5 Powerwalls not working as expected in Maryland

[MD38]

Well, not exactly.


First, some background, and apologies in advance for the long post. Our five powerwalls were installed last week (after being ordered last March) in combination with our existing 38kw solar array, which was installed this past September. We use quite a bit of power here on our farm, where our home and business, totaling three occupied/heated/cooled buildings, are located. The solar array should 90 to 100% of our electrical needs over the course of the year. I decided to go the solar/battery back-up route after originally considering back-up generator(s) for grid down scenarios. The economics of backing-up our electrical needs via generator and propane turned out to be as expensive, or more expensive than installing the 5 powerwalls—especially when assuming outages of several days or longer, given the cost to run propane in a generator system that large. And, Maryland has an Energy Storage Tax Credit that 30% (up to $5000 for residential, $75,000 for commercial), which is on top of the Federal credit. So, after doing some research on the powerwalls, it was a no-brainer. I view the solar as an investment, and the powerwalls as insurance.


The solar install was a big project, and has not been exactly smooth sailing, although I am happy overall. We’ve had high grid voltage issues, which along with our large solar array during sunny days, often pushes the voltage above 260, and occasionally above 263. At 263, at least one of our three (3 x 11.4kw) SolarEdge inverters will trip, which then lowers the line voltage below the threshold, which allow the tripped inverter(s) to come back online after about 5 minutes. I’ve been hounding our utility company about the line voltage, which they admit is too high, and they’ve finally indicated that it should be fixed by this Friday. Fingers crossed, but not holding my breath. In the meantime, when I’m paying attention during sunny days, I’ve found that increasing the household electrical loads (e.g., time our laundry to run during peak solar production) reduces the line voltage, usually enough to avoid tripping the solar inverters. Despite these frustrations, I’m very happy with our solar production.


Back to the issue at hand. Everything had been running well with the powerwalls as far as I could tell. We ran through a number of grid-down simulations (first with the installation crew, and later by myself), and the system worked well, with our backed-up circuits all running as planned, including the largest of our hvac systems, a 5-ton heat pump (in which they insisted installing a soft start, even though it likely didn’t need it). The Tesla app also seems to be working right for the most part. Then, yesterday: as solar production was ramping up at ~10:30am, the grid power went out, and the powerwalls failed to kick-on. At the time, grid voltage was high, above 260, and the powerwalls were at 100% SOC. Power was out at our neighbors as well, so it wasn’t only our property. Power was out for only about 5 minutes, and my Tesla app shows that back-up power was on for 3 seconds, although it was difficult to gauge that in real-time. I don’t know if, had the grid power been down for longer, whether the powerwalls would have turned back on by themselves, but everything came back online when the grid power came back. No problems since then, and I've run another simulated grid-down, although I've not tried a simulated outage during peak solar production while batteries are at 100% (will do that today).


So, my questions are:

1. Anyone have any idea what could have caused a failure in the back-up power? Is there a safety mechanism built into the powerwalls that turns them off in a high voltage spike scenario, like what happens with the solar inverters? I wonder if the same thing would have occurred had the powerwalls been at less than 97% charge (thereby able to absorb the solar that was being produced when the power went out, which was a little over 20kw).
2. In a grid down scenario, would the powerwalls turn off the solar panels if the solar panels produce more than what is consumed—i.e., solar is producing 30kw and the 5 powerwalls (which to my understanding can’t charge at a rate of more than 5kw per powerwall= 25kw for 5 powerwalls) plus consumption is less than that?
3. Has anyone figured out how to reliably keep the powerwalls from charging above a certain reserve level, say 70%? I tried a couple different Time-Based settings, where peak prices were set during solar production hours, and the powerwalls still charge beyond the reserve level with excess solar.

If you’ve read through this, I’m impressed and thankful. Any insight would be much appreciated—I’ve already learned quite a bit from this forum.


Matt

 

[Cirrus MS100D]

I’m curious what you find out, have no expert advice to give, but what was your solar production doing at 10:30AM when the power went out? Shouldn’t it have been a combined effort of solar + PW during this outage?

