quick shading question

[Dforster67]

i have a few tall trees off to the east of my panels about 200 feet away in a fence row. they only provide shade until about 10 or 10:30am. so my question is are they causing shade issues for the panels?

If they were shading the panels until noon I'd definitely just cut them down now. but maybe the sun isn't high enough to provide more energy to the panels anyway at 10am.

a few data points for comparison:

NE Oklahoma
south facing ground fixed tilt (30 degrees)
5.3kw of panels that have been producing up to 5kw mid-day already this spring.
currently producing 1.1 kw at 9:23am
about 1/3 of the panels seem to be partially shaded by the 2-3 trees (at 9:30 am).

mid-installation photo shows the trees off to the left. it doesn't look like it, but most of the shading is caused by the 2-3 smaller trees to the south (circled) and just a few branches on the big tree.

 

[snoobler]

Shading is bad and can devastate production. In a typical panel, shade a single cell, and you cut output by 33%.

It's hard to say what your situation warrants. If you have a means of plotting the production of the array, you can likely estimate the impact of the shading.

Using our arrays on a comparative basis, you're producing 20% of rated at 9:23am.

Yesterday, I was producing 20% at 6:42am:



We are likely pretty close in latitude, and my array is at 29°. One key difference is my array is oriented East of South by about 15°, assuming you're due South. This shifts my peak production to about 11:20am vs. noon-ish, so I would estimate YOUR array would produce 20% of its rated power closer to 7:30am CST or 8:30am CDT.

At 7:42am (1 hour after the above), my array is pushing 50% rated.

Spitballing a SWAG, your shading might be costing you 1.5-2kWh/day.

Personally, I would cut down the trees just on principle.

 

[Dforster67]

I can plot the output with optics on the skybox. But my production is not going to be maxed out because I am not selling and don’t have my batteries yet. I just happened to catch it this morning when we were using 1.5kw and only producing 1kw. We are normally idling around 500 watts so I am wasting a lot right now anyway, unfortunately.

Thanks for the info! Very useful. I didn’t realize shading was that detrimental to production.
I was probably gonna cut them down someday anyway. They are just ugly old elm trees. Will make good firewood this winter.

 

[GXMnow]

I had a similar, but opposite issue. I have palm trees in my yard. My system was installed in summer and I didn't see a problem, but as winter rolled around, I noticed production dropping early. I walk outside and see the shadow hitting 4 panels out of my 16. I have microinverters, so it was only hurting the panels with shade on them. If it was a series string, like your Skybox, it would cut the power a lot more. Shadows are a killer for solar. Can you turn your ground mount array, or is the south facing angle fixed? If it is clear to the west, turning the array a bit would reduce the morning production a bit, but it would produce more later in the day. As it went further into winter, and the trees grow like weeds, it got to where it was knocking out up to 8 panels, half of my whole array, so I did end up cutting down the 3 of my palm trees close to my house. I still have 3 more, and one of them has grown enough to start giving me a little evening shade again. But as we move more into summer, the problem goes away again. The first 3 I cut down were costing me as much as 5 kwh a day in the winter. Even at that for 100 days of the year, that is only $115 a year at 23 cents a kwh. It cost about $2,000 to have them cut down and hauled away. So 17 YEARS to pay off the cost of tree removal. Hmmm. My array is flat on my roof, no option to turn it.

 

[snoobler]

This video shows how full-cell shading affects typical panels:

The full cell shading has a substantial effect. Shading from tree branches may not be as severe as the full cell coverage with the sign, but the single "power line" cut the panel's output by 4%. I expect the affect of tree branches will cut quite a bit more than that.

If you're curious, consider running a significant load to generate a morning power plot to show peak production (your loads will need to always be higher than your PV production) during that period. You'll be able to see where the system transitions to unshaded operation and can estimate your losses.

 

[snoobler]

I had a similar, but opposite issue. I have palm trees in my yard. My system was installed in summer and I didn't see a problem, but as winter rolled around, I noticed production dropping early. I walk outside and see the shadow hitting 4 panels out of my 16. I have microinverters, so it was only hurting the panels with shade on them. If it was a series string, like your Skybox, it would cut the power a lot more. Shadows are a killer for solar. Can you turn your ground mount array, or is the south facing angle fixed? If it is clear to the west, turning the array a bit would reduce the morning production a bit, but it would produce more later in the day.

I was going to suggest this based on my own array's configuration, (we tend to have cloudy afternoons, so we favor morning production), but it looked to me as though that sucker was embedded in concrete.

 

[Alphacarina]

I would be stocking up on firewood for the fall & winter about now . . . . It can dry out over the summer

Don

 

[Dforster67]

I was going to suggest this based on my own array's configuration, (we tend to have cloudy afternoons, so we favor morning production), but it looked to me as though that sucker was embedded in concrete.

Exactly. I used the unirac gft. Those suckers are 6’ into the ground with 4 yards or concrete footing around them ?. Panels are so cheap compared with fancy tracking mount options I just figured I could add a few more arrays over the years if I need to. I’ve got 70 ares of pasture to add on!

 

[Dforster67]

Well I managed to clear out most of that row of trees. I left one large tree for now. I’ll try to see what it’s doing to energy production as I get done more history

But I did notice about twice the production the next day during the 8 am hour. Well twice the peak power anyway since I don’t have a steady load yet I can’t really go by production.