there would be no need to slow solar energy as excess PV energy would go into the grid and house load is not that much.

 

[Freakyguy666]

1) Take advantage of your inverter's frequency power scaling. Many new PV inverters (and some old ones) are configurable to scale down production based on the grid frequency. SolarEdge inverters all it "P(F) Power Frequency" (https://www.solaredge.com/sites/default/files/application_note_power_control_configuration.pdf, page 6) and Enphase calls it "curtailment" or "ramp down" (https://enphase.com/sites/default/f...Considerations-AC-Coupling-Micros-Battery.pdf, page 6). Since the Powerwall will increase the power frequency during off grid operations to instruct the inverters how to behave you can match the Powerwall's frequency profile with your inverters to ensure that you never exceed the Powerwall limits. This is what I do for my 8.6kW PV system which just barely reaches the PV inverter rating of 6.6kW during the sunniest of days. If your system supports it this is probably the best way to go.

I have 2 SolarEdge 7600s connected to 4 PWs. I notice that when an outage occurs—even with the PWs below 80% charge—the PV resets before resuming production to meet the load from the Home. Typical production is ~12kW and load is ~5kW.

Would the frequency adjustment you described above help to minimize these PV resets during an outage? If so, how would one determine the best configuration?

Incidentally, Tesla have configured/lowered the frequency in PWs to ensure my UPS’s recognize the power as “good” during an outage.

 

[Vines]

I have 2 SolarEdge 7600s connected to 4 PWs. I notice that when an outage occurs—even with the PWs below 80% charge—the PV resets before resuming production to meet the load from the Home. Typical production is ~12kW and load is ~5kW.

Would the frequency adjustment you described above help to minimize these PV resets during an outage? If so, how would one determine the best configuration?

Incidentally, Tesla have configured/lowered the frequency in PWs to ensure my UPS’s recognize the power as “good” during an outage.

PV should disconnect for 5 minutes after an outage. Its built into the UL safety listing, though there appear to be cases where it doesn't.

I would think that if grid is up there would be no need to slow solar energy as excess PV energy would go into the grid and house load is not that much.

Since powerwalls can only charge from the PV there is a wierd behaviour at the top of the PW charge profile.

Here's my educated theory: As they near 100% capacity the PW ability to take a charge is reduced below the normal 3-5 kW charge rate. The PV is still pumping out its full rated amperage. I believe this is built into the software of the GW, but what I don't understand is why the excess PV doesn't just feed loads, if the PW can only take for instance 1kW charge rate and you have 10 kW extra production. why reduce PW output to 1 kW instead of just using the 9kW excess to offset loads or backfeed to the grid.

The Powerwall seems to frequency shift the PV a little bit to reduce the charge rate, so it can finish charging. When they are charged fully the PW lets things go back to normal.

 

[BrettS]

Here's my educated theory: As they near 100% capacity the PW ability to take a charge is reduced below the normal 3-5 kW charge rate. The PV is still pumping out its full rated amperage. I believe this is built into the software of the GW, but what I don't understand is why the excess PV doesn't just feed loads, if the PW can only take for instance 1kW charge rate and you have 10 kW extra production. why reduce PW output to 1 kW instead of just using the 9kW excess to offset loads or backfeed to the grid.

The Powerwall seems to frequency shift the PV a little bit to reduce the charge rate, so it can finish charging. When they are charged fully the PW lets things go back to normal.

I’m not sure this is quite right. Remember that the frequency shift only happens when you are off grid. If you are on grid then the powerwalls will charge all the way up to 100% with no frequency shift. Any excess solar production will be used to offset loads or backfeed into the grid. In fact the powerwalls couldn’t frequency shift while you were on grid even if they wanted to as they have to match the grid frequency.

However, when you are off grid the frequency shift happens as they approach a full state of charge. And it does so because there is nowhere for the excess production to go. Since you are off grid it can’t be backfed into the grid, and there isn’t enough load to offset the production or the powerwall state of charge wouldn’t be increasing. When you are off grid the solar power goes to the load first and the powerwalls are only charged with excess production.