FWIW, our Tesla app always shows “5 minutes” for minimum outages. I think it waits for grid stability in order to switch back, hence 5 min minimum.

 

[MD38]

I’m curious what you find out, have no expert advice to give, but what was your solar production doing at 10:30AM when the power went out? Shouldn’t it have been a combined effort of solar + PW during this outage?

FWIW, our Tesla app always shows “5 minutes” for minimum outages. I think it waits for grid stability in order to switch back, hence 5 min minimum.

Cirrus, solar production was around 21kw at the time the power went down. And, yes, my guess is that the solar panels did play a role in whatever went wrong.

One possible clue I just discovered is that there were several error codes on the SolarEdge inverters, one of which is a "VL-1 Min1" error code 28, which I've never seen before-- I think this is a LOW voltage error. All of the previous errors with the solar inverters had been high voltage ones. Also, I'm seeing that voltage reading since the power outage yesterday have been considerable lower than usual, so maybe the utility company has actually fixed the high voltage issue, and when the were working on the transformer, it did something strange that caused the powerwall failure. Hopefully that's all it was: a perfect storm of a freak voltage spike or drop due to transformer work, along with the right conditions with our batteries and solar. I did another grid outage test 10 minutes ago with the powerwalls at 100% and the solar producing 26kw, and everything worked as expected-- it switched to battery power, and the solar panels were shut down. Solar came back on after I switched the grid power back on.

 

[gpez]

FWIW, our Tesla app always shows “5 minutes” for minimum outages. I think it waits for grid stability in order to switch back, hence 5 min minimum.

The 5 minute outages is not on accident. The Powerwall is certified to meet IEEE 1547 standards and under 4.10.3 return to service after a grid trip is defaulted to 300s - 5 minutes. This means that by default if the Powerwall detects an abnormal grid condition, such as low frequency or high voltage, it will island itself until the grid is normal for at least 5 minutes. Check out https://www.nerc.com/comm/OC_Reliab...rter-Based_Resource_Performance_Guideline.pdf (page 41). I've seen times where the Tesla app says that the system entered backup mode for less than 5 minutes (usually 2-4 seconds) which I believe is due to a grid issue that didn't meet the trip requirements (slightly over voltage, for example).

@MD38 you may have experienced what is called the High Voltage 1 Ride Through (HV1RT). There is a UL certification, UL 1741, which ensures that grid connected devices behave properly under a range of conditions and of course the Powerwall carries this certification. To pass certification devices must respond to abnormal grid conditions within a specific timeframe to protect infrastructure and life. One of those requirements is the HV1RT (http://media3.ev-tv.me/UL-1741-Supplement-A_Webinar.pdf, page 12 and https://www.nrel.gov/docs/fy17osti/67577.pdf page 4) which requires that if the grid voltage is over 110% of nominal and under 120% of nominal the system must disconnect after no longer than 13s. This wide range is due to the fact that grid voltages can fluctuate, especially in high demand or rural areas. If a device experiences HV2, any voltage over 120% of nominal, it must trip immediately. For 240v service the HV1 range is 264v to 288v - super close to your 260v+ that you observed!

Without details of the precise grid voltage, when the grid actually dropped, the inverter's error details, and the Powerwall's status it's really tough to tell exactly what happened. If you're able to dig up a) the exact amount of power being produced by your PVs right before the outage, b) the exact state of charge (SoC) of the Powerwalls when the outage happened, c) the grid voltage right before the outage, d) if the grid actually fully went down from your perspective or if the power being provided by the grid was excessively out of spec, and e) what status the inverters and Powerwall was reporting at the time of the outage.

To your other questions:
2) Yes - when off grid ("islanded") the Powerwalls will adjust your local ("microgrid") frequency based on a formula that takes in to account the Powerwall's SoC, the PV output, and your consumption. Because the frequency ridethroughs are similar to the voltage ridethroughs and its by varying the frequency of the microgrid to instruct the inverters, which very likely are also UL1741 compliant if you're in the US, to shut down as the frequency rises.
3) Which I could help you there - I just use my Powerwall for pure backup

 

[MD38]

Wow, thanks for all the great information.

