How to tell if my Tesla Energy solar system isn’t producing up to spec?

[Az_Rael]

TLDR: I am only seeing a peak output of around 8.5kW for my 11.34kW system. Tesla says it is normal. Is it?

Been keeping an eye on my system just through the Tesla app and the minimal data available on MySolarCity. (I don’t know that I am savvy enough to hook up any of the more sophisticated monitoring options like PV Output.). I posted this in another thread, but thought I should start my own vs continuing to hijack an unrelated thread.

I have two arrays on my home, one facing South with 12 315W Panasonic panels and one facing East with 24 315W Panasonic panels. The southern array is connected to a 3.8kW Delta inverter and the eastern array is connected to a 6.6kW Delta inverter. My home has zero shade issues, and most days are full sun with no clouds.

The highest peak production I have ever seen out of the eastern array is 5.8kW and it normally maxes out just over 5kW. My southern array normally peaks at 3.5kW which seems pretty good compared to its rated numbers. I have never once seen inverter clipping on my production graphs, even though I probably should by the straight numbers and it being summer.

I called Tesla Energy and they show no errors and that my current production is at 91% of predicted for the ~ 2 months the system has been turned on. They said they don’t worry about a system until it gets closer to 60-70% of predicted production (!) and that my system is perfectly fine. They told me not to worry about the peak kW numbers and that they don’t really mean anything. I asked why I had never seen clipping on my inverter, but got nowhere with that line of questioning. I also got nowhere asking why the two arrays performed so much differently.

I did run PVWatts for the eastern array. I assumed premium panels and entered the correct pitch and azimuth but left the losses estimates as the default. It estimates June production should be 1387kWh AC, my actual was 1191kWh.

Is this within the normal variation of solar installs? My panels are dusty (it hasn’t rained in months) - I rinsed them off with a hose a month ago, but wasn’t able to do a real good job on the large array.

Here is the current dirt level on the larger array. Think the bird droppings might be the issue? I would have to hire a service to get up there to really clean them. It hasn’t rained here in months.




Here are some screen caps of the Tesla app for yesterday vs Solar City’s tool


And here is a shot from my best production day so far on a cool day in June:



Thoughts? Do I actually have a potential problem, or am I just worrying over nothing?

 

[mspohr]

Your South array is 12*315=3780 max. and your observed peak is 3.5 kw... seems just fine.
Your East array is 24*315-7560 max. (6.6 kW inverter) and your observed peak is 5.8 kw... seems fine since this is facing East, not South. It will never have peak rated output.
Summer heat impacts generation. I find I get the highest peaks in spring and fall.

I am compulsive about watching my solar output with PVoutput and after a while I have learned what to expect. Some people just install and forget it and others, like me, watch it every day. (Rendezvous Totals 9.300kW | Live Output)
I wouldn't worry. It looks like your system is functioning as designed and installed.
I don't know if your Tesla Energy / Delta system can export to pvoutput but the do have some nice tools there.

 

[Az_Rael]

seems fine since this is facing East, not South. It will never have peak rated output.

That is interesting - I thought the array orientation mattered more for my production over time, not that I would never get peak output on that east array.

Now that I look at my photography tool, I see that this time of year, the sun is only at 40 degrees above the horizon at an azimuth of 90 degrees. My array is sitting at a 26.6 degree tilt based on my roof pitch of 6/12. If I am doing my geometry right, the sun needs to be at 63 degrees above the horizon to be 90 degrees from my panels. That occurs at around 11:15AM at an azimuth of 113 degrees (SSE):

I guess I will have to hope the system eventually catches up with my PV Watts estimates on an annual basis (it is currently underperforming). That is the tool I used to size the system, so I hope I didn’t mess up there.

 

[Dan123]

Considering that your sub-arrays are facing in different dirrections, 8.5kw is pretty good, and it is close to what one would expect.

You can do a rough calculation on PVWatts Calculator
You need to do two separate calculations, treating each sub-array as a separate system, and then add the numbers.

 

[mspohr]

That is interesting - I thought the array orientation mattered more for my production over time, not that I would never get peak output on that east array.

Now that I look at my photography tool, I see that this time of year, the sun is only at 40 degrees above the horizon at an azimuth of 90 degrees. My array is sitting at a 26.6 degree tilt based on my roof pitch of 6/12. If I am doing my geometry right, the sun needs to be at 63 degrees above the horizon to be 90 degrees from my panels. That occurs at around 11:15AM at an azimuth of 113 degrees (SSE):

View attachment 317376




I guess I will have to hope the system eventually catches up with my PV Watts estimates on an annual basis (it is currently underperforming). That is the tool I used to size the system, so I hope I didn’t mess up there.

