Why is our solar production getting cut off?

[jboy210]

Hi,

I was looking at the graphs for our SolarRoof's production and noticed that the top is getting cut off. The roof has a total rating of 12.75 kW and the South facing portion is 8 kW. Both the north and south-facing roof planes are in complete sunlight. I have verified there is no shading on any part of the roof during the period in question. Any thoughts?

Here is the graph from yesterday which was sunny from 7-ish AM on.

 

[h2ofun]

Mine will do this with clouds and other facts. It is not clipping. And ones panels NEVER EVER produce the "rated" spec.

 

[jjrandorin]

what size are the inverters?

 

[skepticcyclist]

Looking at your curve it appears you had some high cloud cover throughout the day, which is why your graph isn't smooth. High clouds will limit solar when blocking the sun, but also enhance solar when the sun is on the edge of the clouds. High clouds can also cause solar to begin sooner in the morning and end later in the evening as they can act as a mirror. At the same time since solar is very limited early morning, they can also completely block solar production during the beginning of your usual solar production if they are completely blocking the sun

 

[jboy210]

No clouds on these days after early morning. Inverters are Delta M-8 (nominal power 7680 W @ 240, max 8000W) and M-4 (nominal power 3840 W @ 240V, max 4000W).

Sounds like the consensus is this to be expected. I was expecting something a little more peaked.

 

[jjrandorin]

Im not an expert on this (not even close) but it sounds like you are not being inverter limited. I find the shape of the solar production chart somewhat interesting, but I wonder if its because its solar roof. I know in my own solar panel installation, its 8.7kW sized, and my inverters are 4.2 and 3.4, yet I have never seen higher than about 6.3kW peak production at any given time, given that my panels are facing in different directions.

Thing is, for a system that size (and I remember you have some trees) that production number looks low to me for this time of year. Low like something is not reporting. I have no shading, and am in southern cali not norcal, but on a fully sunny day right now my 8.7kW system is producing about 47kWh (Saturday april 10th,) 46 kWh (Friday April 9th).

For a system that much larger than mine to have production like that looks low to me.

 

[getakey]

I have an 11.8 kW system on east and west facing roof. Here's my production for what I think is the same day in Sacramento area. There were some scattered high light clouds during the day. Seems like you have some heavy shading in the afternoon. Not sure if that totally explains your lower production.

 

[jboy210]

I have an 11.8 kW system on east and west facing roof. Here's my production for what I think is the same day in Sacramento area. There were some scattered high light clouds during the day. Seems like you have some heavy shading in the afternoon. Not sure if that totally explains your lower production.

No shading. That was my first thought. I went out and checked at 11, 12, 1, and 2 and the roof is completely unshaded and in full sunlight.

I was expecting the graph to look similar to yours and the difference was the reason I posted this question. I am in the Livermore-Pleasanton area, so our weather is not dramatically different than yours

Also, this flattening of the curve seems fixed at the 6 kW value. It has now occurred at this same value for 5 consecutive days. It is 10:45 AM now. We will hit 6 kW by11:10 and I expect the flattening will start. I wonder if one of the strings of active SolarRoof tiles is dead or one of the shutdown (not correct name) blocks is kicking in at higher current/voltages.

 

[getakey]

I see 2 issues - the flattening and the virtually zero production after 4 pm. The lack of production after 4 is why I thought you had shading

 

[jboy210]

I see 2 issues - the flattening and the virtually zero production after 4 pm. The lack of production after 4 is why I thought you had shading

I see. Yes in the afternoon we have shading. We have trees to the West that start cutting off production after 4 or so this time of year. They are on our property, so I could get them cut. But, as we get further toward summer the sun is high enough to hit the roof even in the late afternoon. But then there is the 1,000-foot hill to West that cuts off the sun. No getting around the hill. So that shading I can understand. But, this flattening is what is bothering me.

 

[h2ofun]

I see. Yes in the afternoon we have shading. We have trees to the West that start cutting off production after 4 or so this time of year. They are on our property, so I could get them cut. But, as we get further toward summer the sun is high enough to hit the roof even in the late afternoon. But then there is the 1,000-foot hill to West that cuts off the sun. No getting around the hill. So that shading I can understand. But, this flattening is what is bothering me.

Whats wrong with the flattening? I am up in Auburn, and I see this on my setup.

 

[jboy210]

Whats wrong with the flattening? I am up in Auburn, and I see this on my setup.

To me, this implies that my system has maxed out in terms of its ability to convert sunlight to electricity. That area of the roof is listed at 8 kW and if it got to 8 kW and then flattened I would understand. However, we are flattening at 6 kW.

Perhaps I am expecting too much. Do your panel's production flatten at a constant 75-80% of their rating this time of the year?

 

[Tdriver]

Temps over 80 can affect output noticeably.

 

[h2ofun]

To me, this implies that my system has maxed out in terms of its ability to convert sunlight to electricity. That area of the roof is listed at 8 kW and if it got to 8 kW and then flattened I would understand. However, we are flattening at 6 kW.

Perhaps I am expecting too much. Do your panel's production flatten at a constant 75-80% of their rating this time of the year?

My system rated 14.7 to 15K. Most I have ever ever gotten, and not ever often, is 11.9K, and this is under perfect solar conditions

 

[jboy210]

My system rated 14.7 to 15K. Most I have ever ever gotten, and not ever often, is 11.9K, and this is under perfect solar conditions

Does the curve flatten?

 

[MorrisonHiker]

Can you tell if the M-4 inverter is working properly or if all strings are functional?

My system rated 14.7 to 15K. Most I have ever ever gotten, and not ever often, is 11.9K, and this is under perfect solar conditions

Do your panels face multiple directions? Our 20.5 kW system has panels facing four different directions. At this time of the year, the system peaks around solar noon at just over 17 kW but yesterday we had intermittent clouds and sometimes hit 22 kW.

 

[h2ofun]

Does the curve flatten?

like this?

 

[h2ofun]

Can you tell if the M-4 inverter is working properly or if all strings are functional?


Do your panels face multiple directions? Our 20.5 kW system has panels facing four different directions. At this time of the year, the system peaks around solar noon at just over 17 kW but yesterday we had intermittent clouds and sometimes hit 22 kW.

2/3 face south, 1/3 face west but only get sun in afternoon. The 2/3 gets lots of shading from neighbors trees in morning.

 

[getakey]

I have a 7.6kW inverter because my original system size was 8.8kW. I added more panels a year later, but did not upgrade the inverter. You can see my output flattens a 7.6 kW in my screenshot above. I don't think I am losing that much production with the smaller inverter.

 

[jboy210]

Temps over 80 can affect output noticeably.

Temps in the high 60s.

like this?

View attachment 653554

I would be fine with this. Look at the first post to see what ours looks like.