In my experience this starts when the powerwalls hit 98%. The frequency will ramp up slowly, starting by just bumping the frequency up to 60.1Hz, then as the powerwalls continue to charge the frequency will increase until the inverters shut off. This is an important consideration because most newer inverters will shut off at 60.5Hz, so even if you have tesla lower the max frequency your system likely won’t go over 60.5Hz.

Once the inverters shut off, then the house will run off of the powerwalls until their charge level drops a bit (in my experience, this happens at about 97%). At that point the inverters will come back on (after their 5 minute delay) and then if there is still excess solar production it will just keep cycling as the powerwalls go back and forth between 97 and 98%.

On a side note, the only time you will hit the max frequency is when you have a power failure when the powerwalls are at 100%. In that case, as soon as the grid goes offline they will raise the frequency to the max since they are already at 100%. After the powerwalls drop down to about 97% then they will lower the frequency and allow the inverters to come back online. And this time it will work as above where they will slowly increase the frequency as they start charging again, topping out at 60.5Hz when the inverters shut off.

 

[wjgjr]

On a side note, the only time you will hit the max frequency is when you have a power failure when the powerwalls are at 100%. In that case, as soon as the grid goes offline they will raise the frequency to the max since they are already at 100%. After the powerwalls drop down to about 97% then they will lower the frequency and allow the inverters to come back online. And this time it will work as above where they will slowly increase the frequency as they start charging again, topping out at 60.5Hz when the inverters shut off.

I agree with everything you said, except perhaps this. Before PTO, when the PWs would fill, I saw a frequency rise to 63 Hz. I was not logging all the data, so I do not know if it went higher, but definitely well above 60.5 Hz. And our inverter (Delta Solivia) is supposed to shut off at 60.5 Hz. So, while you may be right about it not hitting the max frequency (which would have been 65 Hz) it was going well above 60.5. I do not know how much this setting is installation or inverter dependent (it is possible that the inverter we have takes longer to shutdown and the gateway kept increasing frequency because of that lag, for example) but I would not count on frequency remaining at or below 60.5 Hz in an off-grid situation where the PWs fill up during the day.

 

[BrettS]

I agree with everything you said, except perhaps this. Before PTO, when the PWs would fill, I saw a frequency rise to 63 Hz. I was not logging all the data, so I do not know if it went higher, but definitely well above 60.5 Hz. And our inverter (Delta Solivia) is supposed to shut off at 60.5 Hz. So, while you may be right about it not hitting the max frequency (which would have been 65 Hz) it was going well above 60.5. I do not know how much this setting is installation or inverter dependent (it is possible that the inverter we have takes longer to shutdown and the gateway kept increasing frequency because of that lag, for example) but I would not count on frequency remaining at or below 60.5 Hz in an off-grid situation where the PWs fill up during the day.

Obviously I’m only speaking from my experience, so it’s possible that other systems may behave differently because of other inverters or other variables. But from my own observations of my own system the frequency would never get above 60.6Hz while it was cycling.

It surprises me that they would get as high as 63Hz in your case, but I imagine that it’s possible.

 

[Vines]

I’m not sure this is quite right. Remember that the frequency shift only happens when you are off grid. If you are on grid then the powerwalls will charge all the way up to 100% with no frequency shift. Any excess solar production will be used to offset loads or backfeed into the grid. In fact the powerwalls couldn’t frequency shift while you were on grid even if they wanted to as they have to match the grid frequency.

However, when you are off grid the frequency shift happens as they approach a full state of charge. And it does so because there is nowhere for the excess production to go. Since you are off grid it can’t be backfed into the grid, and there isn’t enough load to offset the production or the powerwall state of charge wouldn’t be increasing. When you are off grid the solar power goes to the load first and the powerwalls are only charged with excess production.

In my experience this starts when the powerwalls hit 98%. The frequency will ramp up slowly, starting by just bumping the frequency up to 60.1Hz, then as the powerwalls continue to charge the frequency will increase until the inverters shut off. This is an important consideration because most newer inverters will shut off at 60.5Hz, so even if you have tesla lower the max frequency your system likely won’t go over 60.5Hz.

Once the inverters shut off, then the house will run off of the powerwalls until their charge level drops a bit (in my experience, this happens at about 97%). At that point the inverters will come back on (after their 5 minute delay) and then if there is still excess solar production it will just keep cycling as the powerwalls go back and forth between 97 and 98%.

