Low solar production before PTO, how to diagnose possible strings issue

[offandonagain]

I recently got my system installed: 12.8kW solar with 2 PWs (1x PW+, 1x PW). Waiting for PTO now, but the system is operational in self-consumption mode.

My solar output is much lower than expected. Based on PVWatts and Tesla's estimates, I should be getting ~16,000kWh per year. The orientation is not ideal (north-facing roof) but the pitch is low at 2/12, and it's a single contiguous array of 32 panels without much shade. In March, PVWatts expect ~1285kWh or ~40kWh per day. However, what's I'm seeing in the last week is less than 20kWh per day when it's sunny. Peak output is at 3.3kW, at around 1pm. Batteries are at 50% so I don't think solar production is getting capped. A single inverter may be an issue for my setup, but I'm not even close to the 7.6kW max.

I'm going to contact Tesla for help, but based on forums this will be a struggle, especially before PTO. I'd like to diagnose the issue as much as I can before that.

From what I can gather from this forum, this looks like an issue with the strings and/or the Tesla inverter. I have two sets of red/black wires going into the inverter so I think two strings for 32 panels? I attached some photos of the inverter. I also gathered diagnostics from pypowerwall at noon today:

{
    "A": {
        "Connected": true,
        "Current": 7.5600000000000005,
        "Power": 2618.0,
        "State": "PV_Active",
        "Voltage": 347.3
    },
    "B": {
        "Connected": true,
        "Current": 6.08,
        "Power": 122.0,
        "State": "PV_Active",
        "Voltage": 20.1
    },
    "C": {
        "Connected": true,
        "Current": 10.38,
        "Power": 202.0,
        "State": "PV_Active",
        "Voltage": 19.400000000000002
    },
    "D": {
        "Connected": false,
        "Current": 0.0,
        "Power": 0.0,
        "State": "PV_Active",
        "Voltage": 1.5
    }
}

Does this look like only one string is producing and I'm only seeing half the expected output? Any other things I should try before contacting Tesla? It's not clear to me what the proper procedure is for restarting the Tesla inverter.

Thanks for your help!

 

[patrick40363]

What size is the inverter?

 

[offandonagain]

What size is the inverter?

It's a 7.6 kW Tesla inverter. I'm not seeing any inverter clipping.

 

[getakey]

to OP, that is way low. I have 11.8kW system on East/West orientation. More on East than West and I'm getting ~50kWh/day now

 

[patrick40363]

It's a 7.6 kW Tesla inverter. I'm not seeing any inverter clipping.

I have a 12.1 kw solar roof with one 7.6 inverter. Mine has 3 strings and the inverter can handle 4. The system generated 58.7 kw today with about 4 hours of clipping, I used to have a 3KW solar panel system on the north side of my roof. It generated 15.50 kw last year on this day so your system should be producing closer to what mine does. I think they didn't set up your system correctly. I am in northern CA and it was sunny all day.

 

[yblaser]

Yes looks like there is a problem there based on your string data. You have one smaller string, I would guess ~9 panels (based on the voltage) going into 1/A which seems to be producing power. They have a second string going into 2/B and jumpered to the 3/C input. That string is only showing ~40V total which means there is something seriously wrong there. Both B and C should be showing the same current too so the fact that they differ is also wrong. They have also wired the strings into the inverter different from what is typical. I don't know if it matters but normally the large string wired to the #2 lower input and would be jumpered with the #1 input and the second string would go to #3 or #4. Instead they have #2 jumpered with #3 with the second string going to #1.

 

[offandonagain]

Thanks all for confirming the expected output!

Yes looks like there is a problem there based on your string data. You have one smaller string, I would guess ~9 panels (based on the voltage) going into 1/A which seems to be producing power. They have a second string going into 2/B and jumpered to the 3/C input. That string is only showing ~40V total which means there is something seriously wrong there. Both B and C should be showing the same current too so the fact that they differ is also wrong. They have also wired the strings into the inverter different from what is typical. I don't know if it matters but normally the large string wired to the #2 lower input and would be jumpered with the #1 input and the second string would go to #3 or #4. Instead they have #2 jumpered with #3 with the second string going to #1.

This is great info, thanks! Maybe I'll get a clamp meter to confirm the string readings.

Now how to get Tesla to address this before PTO :/

 

[KHYE]

I also got my 10 KW system installed last week. I didn't catch the design which put both east and west facing panels onto the same string (19 panels in total). On installation day, they found out that they had to move one south facing panel to east due to roof space limitation. The designer had to update the design plan and resubmit for permit. I was going to call Tesla today and asked them. But I got a call this morning that the installation team will come on site. They would separate east and west panels into separate strings. They were done in 1 hour or so and I can tell the production is way better now. I got lucky that they made the changes before I asked.

I wanted to see the string data by logging into inverter directly but I couldn't. Were you able to get into inverter before PTO?

 

[offandonagain]

I wanted to see the string data by logging into inverter directly but I couldn't. Were you able to get into inverter before PTO?

