Our PV system's power peaks around 9 am, goes down during noon and then goes back up again around 3 pm.

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Is it a fixed array or a tracking array? Are the panels all oriented and tilted the same? Are there shading issues? Are you sure the metering is measuring production and not something else like export? Are the values in the Y-axis what you would expect for this system until it levels off?
 
d0nut said:
Is it a fixed array or a tracking array? Are the panels all oriented and tilted the same? Are there shading issues? Are you sure the metering is measuring production and not something else like export? Are the values in the Y-axis what you would expect for this system until it levels off?
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Single axis tracking. I am assuming they are. No shading issues. This is the combined output of all (18) SMA inverters. The peak in the above graph was about 800 kW.
 
The maximum power point goes down as panel temperatures are increased, but I'm not sure that would account for all of the drop at midday that you are seeing.
 
Is the tracking system axis parallel to the ground and oriented N-S? If so, the modules are pointed more toward the sun in the morning and evening than they are at noon, especially in the winter.
 
The tilt is optimized for the winter months. The noonday March sun elevation is greater than the tilt and the sun is striking the panels at less than a 90° angle.

It's not the result of Daylight-Saving Time; that's not in effect yet.
 
drcampbell said:
The tilt is optimized for the winter months. The noonday March sun elevation is greater than the tilt and the sun is striking the panels at less than a 90° angle.

It's not the result of Daylight-Saving Time; that's not in effect yet.
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It still looks like a tracking and orientation artifact to me, but without knowing your setup I can't analyze it.
 
ggunn said:
Is the tracking system axis parallel to the ground and oriented N-S? If so, the modules are pointed more toward the sun in the morning and evening than they are at noon, especially in the winter.
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I'm not sure I get this visualization. The system tracks either east-west or up down. In the first case, the axis of rotation is vertical. In the second case, the axis of rotation is horizontal and points in the east-west direction, not north-south. It would seem that this system is likely the first case. As the sun moves in its arc, the tilt is fixed, and the perpendicular orientation happens at about 0930 and 1515. These times will change with the seasons and there will be two days per year where the hump is in the middle. If the system were tilt tracking, you'd always see the peak at local solar noon, not the double hump.
 
gadfly56 said:
I'm not sure I get this visualization. The system tracks either east-west or up down. In the first case, the axis of rotation is vertical. In the second case, the axis of rotation is horizontal and points in the east-west direction, not north-south.
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In the first case, the access of rotation is not vertical. The axis is generally parallel to the panel, so with a vertical axis of rotation you'd have a 90 degree tilt at all times, which is not desirable. So the rotation axis is tilted from vertical to give the desired panel tilt when the panel has an azimuth towards the equator. And the axis is tilted from vertical in a plane that includes north-south.

Agreed on the second case. I think we can infer from the shape of the graph, though, that the OP's single axis tracking is the first case.

Cheers, Wayne
 
Speculation is not very useful without knowing the specifics of the tracking system, but a N-S tracking axis parallel to the ground and congruent with the plane of the modules might yield a production curve similar to what the OP is posting. As a boundary condition consider the case of a single column of modules on such a tracker located on a flat plane with horizon view where the sun rises and sets at due east and due west and has an elevation of 60 degrees at noon. The modules would be pointed directly at the sun at sunrise and sunset but they would be 30 degrees off axis at noon.
 
main197 said:
Thank you everyone for the input. PV is not my strong suit, so your comments help. I found some details about the tracker.

View attachment 2559753
View attachment 2559754
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That is consistent with what I was imagining. As the sun moves across the sky the insolation will be more normal to the surface of the modules when the tracker is at its extreme excursion points than it will be at the tracker's midpoint. That could explain the dip in production in the middle of the day. Compare the production curves between the winter solstice and the summer solstice; IMO the dip will be less pronounced in the summer.
 
ggunn said:
That is consistent with what I was imagining. As the sun moves across the sky the insolation will be more normal to the surface of the modules when the tracker is at its extreme excursion points than it will be at the tracker's midpoint. That could explain the dip in production in the middle of the day. Compare the production curves between the winter solstice and the summer solstice; IMO the dip will be less pronounced in the summer.
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I think the dip will be least pronounced or nonexistent in winter, the more so as latitude increases. Anywhere outside the tropics I think the dip makes sense most other times of the year, but will be most pronounced closer to the equinoxes.
 
jaggedben said:
I think the dip will be least pronounced or nonexistent in winter, the more so as latitude increases. Anywhere outside the tropics I think the dip makes sense most other times of the year, but will be most pronounced closer to the equinoxes.
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How do you figure that? The sun is the highest in the sky at noon on the summer solstice, which would be the midday when the angle of the insolation would be the closest to normal incidence to the modules.
 
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