On a side note, the only time you will hit the max frequency is when you have a power failure when the powerwalls are at 100%. In that case, as soon as the grid goes offline they will raise the frequency to the max since they are already at 100%. After the powerwalls drop down to about 97% then they will lower the frequency and allow the inverters to come back online. And this time it will work as above where they will slowly increase the frequency as they start charging again, topping out at 60.5Hz when the inverters shut off.

Yea, as I thought about it more it makes less sense. It will be interesting to have a Powerwall system on my own house to be able to test on, and perhaps log what the power is looking like under various conditions. There's something going on that I don't quite understand here, and is demonstrated by @chrisbailey13 Not quite sure what else would cause that behavior?

 

[BrettS]

Yea, as I thought about it more it makes less sense. It will be interesting to have a Powerwall system on my own house to be able to test on, and perhaps log what the power is looking like under various conditions. There's something going on that I don't quite understand here, and is demonstrated by @chrisbailey13 Not quite sure what else would cause that behavior?

The powerwalls are designed to support ramping back the PV output, as long as the inverter supports it. However, it doesn’t appear that tesla normally configures this. (They certainly didn’t in my case at least). However, my solaredge inverters support ramping back production with a feature called P(f). I believe other inverter manufactures support this as well, but it’s probably called something different.

With the solaredge inverters you can define a low frequency level and a high frequency level and it will limit output when the frequency is in that range. For example you could define a low frequency of 60 and a high frequency of 61. As long as the frequency was at 60Hz or less the inverters would output 100% of the solar production. If the frequency started going up then it would scale back. At 60.1Hz it would only output 90% of the solar production. At 60.5Hz it would output 50% of the production, etc, until it got up to 61Hz and then it would turn off.

Because the powerwalls will slowly raise the frequency as they approach 100% you can configure your inverter to scale back production as the frequency increases and (theoretically) at some point it will reach an equilibrium where the amount of power the inverters are producing is equal to the amount of power your house is drawing.

However, in practice this may be a bit difficult as the inverter scales based on percent of current production. So as clouds come and go or as the sun moves across the sky the output will still be changing. Additionally the power demand from the house will go up and down. But the system can use this to scale back solar production as the powerwalls get close to being fully charged.

I spent a little time trying to configure this on my system, but eventually I gave up. The first problem I had was that even if I set the high frequency level to, say 61 or 62Hz the inverters would still shut off when the frequency got to 60.5Hz. Apparently that cutoff was defined elsewhere in the settings. So at that point I could only work with the range of 60Hz to 60.5Hz and that just wasn’t enough range to really make this effective. The frequency would get up to 60.5 before the inverters had a chance to react and scale back and they would just shut off instead. Additionally I really wanted to set the low frequency level to like 60.2 or 60.3 just because I didn’t want my solar production scaling back if the utility happened to be sending power at a slightly higher frequency than normal, but that would just make the scale back range even smaller.

In the end I decided that it just didn’t matter. It seems a little more elegant to allow the system to scale back production, but really it will be no different one way or the other. In one case the system might run at 50% power for a while and in another case it might cycle on and off for a while, but both cases it will produce the same amount of power and have the same amount of power ‘lost’.

 

[Freakyguy666]

Obviously I’m only speaking from my experience, so it’s possible that other systems may behave differently because of other inverters or other variables. But from my own observations of my own system the frequency would never get above 60.6Hz while it was cycling.

It surprises me that they would get as high as 63Hz in your case, but I imagine that it’s possible.

perhaps you have previously contacted tesla and asked them to reduce the frequency while others have yet to do so.

 

[BrettS]

perhaps you have previously contacted tesla and asked them to reduce the frequency while others have yet to do so.

No, what I’m seeing is more than that. Tesla did reduce my max frequency, but they only reduced it to 62.5Hz, not 60.5Hz.

