New 20kW solar roof install seeing low numbers

[jjrandorin]

If this is to be expected for a 20 kw solar roof at my sunny location in northern CA, it is a bit disheartening that it can basically only handle my AC at this time of the year, no EV charging has been done. I "overbuilt" this system, they recommended a 16 kw system.

You mention you have 2 powerwall+. AFAIK, those inverters are 7.6 each. So, even if you have 20kW of panels, you only have 15.2 of inverters, so your system will never have a peak output of more than your inverters.

You also mention that the orientation is east / west, which isnt optimal (but not much you can do about the direction your home faces, etc). You will have less production during the fall / winter than someone who had the same system size but mostly oriented south.

Your yearly production will likely be fine and should be what you focus on, but you dont have any data to compare to, so its understandable that you are looking at it and trying to figure it out.

I really doubt that there is anything wrong with your system at this point, but as this is fall, and production from PV systems are declining due to sun orientation (see @h2ofun 's post , his peak of 180 per day is down to 80 as an example), you wont really see how much your system can generate at peak output until next april / may.

 

[bushidosunny]

You mention you have 2 powerwall+. AFAIK, those inverters are 7.6 each. So, even if you have 20kW of panels, you only have 15.2 of inverters, so your system will never have a peak output of more than your inverters.

You also mention that the orientation is east / west, which isnt optimal (but not much you can do about the direction your home faces, etc). You will have less production during the fall / winter than someone who had the same system size but mostly oriented south.

Your yearly production will likely be fine and should be what you focus on, but you dont have any data to compare to, so its understandable that you are looking at it and trying to figure it out.

I really doubt that there is anything wrong with your system at this point, but as this is fall, and production from PV systems are declining due to sun orientation (see @h2ofun 's post , his peak of 180 per day is down to 80 as an example), you wont really see how much your system can generate at peak output until next april / may.

Ok, so the ultimate question is:

How does one find out if they are getting what they paid for?

 

[jjrandorin]

Ok, so the ultimate question is:

How does one find out if they are getting what they paid for?

You track your data over time (weeks / months). There is likely a yearly estimate on production, but that production will not be 1/12th of that estimate, monthly. Production from november - January will be, on average, 1/2 of production of april -June.

 

[Big Earl]

If this is to be expected for a 20 kw solar roof at my sunny location in northern CA, it is a bit disheartening that it can basically only handle my AC at this time of the year, no EV charging has been done. I "overbuilt" this system, they recommended a 16 kw system.

How much did you import from the grid on the day you posted a screen shot of?

 

[charlesj]

As a data point about time of year and orientation, I have 41 solar panels that are 300 watts (12.3 kW DC max) with microinverters. Some of the panels are facing south and west and some are not as optimized (kind of like your roof), and my peak generation today in San Diego was 7.2 kW AC just after noon...It is 90 degrees here today with very few clouds...

I think the discussion about your inverters is relevant to see what the max rating is and, therefore, what your inverter(s) will top out at...

Curious about your inverter size as well.

 

[SaveOurPlanet]

Ok, so the ultimate question is:

How does one find out if they are getting what they paid for?

On your purchase agreement there should be a line item "Estimated gross annual electricity production in kilowatt-hours" under section "Site & Design Assumptions for your Purchase", the annual kWh production listed is your target, generally Tesla will under estimate it by 5 to 10% to make sure they will hit that target. You should be able to go back to Tesla if you do not hit that target after one year. I know some people claim that their system hit 100% output of their system, but my system hits only 80% on its best day so far, my active cells are all East facing and I thought it was all wrong but after observing it for several months I understand why, I am sitting on a ridge where i can see the bay and even the Pacific if my house is 50 feet higher and have good sunshine from 7:00am to 7:00pm but the sun is just not hitting the roof at the right angles the whole time. I have 2 PWs and self powered and I think I have exported enough to PG&E to offset my next 6 months low production, so at the end I would hit my target, I hope. I think you should be fine.

 

[wjgjr]

Ok, so the ultimate question is:

How does one find out if they are getting what they paid for?