Without details of the precise grid voltage, when the grid actually dropped, the inverter's error details, and the Powerwall's status it's really tough to tell exactly what happened. If you're able to dig up a) the exact amount of power being produced by your PVs right before the outage, b) the exact state of charge (SoC) of the Powerwalls when the outage happened, c) the grid voltage right before the outage, d) if the grid actually fully went down from your perspective or if the power being provided by the grid was excessively out of spec, and e) what status the inverters and Powerwall was reporting at the time of the outage.

To answer your questions as best I can:

a) Solar was producing 22.5 according to the Tesla app, and 23kw according to the SolarEdge app.
b) The Powerwalls showed 100% charge, but as I understand it, it's not really 100%-- so I don't know the exact SOC.
c) While the Soledge app doesn't have information down to the second, the 3 inverters stagger information every couple minutes. There was a voltage reading of 263.67 just before the power went off.
d) I'm not sure the answer to this question, but I do know that at least two neighboring properties had an outage at the same time as we did. I actually think that the utility company was coincidentally working on the high voltage issue right at that time, and shut the grid down (but perhaps not before sending some whacked-out voltage just prior).
e) All three inverters were shut off due to code 28 "AC Voltage too low (Min 1)" errors, at 10:26am. I don't know what the technical status of the powerwalls were at the time of the outage-- is there a way to tell that? From what I could tell, they simply were not backing-up the home, so everything went dark. I do remember seeing the green lights on the powerwalls, so do not believe that they were completely shut down.

Thanks again.

 

[gpez]

Wow, thanks for all the great information.



To answer your questions as best I can:

a) Solar was producing 22.5 according to the Tesla app, and 23kw according to the SolarEdge app.
b) The Powerwalls showed 100% charge, but as I understand it, it's not really 100%-- so I don't know the exact SOC.
c) While the Soledge app doesn't have information down to the second, the 3 inverters stagger information every couple minutes. There was a voltage reading of 263.67 just before the power went off.
d) I'm not sure the answer to this question, but I do know that at least two neighboring properties had an outage at the same time as we did. I actually think that the utility company was coincidentally working on the high voltage issue right at that time, and shut the grid down (but perhaps not before sending some whacked-out voltage just prior).
e) All three inverters were shut off due to code 28 "AC Voltage too low (Min 1)" errors, at 10:26am. I don't know what the technical status of the powerwalls were at the time of the outage-- is there a way to tell that? From what I could tell, they simply were not backing-up the home, so everything went dark. I do remember seeing the green lights on the powerwalls, so do not believe that they were completely shut down.

Thanks again.

Well your confusion is certainly warranted

There is a way to query the Powerwall directly using the API to get the last fault code but if you've done testing since it's probably gone. Another option is to call Tesla and ask them to look in their data for what the Powerwall reported. If you're tech savvy and feeling adventurous details on how to query the Powerwall directly via command line tools are here: Powerwall 2 Gateway API Documentation (look for "/api/system_status/grid_faults")

I've experienced multiple second outages my house when the PV output is high, Powerwall SoC is high, and house use is low. My thought is that this is the Powerwall's protection mechanism until it is able to fully shut off the PVs, which can take a second or two depending. The two times I've experienced this situation the Powerwall began supplying (and PV was at 0) shortly after.

 

[MD38]

Thank you for all your help gpez, much appreciated. It does appear that they've fixed the high line voltage from the grid, so fingers crossed that this will pave the way for smooth powerwall and solar operations down the road. If not, I have some good information to start troubleshooting, but at the very least, the information you provided will likely help others.

 

[nativewolf]

Thank you for all your help gpez, much appreciated. It does appear that they've fixed the high line voltage from the grid, so fingers crossed that this will pave the way for smooth powerwall and solar operations down the road. If not, I have some good information to start troubleshooting, but at the very least, the information you provided will likely help others.

Great how about you change the thread title from something alarmist to something meaningful, like my 5 new powerwalls are not performing as expected.