But what I’m seeing happen during an outage as I monitor it with my Kill-A-Watt is that as the powerwalls approach their max state of charge is that the frequency slowly rises. It will start at 60.1, then go up to 60.2, then continue as the powerwalls get more and more charged. However, once it hits 60.5Hz my inverters shut off. My inverters (and I believe all modern inverters) are programmed to turn off at 60.5Hz. Since the inverters are shut off and the powerwalls are no longer charging the powerwalls no longer need to continue increasing the frequency, so it doesn’t go above 60.5Hz.

I’ll try to double check this on the next sunny day. I’d love to see other people testing it with their systems as well.

 

[Freakyguy666]

No, what I’m seeing is more than that. Tesla did reduce my max frequency, but they only reduced it to 62.5Hz, not 60.5Hz.

But what I’m seeing happen during an outage as I monitor it with my Kill-A-Watt is that as the powerwalls approach their max state of charge is that the frequency slowly rises. It will start at 60.1, then go up to 60.2, then continue as the powerwalls get more and more charged. However, once it hits 60.5Hz my inverters shut off. My inverters (and I believe all modern inverters) are programmed to turn off at 60.5Hz. Since the inverters are shut off and the powerwalls are no longer charging the powerwalls no longer need to continue increasing the frequency, so it doesn’t go above 60.5Hz.

I’ll try to double check this on the next sunny day. I’d love to see other people testing it with their systems as well.

I’m not sure that “all modern inverters” cut-off at 60.5Hz. Maybe that’s the discrepancy.

 

[wjgjr]

I’m not sure that “all modern inverters” cut-off at 60.5Hz. Maybe that’s the discrepancy.

I mentioned above in my counter-example that my inverter does report to shutoff at 60.5 Hz. So, at least in this case it is more than that. I could imagine the response time of the inverter could be a factor or maybe Tesla has found that my inverter does need a stronger signal to shut off, despite its specifications. It also may just be that there is some variability in how things are configured by Tesla.

 

[jboy210]

Unfortunately, I cannot see the output of individual inverters. But according to the stickers and manuals, my Delta M-series inverters have a max operating freq of 60.5 Hz

 

[BrettS]

I’m not sure that “all modern inverters” cut-off at 60.5Hz. Maybe that’s the discrepancy.

I believe that the 60.5Hz cutoff is a requirement of the UL1741 standard, which I believe is required in all jurisdictions in the US now. So I suppose it doesn’t necessarily apply to all inverters as off grid inverters don’t need to conform to that standard and perhaps other countries have other requirements. But I believe that any grid connected inverter installed within at least the past couple of years will cut off at 60.5Hz. It is possible that I a mistaken about this though.

 

[Freakyguy666]

I believe that the 60.5Hz cutoff is a requirement of the UL1741 standard, which I believe is required in all jurisdictions in the US now. So I suppose it doesn’t necessarily apply to all inverters as off grid inverters don’t need to conform to that standard and perhaps other countries have other requirements. But I believe that any grid connected inverter installed within at least the past couple of years will cut off at 60.5Hz. It is possible that I a mistaken about this though.

Then why does Tesla default to 65Hz?

Also, how can you be 100% certain that when you called in to request the 65Hz be lowered that they didn’t also lower the frequency to 60.5Hz for the outage cycle?

 

[BrettS]

Then why does Tesla default to 65Hz?

I think they do that to err on the side of caution. Like I said, modern inverters are configured to cut off at 60.5Hz, but older inverters may or may not support that standard. Since the outcome of the inverter not shutting off could be dangerous and destructive Tesla wants to be as certain as possible that any inverter that is connected to the system will shut off when it needs to. One of the things they do when they lower your frequency is check your inverter stats to make sure that it will shut off below the new maximum frequency.

Also, how can you be 100% certain that when you called in to request the 65Hz be lowered that they didn’t also lower the frequency to 60.5Hz for the outage cycle?

Because the outage cycle doesn’t have it’s own frequency cut off - it’s self limiting. It simply ramps up the frequency as the powerwall state of charge increases. The frequency will continue to increase until the inverters shut off, which, in my case (and the case of any newer inverter) will happen at 60.5Hz. At that point the powerwalls state of charge is no longer increasing, so the frequency will stop increasing as well.

If for some reason the inverter didn’t shut off at 60.5Hz then the frequency would keep increasing until it did, or until the powerwall hit 100% charged and the frequency got to the max limit that tesla had configured.