Tesla Solar 8.19KW System

[Burn]

I had a Tesla Solar system installed in late Dec 2019. Now that it is summer I don't ever see a peak generation of more then 7.6KW. This is on a full summer day without any clouds. Is it possible that I have some panels that aren't producing? Would Tesla be able to trouble shoot remotely?

Thanks,

Mike

 

[wjgjr]

There are reasons the DC system size doesn't equate to the maximum AC production, but I'm guessing the answer here is that you have a 7.6kW inverter (that is the size of our inverter and would be reasonable for your system size.) When you go to the Tesla app and look at your energy usage for a clear day, is it a smooth curve, or is the top of the curve lopped off (flat) around solar noon? If it is flat, that is a good indicator that the inverter has maxed out and is clipping.

Most likely Tesla intended this and their annual generation estimate reflects the expected clipping.

 

[Burn]

There are reasons the DC system size doesn't equate to the maximum AC production, but I'm guessing the answer here is that you have a 7.6kW inverter (that is the size of our inverter and would be reasonable for your system size.) When you go to the Tesla app and look at your energy usage for a clear day, is it a smooth curve, or is the top of the curve lopped off (flat) around solar noon? If it is flat, that is a good indicator that the inverter has maxed out and is clipping.

Most likely Tesla intended this and their annual generation estimate reflects the expected clipping.

It doesn't "appear" to be clipping. It is fairly symetrical. I've posted a few pictures below.

 

[wjgjr]

I agree, that doesn't look like it's clipping, so this goes back to the fact that an 8.2kW DC system will not generate 8.2kW AC due to a number of "derate" factors, including loss at the inverter, as an example.

Just as a reference, Tesla suggests an 8.2kW system will generate 41-57.4 kWh of energy daily (Solar Panels Monitoring | Tesla Support) at this time of year (likely at that high end) so it seems like your numbers are in range.

 

[Burn]

I agree, that doesn't look like it's clipping, so this goes back to the fact that an 8.2kW DC system will not generate 8.2kW AC due to a number of "derate" factors, including loss at the inverter, as an example.

Just as a reference, Tesla suggests an 8.2kW system will generate 41-57.4 kWh of energy daily (Solar Panels Monitoring | Tesla Support) at this time of year (likely at that high end) so it seems like your numbers are in range.

Ok, thanks for the info.

 

[wjgjr]

Ok, thanks for the info.

I'm sure others may have thoughts as well, but the other thing to look at is if you installed in December, do you have 6 months of data at this point? If so, how close are you to being at half the estimate Tesla provided you for year 1 production? Since those 6 months run roughly from the winter to summer solstice, it should give a decent estimate (assuming weather/cloud cover isn't too different in each half of the year.)

 

[wwu123]

In addition to the system losses mentioned, it may also have to do with geometry. I believe the nameplate rating is when the sun is directly perpendicular to the panel. Depending on your latitude, the angle of your roof/installation, how far off pointed from due south, the day your array is perpendicular to the sun may not be noon on the June 20th, the longest day of the year. And in these summer months, higher temps, panel temp not ambient, because it's summer, will cause a few percent losses.

The highest peak I typically see on my south facing 4kw system is about 3.3kw on a clear, warm summer day, so your number looks pretty good all considered

And I have panel level monitoring so I know I dont have a missing panel or microinverter

 

[GaitherBill]

I would think you would need the sun 100% perfectly lined up on each panel 100% to hit your max.
I know with our 17.9KW system the most I’ve seen is 13.6, just the way she goes with roof mounted panels.

I suppose one of those sun tracking arrays would yield better results.

 

[gpez]

This is one of those things I wish I was better educated about ahead of getting my PV system installed. Not that it would have changed anything, just would have reduced exactly this anxiety and confusion as I'm a big numbers guy

There are so many factors that play in to how your system operates. A system with one inverter will behave differently than a system with microinverters, how often your panels receive maximum sunlight they can handle, their orientation, the time of year, etc. If you have microinverters and different cardinal panel orientations you may never see clipping on your aggregated graph because there will never be a time all of your panels are maxed as the sun travels during the day.

 

[wjgjr]

This is one of those things I wish I was better educated about ahead of getting my PV system installed. Not that it would have changed anything, just would have reduced exactly this anxiety and confusion as I'm a big numbers guy

There are so many factors that play in to how your system operates. A system with one inverter will behave differently than a system with microinverters, how often your panels receive maximum sunlight they can handle, their orientation, the time of year, etc. If you have microinverters and different cardinal panel orientations you may never see clipping on your aggregated graph because there will never be a time all of your panels are maxed as the sun travels during the day.

Something that would be cool for Tesla to do would be to provide the detailed estimates that go into the annual production numbers - I'm thinking the daily "perfect conditions" kWh and the average kWh for the day, based on expected weather, etc. I kind of understand why they don't - they don't want to explain to every customer why their number didn't match "perfect" today (yes, there was that brief cloudy period, haze, etc.) or why they are running low this month (more storms than normal, for example,) but for those of us who do really watch the numbers and try to figure out what is going on, it would definitely help confirm things are actually working as expected (or not, if numbers are way off.) I wonder how much they are tracking this internally, both to refine their estimates for the future, and to proactively detect any equipment issues.

 

[charlesj]

Yep, sun tracking will yield much better results.

Also, roof pitch and direction of major roof angle, time of year, etc.

Micro inverters would give one the ability to monitor each panel performance independent of the others.
I have such a setup and is great.

 

[jjrandorin]

I had a Tesla Solar system installed in late Dec 2019. Now that it is summer I don't ever see a peak generation of more then 7.6KW. This is on a full summer day without any clouds. Is it possible that I have some panels that aren't producing? Would Tesla be able to trouble shoot remotely?

Thanks,

Mike

OP we obviously live in different areas, but if it makes you feel any better, my PV system size is 8.7, and on a typical day right now, my PV numbers look quite a bit like yours.. I generate around 50-55 kWh a day on a sunny day here where I live in Southern california. I have 2 inverters, one is 4.2 and the other is 3.4, but I never see more than about 7kW of peak generation. I have had my system since 2015, and yearly production of my system is between 11,500 and 12,900 kWh, which is on track with what they told me in the beginning.

TL ; DR ... your system performance looks extremely normal and expected to me, who has a system of similar size, in a likely more sunny area.

 

[Burn]

Yep, sun tracking will yield much better results.

Also, roof pitch and direction of major roof angle, time of year, etc.

Micro inverters would give one the ability to monitor each panel performance independent of the others.
I have such a setup and is great.

How do you know if you have a single inverter or micro inverters?

 

[jjrandorin]

How do you know if you have a single inverter or micro inverters?

I have never seen microinverter setup, but my inverter(s) are big boxes on the side of my home. I think the micro inverter setup is different, without the big inverter boxes on the side of your home.

 

[1100MCM]

I have never seen microinverter setup, but my inverter(s) are big boxes on the side of my home. I think the micro inverter setup is different, without the big inverter boxes on the side of your home.

Yes. Micro inverters are small and for my setup they are mounted under each panel so they are not visible. Like some have said, a single inverter would probably be near the electrical panel or mounted somewhere near other electrical boxes or switches for the solar setup.

 

[charlesj]

How do you know if you have a single inverter or micro inverters?

Yes, as mentioned, micros are right under each panel and sends AC to the breaker box.
Hopefully, other micro companies also have a way to monitor power production of each and in total similar to Enphase.
Enphase also gives a number of parameters such as temperature, DC volt and current, AC voltage at each inverter.