New 20kW solar roof install seeing low numbers

[jboy210]

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!!

I want it to rain to clean off the dirt that has accumulated since Spring. I am very curious to see the impact of rain on the roof's performance.

 

[jboy210]

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.

A lot of our drop-off in the late fall is due to shading. Even now the shadows are creeping up the south side of the house and will be on the south-facing roof in a few weeks. I love our oak trees, but they greatly impact the solar. The effect will decrease in late December when all the leaves are gone, but by then the sun will be weak.

 

[wwu123]

Great. thank you for the data point and and inverter information. I see that they can max out and clip. I've also added the orientation of my roof if that helps people. Like everyone, I guess, that buys an expensive item, they want to make sure it is what they paid for.
View attachment 717521

With an east-west-ish configuration, you'll normally have a longer, flatter curve over the course of the day, compared to one that's all-south, even though it may look like a sharp mid-day peak in the app. The east panels will peak before noon-ish, when the west panels are still low; then the opposite in the afternoon; all leads to a flatter, lower peak at mid-day. pvoutput.org is a site that you might be able to compare the width and height of your daily production with nearby systems of comparable size.

With two 7.6kw inverters, ideally they would ideally put equal amount of east and west panels on each inverter, that way 10kw of panels will probably never peak above 7.6 mid-day even in the middle of summer, certainly not this time of year. As opposed to having one "east" inverter and one "west" inverter, where all the panels peak at the same time of day, and possibly have clipping.

 

[SVDNN]

Ok, so the ultimate question is:

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

To answer briefly...your system is on par with mine, we are getting similar production numbers for this time of year. The shape of your solar production looks appropriate...therefore, most likely your system is working as it should. Would have recommended an additional power wall or 2 to help shift your solar production thru peak times (depending on your rate plan selected). Also may be more of an issue on max generation during the summer and potential clipping due to inverters size.

It is challenging to make direct comparison of panel vs tile here with others systems. Besides other variables, tile is less efficient then panels, and your system was likely setup with the idea to maximize Pv which is why you have 1/3 facing NE. Those are in essence not working during this time of year. As others mention, look at the projections you were given as to annual production in comparison to your past history of energy used. If estimated production was less then or equal to consumption for the year, then this is the time of year you will be in negative and be "paying" for the extra...particularly with the warm days recently and your need for AC. You will make it up in the summer and earn credits to use with PGE during these "winter" months. Can also get more granular as to how production decreases during different months by playing thru the production values thru PvWatts if you want. Not going to change anything you do at this point, but may be helpful to understand and to become less worried about the expectantly "low" production numbers you are seeing.

AS to getting what you paid for...
I assume cosmetic concerns were paramount in your decision as well as the capital improvement to having a new roof installed. How much is that worth to you for your Bay Area home as opposed to just the solar power generation?

 

[charlesj]

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

But, you can get the inverter's capability for more hours of the day than with less tiles.

In essence when you see a clipped bell curve, the width in time at the clipping point gets wider, more hours of peak production.

 

[SVDNN]

Powerwall +....intergrated inverters, I think now are close to 10kW inverter size each??? If that is the case, then should be fine.
Do not know these specs for sure

 

[charlesj]

I want it to rain to clean off the dirt that has accumulated since Spring. I am very curious to see the impact of rain on the roof's performance.

Good luck.

 

[bushidosunny]

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).

great point. area under the curve is what matters. tall and skinny or fat and wide can be the same.

 

[bushidosunny]

To answer briefly...your system is on par with mine, we are getting similar production numbers for this time of year. The shape of your solar production looks appropriate...therefore, most likely your system is working as it should. Would have recommended an additional power wall or 2 to help shift your solar production thru peak times (depending on your rate plan selected). Also may be more of an issue on max generation during the summer and potential clipping due to inverters size.

It is challenging to make direct comparison of panel vs tile here with others systems. Besides other variables, tile is less efficient then panels, and your system was likely setup with the idea to maximize Pv which is why you have 1/3 facing NE. Those are in essence not working during this time of year. As others mention, look at the projections you were given as to annual production in comparison to your past history of energy used. If estimated production was less then or equal to consumption for the year, then this is the time of year you will be in negative and be "paying" for the extra...particularly with the warm days recently and your need for AC. You will make it up in the summer and earn credits to use with PGE during these "winter" months. Can also get more granular as to how production decreases during different months by playing thru the production values thru PvWatts if you want. Not going to change anything you do at this point, but may be helpful to understand and to become less worried about the expectantly "low" production numbers you are seeing.

AS to getting what you paid for...
I assume cosmetic concerns were paramount in your decision as well as the capital improvement to having a new roof installed. How much is that worth to you for your Bay Area home as opposed to just the solar power generation?

Cosmetically it really modernizes my 30 year old home. I don't have a good finished product photo but here is something.

 

[jboy210]

Cosmetically it really modernizes my 30 year old home. I don't have a good finished product photo but here is something. View attachment 717946

Look great. The black shiny roof really pops!