As @jjrandorin said, it takes time. And, until you get PTO, there may be extra factors. Once you get PTO, there are are a few ways to tell, depending on how much effort you want to put in. Tesla should have given you an annual estimate, and you can just wait for the year after PTO and see if your total reasonably matches.

On a shorter timescale, PVWatts.com is a good resource. It will provide pretty good estimates of what you should expect on a monthly basis. Do note that each roof plane needs to be entered separately (use a spreadsheet to add them up) and also that the numbers will probably be higher than Tesla. What you can do is take the annual PVWatts and Tesla numbers to get monthly Tesla estimates. As an example, if Tesla says you will generate 10 MWh for the year and PVWatts says 11 MWh, then if you take the monthly PVWatts numbers and multiply by 10/11, you will get a decent estimate of what Tesla is expecting for the month.

Note that daily numbers provided by PVWatts should not be used directly - PVWatts calculates its numbers by using historical weather data, so it can show specific days with unexpectedly low or high production, just due to coincidences of past weather. Even on a monthly variance you can see big differences (as, for example, my system did 10% better this September than last, just due to weather.)

I do feel like your numbers might be a bit lower than I would expect, but as others have identified, there are still many variables to look at before making a firm conclusion. This is also the time of year where daily changes are the largest (being near the autumnal equinox) so even comparing day-to-day and week-to-week can show big changes.

 

[h2ofun]

If this is to be expected for a 20 kw solar roof at my sunny location in northern CA, it is a bit disheartening that it can basically only handle my AC at this time of the year, no EV charging has been done. I "overbuilt" this system, they recommended a 16 kw system.

It gets worse, much worse in winter and rain!!!!! I am guessing there will be days my 30kw system will be lucky to do 10kwh for the entire day, which means my batteries will not recharge. Oh well.

 

[BrokerDon]

If this is to be expected for a 20 kw solar roof at my sunny location in northern CA, it is a bit disheartening that it can basically only handle my AC at this time of the year, no EV charging has been done. I "overbuilt" this system, they recommended a 16 kw system.

NoCal would produce less than SoCal solar.

 

[bushidosunny]

How much did you import from the grid on the day you posted a screen shot of?

0.6kwh in the morning because my batteries were 0% at that time.

 

[bushidosunny]

And thank you for everyone giving their time and thoughts on this. What an awesome community!

 

[yblaser]

Your system may be working properly but as mentioned up thread the best way to tell if there is an issue is to log in to the inverter to see the voltage and current on each string. This can tell you if a string is not producing or there are some tiles not working. It is helpful to have your as built design drawings available for reference.

 

[charlesj]

It gets worse, much worse in winter and rain!!!!! ...

What? You are expecting rain?

 

[jboy210]

You can't just add additional active tiles (or panels) to the roof and assume your will get additional production every day. Believe me I tried. Tesla originally sized the roof at 8kW with an option for 12.75 kW. We selected the 12.75 option. Here are some issues we see:

• The downside of the larger configuration is that we have 4+ kW of panels in Northern directions, which is means they only product power 5 months or so of the year. Those are the months on either side of the solar peak day of June 21, which is the day when we see the most power production.
• Even at its peak our solar roof only shows on the application about 9 kW because various parts of roof at optimal angle to the sun at different times. So the additional panels do not show a peak close to the rated 12+ kW total capacity of the roof. What the additional tiles do is cause the roof to produce power earlier and later in the day resulting in a larger daily number of kWh (power), which is the metric that really counts.
• We have shading issues because of trees. This means as we move into fall and summer we not only have less solar production because of the time of year, but also are impacted by the shade.

Some figures. During max daily production (June 21) we see 70+ kWh of production. Today we saw about 30 kWh of production. I expect to see 15 kWh on our lowest day (Dec 21).

 

[arnolddeleon]

Hi,

I'm hoping someboday can help me understand if I have a problem or this is expected. I got a 20kW solar panel installed 3 days ago. It is on normal angle roof, no shade system in northen california. For the last two full sunny days I'm only getting peak 8.9 and 7.8 kW. I thought I should see at least 70-80% of the 20kW but maybe theres something I don't understand.