My pet peeve on this forum is people posting over the top thread titles that are attention mongering and misleading.

 

[MD38]

Great how about you change the thread title from something alarmist to something meaningful, like my 5 new powerwalls are not performing as expected.

My pet peeve on this forum is people posting over the top thread titles that are attention mongering and misleading.

Fair point-- that certainly wasn't my intention. I just meant that the powerwalls failed to turn on during an actual outage. But the new title is perfectly fine. Thanks.

 

[nativewolf]

Fair point-- that certainly wasn't my intention. I just meant that the powerwalls failed to turn on during an actual outage. But the new title is perfectly fine. Thanks.

Well done. I'm jealous of the 5 powerwalls, congrats!!

 

[jjrandorin]

Op would not have been able to change the title, that would have been done by the Mods. With that being said, I think the new title is more appropriate, but understand where OP was coming from.

OP thanks for sharing.

The energy section here is normally pretty helpful, and I enjoy reading about others installs too, as I usually learn something.

 

[nativewolf]

I agree the energy section is helpful and I only wish it was more active. Some great posters. Gpez reply and MD38 answers were quite informative.

 

[MD38]

Thanks nativewolf and jjrandorin. I'm really happy with the system overall. And, actually, we just had a grid outage about 10 minutes ago that only lasted a few minutes, and the powerwalls responded as designed. Very happy about that. So my guess is that the issue that I originally posted about was a freak occurence, caused by a confluence of extreme voltage fluctuation, and possibly the state of solar production and 100% battery SOC.

 

[woferry]

A question about your large system, are the 3 inverters all on the PW side of the Gateway, or is one on the grid-side?

As you noted, you have more solar production capability than 5 PWs can possibly absorb. So even when the PW batteries are <95% (the PWs start to charge at less than the max 5kW around 95% or higher, this is also when they start adjusting the microgrid frequency to reduce or halt solar inverter production), your solar could overload the system, where certainly the inverters should shut down, but it might also cause the PW to see an overvoltage and also shut down I'd suspect. In the particular case you mentioned above your solar production wasn't quite high enough for this case (though for PWs @ 100% it's definitely too high), but that certainly suggests it could be higher which would be troublesome unless your house is guaranteed to be consuming the excess production so that the PWs wouldn't see it.

In my case, I have two 5.2kW inverters and a single PW. When Tesla designed the system, they put one inverter on the grid side and one on the PW side so that the PW would not be overloaded. Now that does mean if the grid goes down that I lose half of my solar as well, but it's better than losing everything. I hope to add a second PW some day, and at that time I'd move the second inverter to also be on the PW side of the Gateway.

 

[jjrandorin]

. So even when the PW batteries are <95% (the PWs start to charge at less than the max 5kW around 95% or higher, .

I hate to piggy back on a different thread, but I have a question about the "charge at 5kW" statement. I did some searching here but it was inconclusive. I understand the charge rate for the Powerwalls is 5kW, but if you have 2, does that make the max charge rate shown in the tesla app 10kW since they are bundled together in that app?

I ask because I have never seen my 2 powerwalls charge above about 3.3 or 3.4. When I did the googling / checking, some people reported the same, and others did not. My PV system size 8.7 kW, but of course this is winter production for me, so I am only producing about 22-25kW a day. I have 2 inverters. Should I see the Powerwalls charge above 3.4?

Sorry for the hijaack OP, but @woferry mentioning charge rate made me think about it again.

 

[Dan123]

So, my questions are:

1. Anyone have any idea what could have caused a failure in the back-up power? Is there a safety mechanism built into the powerwalls that turns them off in a high voltage spike scenario, like what happens with the solar inverters? I wonder if the same thing would have occurred had the powerwalls been at less than 97% charge (thereby able to absorb the solar that was being produced when the power went out, which was a little over 20kw).
2. In a grid down scenario, would the powerwalls turn off the solar panels if the solar panels produce more than what is consumed—i.e., solar is producing 30kw and the 5 powerwalls (which to my understanding can’t charge at a rate of more than 5kw per powerwall= 25kw for 5 powerwalls) plus consumption is less than that?
3. Has anyone figured out how to reliably keep the powerwalls from charging above a certain reserve level, say 70%? I tried a couple different Time-Based settings, where peak prices were set during solar production hours, and the powerwalls still charge beyond the reserve level with excess solar.