I didn't try getting into the inverter. I was able to get the string readings using the /api/devices/vitals API on the Tesla Gateway, as described here:

Powerwall Solar Vitals and String Data for External Inverters · Issue #1 · jasonacox/pypowerwall

This is a cross-reference link to a discussion at vloschiavo/powerwall2#51 on the Tesla Powerwall Gateway /api/devices/vitals endpoint. This issue is to troubleshoot and help provide help getting r...

github.com

 

[offandonagain]

They have also wired the strings into the inverter different from what is typical. I don't know if it matters but normally the large string wired to the #2 lower input and would be jumpered with the #1 input and the second string would go to #3 or #4. Instead they have #2 jumpered with #3 with the second string going to #1.

You're spot on here, the diagram inside the inverter clearly states how this configuration should be wired. 2 jumpered with 3 does not looks like a valid configuration, should be either 1-2 or 3-4.

 

[dho112]

I recently got my system installed: 12.8kW solar with 2 PWs (1x PW+, 1x PW). Waiting for PTO now, but the system is operational in self-consumption mode.

My solar output is much lower than expected. Based on PVWatts and Tesla's estimates, I should be getting ~16,000kWh per year. The orientation is not ideal (north-facing roof) but the pitch is low at 2/12, and it's a single contiguous array of 32 panels without much shade. In March, PVWatts expect ~1285kWh or ~40kWh per day. However, what's I'm seeing in the last week is less than 20kWh per day when it's sunny. Peak output is at 3.3kW, at around 1pm. Batteries are at 50% so I don't think solar production is getting capped. A single inverter may be an issue for my setup, but I'm not even close to the 7.6kW max.

I'm going to contact Tesla for help, but based on forums this will be a struggle, especially before PTO. I'd like to diagnose the issue as much as I can before that.

From what I can gather from this forum, this looks like an issue with the strings and/or the Tesla inverter. I have two sets of red/black wires going into the inverter so I think two strings for 32 panels? I attached some photos of the inverter. I also gathered diagnostics from pypowerwall at noon today:

{
    "A": {
        "Connected": true,
        "Current": 7.5600000000000005,
        "Power": 2618.0,
        "State": "PV_Active",
        "Voltage": 347.3
    },
    "B": {
        "Connected": true,
        "Current": 6.08,
        "Power": 122.0,
        "State": "PV_Active",
        "Voltage": 20.1
    },
    "C": {
        "Connected": true,
        "Current": 10.38,
        "Power": 202.0,
        "State": "PV_Active",
        "Voltage": 19.400000000000002
    },
    "D": {
        "Connected": false,
        "Current": 0.0,
        "Power": 0.0,
        "State": "PV_Active",
        "Voltage": 1.5
    }
}

Does this look like only one string is producing and I'm only seeing half the expected output? Any other things I should try before contacting Tesla? It's not clear to me what the proper procedure is for restarting the Tesla inverter.

Thanks for your help!

I hesitate at having a definitive answer for this because I'm too new here But before I had my PTO, my solar only produced enough to cover a little bit over what I was consuming for my house, and I was confused. As soon as I received my PTO and was sending power back to the grid, my solar production went right up to clipping at the 7.7kW inverter max for about 5 hours a day, producing 65+ kWh a day currently in May.

It seemed like before I was allowed to send power back to PG&E the solar panels were only "allowed" to produce a small percentage over my consumption.

 

[offandonagain]

I hesitate at having a definitive answer for this because I'm too new here But before I had my PTO, my solar only produced enough to cover a little bit over what I was consuming for my house, and I was confused. As soon as I received my PTO and was sending power back to the grid, my solar production went right up to clipping at the 7.7kW inverter max for about 5 hours a day, producing 65+ kWh a day currently in May.

It seemed like before I was allowed to send power back to PG&E the solar panels were only "allowed" to produce a small percentage over my consumption.

I forgot to follow up here, but this turned out to be a wiring issue as suspected -- I sent all the information to my project advisor and someone came a few days later to fix it (basically by wiring things according to the diagram in the inverter). My production immediately shot up from ~3kW to the expected 7.7kW.

You're right that production can be capped pre-PTO to avoid exporting to the grid, that only happens once the powerwalls are full. While powerwalls are charging or you have sufficient house loads to use up all the solar production (e.g. by charging an EV), you can get the same output as after PTO.

 

[uscpsycho]

I hesitate at having a definitive answer for this because I'm too new here But before I had my PTO, my solar only produced enough to cover a little bit over what I was consuming for my house, and I was confused. As soon as I received my PTO and was sending power back to the grid, my solar production went right up to clipping at the 7.7kW inverter max for about 5 hours a day, producing 65+ kWh a day currently in May.

It seemed like before I was allowed to send power back to PG&E the solar panels were only "allowed" to produce a small percentage over my consumption.

Sorry to bump this old-ish thread but I have a question for you. You didn't say if you have any PW. If you do, then what you are describing means that the batteries never really charge because you were only producing as much as you were using. Without PW, the only reason to produce more than you use would be to send power back to the grid which you aren't allowed to do without PTO. So without PW limited production might just be a function of not having anywhere for excess capacity to go rather than any kind of throttling by Tesla.

