[YandSolar]

I have a 20 kw system with 2 powerwalls, installed Aug 2021, started operating on self consumption mode in Oct 21, then finally PTO in March this year. System has been awesome and I haven't had an electric bill since March until now.
On any sunny day my production normally was hitting 15-19kw, even in winter last year. One day this August it dropped by almost half and tops out around 7kw and has never since exceeded this over the last 3 months. Plus, my production has a sudden drop at the same time midday on every sunny day. Online chat and emails with Tesla said everything is performing perfectly but no acknowledgement or reason to why I can't hit above 7kw anymore. Anyone experienced something similar? I expect a gradual reduction going into fall and winter, but this was a sudden change.

 

[Bigriver]

@YandSolar, my first thought was that an inverter stopped working. But Tesla says your system is all functional. They could be wrong, but I would also explore other possibilities. You said that production suddenly drops at the same time each day…. That sounds like a shade issue. Even a small fraction of a shaded panel will essentially shut down the production in that panel. Are some of the panels getting shaded? Could you show a daily production plot, maybe from a recent sunny day and then also going back to early August before the change occurred? Where are you located?

 

[YandSolar]

I am in Maryland. I attached screenshots from sunny days from March, early August (prior to drop) and October. There are a few trees in the neighbor's lot but the leaves are now gone and I don't think shade is a major issue, although might contribute some.

 

[cdhowe]

I experienced a similar but more subtle failure this year. I was closely monitoring our system output on our 9-year-old 9 kW system, and noticed we were rarely getting above 6.5 kW peaks. Now, I know that the sun angle is much lower in the fall and winter than it is in summer, so I computed what the seasonal falloff should be, but I still couldn't explain the drop in power output.

I called my installer (not Tesla) to come out and check out the inverters and the solar strings. The inverters have a 10-year warranty, so I wanted to make sure that any subtle failure was detected and fixed before the warranty ran out.

Sure enough, the installer found that one of the connecting wires between panels was pulled too tight on installation, causing one of the connectors in the string to corrode and finally fail. They replaced the wire and we're back to full power again.

With such a sudden drop off of more than 50% of your peak power, it sounds to me like one of your strings or inverters has become inoperative. I'd have the installers out and check out the system. This is not a small issue, and with such a new system, you should still be under warranty.

-C

 

[YandSolar]

Thank you both for the replies! This is much more helpful than anything I have gotten from tesla support. Next question is if anyone has advice for how to get them to send someone out! So far they have dismissed my concern twice. I think it is obvious there is an issue and was really disappointed to be dismissed, especially with a new are fairly big system. I will ask them to look into the cause you described.

 

[Klaus-rf]

With such a sudden drop off of more than 50% of your peak power, it sounds to me like one of your strings or inverters has become inoperative. I'd have the installers out and check out the system. This is not a small issue, and with such a new system, you should still be under warranty.

^ This.

 

[Ed Woodrick]

While the sun angel is lower, the sun is also much further south and different trees or obstacles may be blocking.
On the seat that I normally sit at, about three weeks ago, the sun finally got South enough to shine directly in during the afternoon. The rest of the year it is further North

 

[cdhowe]

Just to follow up on my prior comment, Ed is exactly right -- you should double check to see if any of your panels are being shaded from the sun during periods of decreased output. We are rapidly approaching the period when the sun is lowest in the sky at high noon (making it "not so high noon"), and the decreased sun angle may put it behind some trees that it hadn't been behind in summer.

To know how low or high the sun is at various times, I recommend using the NOAA solar calculator and looking at the Sun Azimuth output for your periods of decreased output.

ESRL Global Monitoring Laboratory - Global Radiation and Aerosols

The Global Monitoring Laboratory conducts research on greenhouse gas and carbon cycle feedbacks, changes in clouds, aerosols, and surface radiation, and recovery of stratospheric ozone.

gml.noaa.gov

I believe there are some apps that use Google Maps and sun angle to compute possible shade patterns, but I don't remember the URLs any more.

As to how to get someone to come out and do a site visit, I think you simply cite the part of Tesla's solar panel marketing that says you have a 25-year performance guarantee for your solar panels (noted from Tesla's web site), and that 50% peak output is not within spec of that warranty. You should have a document that describes that warranty in great detail, and it almost certainly has information on how to invoke the warranty for service.

And then, should Tesla continue to ignore you (I don't think that will happen), you might give a call to your state's attorney general's office for assistance in getting them to honor the warranty. I had an impasse a few years ago with another company (not Tesla) that it simply refused to resolve, and I was surprised how responsive they became when the Attorney General's Office of Massachusetts gave them a ring to see if they could help me.