For what it's worth my 16 kW+ of panels peaked at 7.8 kW yesterday, that's down significantly from just a few months ago. I'm also in the SF bay area. There are many variables, but as others have there is fair chance that there is nothing wrong.

 

[h2ofun]

You can't just add additional active tiles (or panels) to the roof and assume your will get additional production every day. Believe me I tried. Tesla originally sized the roof at 8kW with an option for 12.75 kW. We selected the 12.75 option. Here are some issues we see:

• The downside of the larger configuration is that we have 4+ kW of panels in Northern directions, which is means they only product power 5 months or so of the year. Those are the months on either side of the solar peak day of June 21, which is the day when we see the most power production.
• Even at its peak our solar roof only shows on the application about 9 kW because various parts of roof at optimal angle to the sun at different times. So the additional panels do not show a peak close to the rated 12+ kW total capacity of the roof. What the additional tiles do is cause the roof to produce power earlier and later in the day resulting in a larger daily number of kWh (power), which is the metric that really counts.
• We have shading issues because of trees. This means as we move into fall and summer we not only have less solar production because of the time of year, but also are impacted by the shade.

Some figures. During max daily production (June 21) we see 70+ kWh of production. Today we saw about 30 kWh of production. I expect to see 15 kWh on our lowest day (Dec 21).

What since inverter(s) do you have. YOu cannot get more than their output, no matter how many tiles you have

 

[h2ofun]

For what it's worth my 16 kW+ of panels peaked at 7.8 kW yesterday, that's down significantly from just a few months ago. I'm also in the SF bay area. There are many variables, but as others have there is fair chance that there is nothing wrong.

My 30kw peaked at 13.3kw yeaterday

 

[h2ofun]

Another way to look at this is in July, I produced 4.842 MWh's, but in September, I only produced 3.216MWh;s. And the worse months are coming, with last year in Calif having little rain, I hope it will be even worse than last year, we NEED the rain!!

 

[wjgjr]

You can't just add additional active tiles (or panels) to the roof and assume your will get additional production every day. Believe me I tried. Tesla originally sized the roof at 8kW with an option for 12.75 kW. We selected the 12.75 option. Here are some issues we see:

• The downside of the larger configuration is that we have 4+ kW of panels in Northern directions, which is means they only product power 5 months or so of the year. Those are the months on either side of the solar peak day of June 21, which is the day when we see the most power production.
• Even at its peak our solar roof only shows on the application about 9 kW because various parts of roof at optimal angle to the sun at different times. So the additional panels do not show a peak close to the rated 12+ kW total capacity of the roof. What the additional tiles do is cause the roof to produce power earlier and later in the day resulting in a larger daily number of kWh (power), which is the metric that really counts.
• We have shading issues because of trees. This means as we move into fall and summer we not only have less solar production because of the time of year, but also are impacted by the shade.

Some figures. During max daily production (June 21) we see 70+ kWh of production. Today we saw about 30 kWh of production. I expect to see 15 kWh on our lowest day (Dec 21).

What is your roof angle? That is a pretty extreme difference - we have half our solar roof on our north-facing side, and our average expected production at the solstices is 31.1 vs 11.9, and our best within a week has been 47.6 vs 17.7, so in both cases a ratio of somewhere between 2.5:1 and 3:1. Roof pitch is 34° and roof orientation is 7°/187°. (And, DC is north of Sacramento, which I note because of your NorCal location, so sun angle is pretty similar.)

Our north-facing PV definitely produces far less in the winter - about 70% of its annual production is in those 5 months near the summer solstice - but it still does contribute some throughout the year.

In any case, it certainly illustrates how solar production estimates can be very difficult as so many factors can affect a specific project.

 

[jboy210]

What since inverter(s) do you have. YOu cannot get more than their output, no matter how many tiles you have

2 inverters. 8 and 4 kW. 8 kW is on south-facing, 4kW is rest.