1. The safety mechanism normally kicks when the PW state of charge is low. They shut down and try to restart in 30 minutes, I think. I don't know what caused your PW to shut down. Maybe they tried to shut down the solar inverters, and the inverters didn't turn off right away, so the PWs shut down the grid completely. Are all of your inverters the same model? If not, they may have different settings, so that not all of them shut down at the same frequency. PW uses frequency regulation to turn off inverters, and I think by default it goes up to 62.5 or 63Hz.

2. Yes, they shut down solar production by increasing the frequency. The solar inverters should respond to it.

3. No way as far as I know.

 

[woferry]

I hate to piggy back on a different thread, but I have a question about the "charge at 5kW" statement. I did some searching here but it was inconclusive. I understand the charge rate for the Powerwalls is 5kW, but if you have 2, does that make the max charge rate shown in the tesla app 10kW since they are bundled together in that app?

I ask because I have never seen my 2 powerwalls charge above about 3.3 or 3.4. When I did the googling / checking, some people reported the same, and others did not. My PV system size 8.7 kW, but of course this is winter production for me, so I am only producing about 22-25kW a day. I have 2 inverters. Should I see the Powerwalls charge above 3.4?

Sorry for the hijaack OP, but @woferry mentioning charge rate made me think about it again.

When charging from the grid (no solar) the PWs seem to run at their more optimal 3.3-3.4kW/PW rate. From solar they'll take anything up to 5kW/PW. Mine often hits >95% charge throttling before the solar is >5kW over the house draw, but when that does happen I'll see the PW sitting at 5kW charge and the excess solar going to the grid. I almost certainly have a picture of that somewhere in my thousands of Tesla app screenshots, but not going hunting for it right now.

 

[MorrisonHiker]

When charging from the grid (no solar) the PWs seem to run at their more optimal 3.3-3.4kW/PW rate. From solar they'll take anything up to 5kW/PW. Mine often hits >95% charge throttling before the solar is >5kW over the house draw, but when that does happen I'll see the PW sitting at 5kW charge and the excess solar going to the grid. I almost certainly have a picture of that somewhere in my thousands of Tesla app screenshots, but not going hunting for it right now.

That's exactly what we see on ours as well. Storm Watch kicked in this morning and our 4 Powerwalls started charging at 13.3 kW or 3.3 kW each. We only had three Powerwalls last summer but saw close to 15 kW when charging from solar. Now that we have a 4th Powerwall and more solar, we're hoping to see closer to 20 kW this summer. The household load will still be there but I bet we'll see at least 18 kW going into the Powerwalls on some days.

I do wish there was an easier way to navigate through the daily graphs so that it would be easier to provide screenshots. Hopefully Tesla will eventually allow us to select a day/month/year in the app instead of having to change the graph one day at a time. I know other sites such as pvoutput.org could be used but with a few modifications, the Tesla app could be so much better for reporting.

 

[MD38]

A question about your large system, are the 3 inverters all on the PW side of the Gateway, or is one on the grid-side?

Thanks for the feedback. All three of the solar inverters are together on the powerwall side. So, yes, it sounds like I'd run into an issue if the grid is down and the sun is up, and the charging powerwalls plus the consumption are less than the solar production. But, it sounds like it will be the same as if the powerwalls were at 100% charge, i.e., they'd send a frequency signal to turn the solar off. I guess if there were a longer term grid outage during a sunny stretch, I could just manually shut off one of the inverters to keep that from happening. That's interesting that they put one of your inverters on the grid side-- that would certainly have it's advantages during peak sun during an outage, but a disadvantage when sun is low in the sky, or it is otherwise cloudy.