Yes, the sun will be at 90 vertical angle to the panels at 11:16 but the sun for most of the year is not hitting the panels at a 90 horizontal orientation. In the summer, the sun is to the North of the panels, in the winter it is to the South (at your location). At the equinox, it looks like you might have 90 horizontal and vertical (and therefore theoretical max insolation) at solar max.
Here's a handy tool to visualize the sun's path throughout the year.
SunCalc sun position and sunlight phases calculator

 

[Az_Rael]

You can do a rough calculation on PVWatts Calculator
You need to do two separate calculations, treating each sub-array as a separate system, and then add the numbers.

I did that - I actually sized the system initially using PV Watts, running it as two separate systems. For June the 24 panel system underperformed PVWatts and the 12 panel system over-performed it.

June production vs PVWatts estimates:

24 Panel array: 1191kWh actual, 1387kWh estimate .
12 Panel array: 777kWh actual, 672kWh estimate.

I know this is just one month, and I guess I will keep watching it. I am just surprised to be underperforming against PVwatts right out of the box.

 

[mspohr]

I did that - I actually sized the system initially using PV Watts, running it as two separate systems. For June the 24 panel system underperformed PVWatts and the 12 panel system over-performed it.

June production vs PVWatts estimates:

24 Panel array: 1191kWh actual, 1387kWh estimate .
12 Panel array: 777kWh actual, 672kWh estimate.

I know this is just one month, and I guess I will keep watching it. I am just surprised to be underperforming against PVwatts right out of the box.

You're getting both overperforming and underperforming on your two systems.
PVwatts (and all other calcs) are estimates and there are lots of variables that can cause significant variation (weather, dirt on panels, temperature, mounting, etc.).
I wouldn't worry. It looks like you're getting about what was estimated.
Also, patience. Give it a year or two to see the real results and in the meantime, enjoy your solar power.

 

[cr0ntab]

That is interesting - I thought the array orientation mattered more for my production over time, not that I would never get peak output on that east array.

Now that I look at my photography tool, I see that this time of year, the sun is only at 40 degrees above the horizon at an azimuth of 90 degrees. My array is sitting at a 26.6 degree tilt based on my roof pitch of 6/12. If I am doing my geometry right, the sun needs to be at 63 degrees above the horizon to be 90 degrees from my panels. That occurs at around 11:15AM at an azimuth of 113 degrees (SSE):

I guess I will have to hope the system eventually catches up with my PV Watts estimates on an annual basis (it is currently underperforming). That is the tool I used to size the system, so I hope I didn’t mess up there.

Nice, what tool is that?

 

[Az_Rael]

Nice, what tool is that?

The photographers ephemeris. Great app for phones, or you can use it on the desktop. Wonderful for landscape photographers!

 

[Az_Rael]

Just an update to this saga. Despite everyone telling me my system was "fine" including several Tesla reps, I finally got a hold of someone who looked at my data and agreed to escalate my case to tech support. About 1 week later I got a call that they needed access to my inverters so I booked a time for yesterday.

Turns out the section of 6 hot panels I could see on my thermal images were wired incorrectly causing some problem with the RSD. The guy spent about 2 hours on my roof fixing the wiring. I am already seeing the results today after the fix yesterday evening. (Weather has been exactly the same. No clouds)


Moral of the story: trust your instincts and you have to be a thorn in Tesla Energy's side to get service unless your system is so broken even the first line rep can tell.

 

[Krebnarb]

What communication avenues did you use to reach out to Tesla Energy to ultimately have them look at your problem? I'm having a similar issue. I have a 16kw array, and under optimal conditions (high noon, no clouds in June), I'm getting max 9kw output.

There was a CT issue in the beginning where the power walls were not charging from Solar, which they "fixed" by flipping the CT software switch, but I've read they should not do that, but rather physically fix the CT wiring. I don't know if that's related to this issue of low production. Really need someone to come out and take a look.

Thanks for your advice!
Wen

Just an update to this saga. Despite everyone telling me my system was "fine" including several Tesla reps, I finally got a hold of someone who looked at my data and agreed to escalate my case to tech support. About 1 week later I got a call that they needed access to my inverters so I booked a time for yesterday.

Turns out the section of 6 hot panels I could see on my thermal images were wired incorrectly causing some problem with the RSD. The guy spent about 2 hours on my roof fixing the wiring. I am already seeing the results today after the fix yesterday evening. (Weather has been exactly the same. No clouds)


Moral of the story: trust your instincts and you have to be a thorn in Tesla Energy's side to get service unless your system is so broken even the first line rep can tell.


View attachment 338176

 

[jjrandorin]

Not sure this will help you but another piece of data I guess. I have an 11.2kw system and have a peak output close to what you posted(8.5-9). This happened as we hit the really hot weather in June/July in Texas. Before that it would produce frequently 10kw’s plus so the heat has reduced the efficiency. Understanding that we are in different locations and probably a host of other factors. Yesterday we had a total production of 71kWh’s.

You might not have noticed, but @Krebnarb made a new post in a thread that was almost 3 years old at the point when their post was made, so the issue you are responding to was resolved back then (september of 2018).