-C

 

[YandSolar]

Thanks for this. I like the NOAA solar site, it is a nice resource.
The drop in production in the afternoon is probably attributed to sun position this time of year, and since I was pre‐ PTO last year I don't have a real comparison because my powerwalls were filled by noon and production would shut down as to not feed the grid.
I will focus my service question with Tesla on the inability to reach 8kW or above for the last 3 months. I have attached one more chart from last Nov as comparison, where I was reaching peak production around 17kW.
Thanks!

 

[YandSolar]

Thanks for this. I like the NOAA solar site, it is a nice resource.
The drop in production in the afternoon is probably attributed to sun position this time of year, and since I was pre‐ PTO last year I don't have a real comparison because my powerwalls were filled by noon and production would shut down as to not feed the grid.
I will focus my service question with Tesla on the inability to reach 8kW or above for the last 3 months. I have attached one more chart from last Nov as comparison, where I was reaching peak production around 17kW.
Thanks!

 

[shareef777]

How are your panels setup on your roof? I have a similar setup as yours (19.2kW/2PW+) and have 36 panels east (back of house with zero shade) and 12 west (front of house with slight shade). During the summer the sun was high enough to keep shade at a minimum so as the sun sets later in the day my “curve” remains consistent.

Now that the sun is lower, the west panels are impacted by the shade considerably more. Note this is on a day with zero clouds.

 

[Bigriver]

@YandSolar, on your Nov 5 plot from last year, how was it sending any to the grid if it was pre-PTO?

And your plot from Friday, Oct 21, after the problem started, it shows none to the grid. Is that typical of what you are seeing now? Does the grid ever get any of the solar production? It is almost as if your Oct 21 plot is what I might expect pre-PTO. Did any of your settings get changed?

 

[YandSolar]

@YandSolar, on your Nov 5 plot from last year, how was it sending any to the grid if it was pre-PTO?

And your plot from Friday, Oct 21, after the problem started, it shows none to the grid. Is that typical of what you are seeing now? Does the grid ever get any of the solar production? It is almost as if your Oct 21 plot is what I might expect pre-PTO. Did any of your settings get changed?

I had issues pre-PTO with the system feeding a little to the grid early on, which eventually was resolved. Apparently something was wired wrong with part of the system (don't remember exactly).
Since this issue started in August, I only rarely export anything to the grid but it still happens occasionally. I haven't changed anything in my app settings.

 

[Bigriver]

I will focus my service question with Tesla on the inability to reach 8kW or above for the last 3 months.

I agree this should be the focus. To have examples of peak of 17 kW from this time of year a year ago but only 7 kW now shows a dramatic issue. Please keep us updated on the interaction. I know Tesla Solar customer service can be particularly difficult to get through to.

 

[shareef777]

I would strongly suggest looking into installing this: GitHub - jasonacox/Powerwall-Dashboard: Grafana Dashboard for Tesla Powerwall

Will provide you very specific details. Specifically it'll give you details on the status of each inverter and individual strings. Sometimes you really do have to do the Tesla engineer's job for them to actually get any response.

 

[YandSolar]

Update‐ I spoke with powerwall tech support and was able to get someone to acknowledge that there appears to be a drop that is likely something other than shading or time of year. It is on tier 2 now, but due to backlog the engineers likely won't look at it until december. They also gave me a coupon code for a cleaning service, which I will check out but don't think this is a big contributor since I have hosed them from the ground. I mentioned the faulty wiring that was found in the powerwall inverter pre-PTO, and that someone should come out to open it up and see if there is another manufacturing defect that wore out quickly. The installation crew told me I had one of the 1st powerwall pluses in my area, so a mechanical defect will not be too surprising to me. I will update again once I (hopefully) have a resolution.
Thank you all for the input, it has been very helpful and helped me to push through the early dismissals from tesla tech support.

 

[YandSolar]

Update- Tesla will be out next week to replace inverter

 

[YandSolar]

Update- Inverter was replaced last week and production looked good for 1 day. Now, on a sunny clear day, production is back to a 6kw cap. I spent an hour on the phone and was told it looks like there is a system error causing a production limit as if I were pre-PTO (even though my powerwalls are not close to fully charged). Might take another week for someone to look at it....sigh.....

 

[YandSolar]

Update- Inverter was replaced last week and production looked good for 1 day. Now, on a sunny clear day, production is back to a 6kw cap. I spent an hour on the phone and was told it looks like there is a system error causing a production limit as if I were pre-PTO (even though my powerwalls are not close to fully charged). Might take another week for someone to look at it....sigh.....

Update- service is now scheduled for Jan 11th.

 

[YandSolar]

Update- Tesla came out and inspected everything. I don't understand all of the issues but there was arcing with the inverter, something needs replaced in the harness, 2 MCI (mid circuit interrupters) need replaced. System is now completely off and waiting on parts before scheduling the repair. This has now been an issue for 5 MONTHS and I hope it doesn't impact the longevity of my system.