1. The safety mechanism normally kicks when the PW state of charge is low. They shut down and try to restart in 30 minutes, I think. I don't know what caused your PW to shut down. Maybe they tried to shut down the solar inverters, and the inverters didn't turn off right away, so the PWs shut down the grid completely. Are all of your inverters the same model? If not, they may have different settings, so that not all of them shut down at the same frequency. PW uses frequency regulation to turn off inverters, and I think by default it goes up to 62.5 or 63Hz.

2. Yes, they shut down solar production by increasing the frequency. The solar inverters should respond to it.

3. No way as far as I know.

Thanks Dan. All three inverters are the same model (3 x SolarEdge HD Wave 11.4kw). Regarding limiting the SOC, I've seen some feedback here that by using Advanced- Time-Based- Balanced, with peak set during solar production time, you could prevent the batteries from charging during solar production. I'm not having luck with that, so maybe Tesla has made a change that now, intentionally or not, prevents that work-around.

I hate to piggy back on a different thread, but I have a question about the "charge at 5kW" statement. I did some searching here but it was inconclusive. I understand the charge rate for the Powerwalls is 5kW, but if you have 2, does that make the max charge rate shown in the tesla app 10kW since they are bundled together in that app?

I ask because I have never seen my 2 powerwalls charge above about 3.3 or 3.4. When I did the googling / checking, some people reported the same, and others did not. My PV system size 8.7 kW, but of course this is winter production for me, so I am only producing about 22-25kW a day. I have 2 inverters. Should I see the Powerwalls charge above 3.4?

Sorry for the hijaack OP, but @woferry mentioning charge rate made me think about it again.

No worries. As others have mentioned, the charge rate of 5kw seems to be per powerwall. I've seen a charging rate of 20kw on my 5, so 4kw per powerwall, but I've not had our system up and running long enough to see charging at a rate of beyond that.

I do wish there was an easier way to navigate through the daily graphs so that it would be easier to provide screenshots. Hopefully Tesla will eventually allow us to select a day/month/year in the app instead of having to change the graph one day at a time. I know other sites such as pvoutput.org could be used but with a few modifications, the Tesla app could be so much better for reporting.

I agree. It would also be great if we could have access to things like error codes and more detailed reporting/charting, like is available to users of SolarEdge. That being said, I do really like the Tesla app.

 

[woferry]

Thanks for the feedback. All three of the solar inverters are together on the powerwall side. So, yes, it sounds like I'd run into an issue if the grid is down and the sun is up, and the charging powerwalls plus the consumption are less than the solar production. But, it sounds like it will be the same as if the powerwalls were at 100% charge, i.e., they'd send a frequency signal to turn the solar off. I guess if there were a longer term grid outage during a sunny stretch, I could just manually shut off one of the inverters to keep that from happening. That's interesting that they put one of your inverters on the grid side-- that would certainly have it's advantages during peak sun during an outage, but a disadvantage when sun is low in the sky, or it is otherwise cloudy.

I don't believe that is true. As far as I can tell the PW frequency modulation is based on nothing other than battery SoC, and I don't find that surprising since I don't think it really has anything else to go on. House consumption can change at a moment's notice, as can solar production if the sun comes out from behind a cloud, etc. So AFAIK if the SoC is below 95% (or whatever the true magic number is) and the solar exceeds what the house+PWs can consume (with no grid to absorb the rest), all that will happen is the voltage will overshoot, and while the solar inverters will definitely see this and shut down, I suspect the Gateway/PW's will also see it and probably also shut down. The only hope would be that the voltage the solar trips at is lower than what the Gateway trips at, to have a bit of margin there, but it still depends on just how high (and how quickly) the voltage shoots up. When you're talking about potentially 10kW more solar capacity than PW, I suspect that jump could be very fast/high.

To make things a bit worse in my particular case, the solar production is not balanced evenly across my two inverters (due to the 6 different-sized sets of "arrays" in my roof, facing different directions), and they picked the inverter with the lower production to be the one on the PW side. During the winter this inverter probably produces half the daily output of the other one. So I'm tempted to swap them around, just haven't done so yet.