The reason I ask is because Tesla is telling me that even though I have three PW, my max power generation is limited without PTO and I'm trying to figure out if that is true or if I have a problem that they need to address.

 

[Sam88]

I recently got my system installed: 12.8kW solar with 2 PWs (1x PW+, 1x PW). Waiting for PTO now, but the system is operational in self-consumption mode.

My solar output is much lower than expected. Based on PVWatts and Tesla's estimates, I should be getting ~16,000kWh per year. The orientation is not ideal (north-facing roof) but the pitch is low at 2/12, and it's a single contiguous array of 32 panels without much shade. In March, PVWatts expect ~1285kWh or ~40kWh per day. However, what's I'm seeing in the last week is less than 20kWh per day when it's sunny. Peak output is at 3.3kW, at around 1pm. Batteries are at 50% so I don't think solar production is getting capped. A single inverter may be an issue for my setup, but I'm not even close to the 7.6kW max.

I'm going to contact Tesla for help, but based on forums this will be a struggle, especially before PTO. I'd like to diagnose the issue as much as I can before that.

From what I can gather from this forum, this looks like an issue with the strings and/or the Tesla inverter. I have two sets of red/black wires going into the inverter so I think two strings for 32 panels? I attached some photos of the inverter. I also gathered diagnostics from pypowerwall at noon today:

{
    "A": {
        "Connected": true,
        "Current": 7.5600000000000005,
        "Power": 2618.0,
        "State": "PV_Active",
        "Voltage": 347.3
    },
    "B": {
        "Connected": true,
        "Current": 6.08,
        "Power": 122.0,
        "State": "PV_Active",
        "Voltage": 20.1
    },
    "C": {
        "Connected": true,
        "Current": 10.38,
        "Power": 202.0,
        "State": "PV_Active",
        "Voltage": 19.400000000000002
    },
    "D": {
        "Connected": false,
        "Current": 0.0,
        "Power": 0.0,
        "State": "PV_Active",
        "Voltage": 1.5
    }
}

Does this look like only one string is producing and I'm only seeing half the expected output? Any other things I should try before contacting Tesla? It's not clear to me what the proper procedure is for restarting the Tesla inverter.

Thanks for your help!

Hi I have the same issue, very low production, can you tell me how where to use this code. Thanks

 

[sorka]

I hesitate at having a definitive answer for this because I'm too new here But before I had my PTO, my solar only produced enough to cover a little bit over what I was consuming for my house, and I was confused. As soon as I received my PTO and was sending power back to the grid, my solar production went right up to clipping at the 7.7kW inverter max for about 5 hours a day, producing 65+ kWh a day currently in May.

It seemed like before I was allowed to send power back to PG&E the solar panels were only "allowed" to produce a small percentage over my consumption.

Unless your 7.7 kw array is on a tracking platform, there's no way you were making anywhere near 65kwh / day in May unless you're near a very large reflective surface adding an extra 25%.

 

[taphil]

My 8.16kW array and 7.6kW inverter made 58kWh daily in May. April was 60kWh and June 58kWh.

 

[dho112]

Unless your 7.7 kw array is on a tracking platform, there's no way you were making anywhere near 65kwh / day in May unless you're near a very large reflective surface adding an extra 25%.

This is 10 days this last May. I don't know... Am I reading it wrong? The rest of the days were still all well over 60 though. When the Tesla Energy guy came to check on the workers on the roof he actually made a comment to me that I had probably one of the best suited roofs he had ever seen (orientation and pitch). He said it was nearly perfect. The only one's he saw that were better were articulated arrays and they don't do those.

Addendum: Oh! I have a 9.6Kwh array! The inverter just clips at the max of 7.7! I just saw that you thought I had a 7.7 Kw array now when I reread your reply, but I was talking about the inverter max LoL!

 

[sorka]

This is 10 days this last May. I don't know... Am I reading it wrong? The rest of the days were still all well over 60 though. When the Tesla Energy guy came to check on the workers on the roof he actually made a comment to me that I had probably one of the best suited roofs he had ever seen (orientation and pitch). He said it was nearly perfect. The only one's he saw that were better were articulated arrays and they don't do those.

Addendum: Oh! I have a 9.6Kwh array! The inverter just clips at the max of 7.7! I just saw that you thought I had a 7.7 Kw array now when I reread your reply, but I was talking about the inverter max LoL!

That it explains it Yea, there was a thread a while back where everyone was comparing their max kwh / kw / day production and I'm pretty sure I beat all the other responses but that's not only because I'm optimal for tilt and azimuth but also because I keep my panels clean and have a white roof that reflects up to the panels adding another 5% or so and even then, my 8.16 kw system has only ever achieved 58 kwh in a single day in may with most of the maxes being in the 55 kwh range. I think the 58 kwh day had additional production due to cloud reflection.

 

[sorka]

My 8.16kW array and 7.6kW inverter made 58kWh daily in May. April was 60kWh and June 58kWh.

Unless you have a huge amount of reflected sun in addition to direct sunlight, this is a bit higher than should be possible.

 

[taphil]

I think it’s right at the limit of what’s possible, most ideal orientation and tilt. It matches what I get from PVWatts estimate.