Center row of panels

[EnergyKurt]

does a center row of panels always produce a little less power when it is between two others due to heating???

[SunEagle]

Depends. Most of the cooling comes from the air flow beneath the panel. So if that is blocked or reduced as compare to the panels on the edges you might see a minor reduction in output.

If you have micro inverters on those panels, they would be effected more than just a string inverter system.

[J.P.M.]

Hard to say for sure. Harder to measure. Provided the array is unshaded, and depending on the wind pattern across an array, and its variability, the panels that are "downwind", that is on the trailing edge of the array relative to the wind vector will have a somewhat higher temp. than the panels that are "upwind', that is on the leading edge of the array relative to the wind vector.

Depending mostly on the magnitude of the wind vector, and its variability, I've measured temp. differences over a 4 X 4 array in landscape orientation from about zero for little to no wind to about 2 to 3 deg. C. from leading to trailing edge in a 3 m/sec. wind environment.

The pattern of temp. variation of individual panel temps. seems to generally follow well established heat transfer correlations for flow over a flat plate. Unless you have the time and stamina for a lot of individual panel measurements in a very short period of time, or a way to instrument the array that is accurate and does not affect temps., see the literature with respect to flow over a flat plate, or Duffie and Beckman for further information.

Getting an average or representative panel temp., or trying to get a temp. distribution of individual panel temps. over an array is made most difficult by a certain lack of knowledge of how the wind vector and its variability is distributed over an array, and also how that distribution can affect temps., neither of those things being well understood due to the complexities of how flow patterns are affected by panel shapes, array tilts, under panel clearances and several ,other variables.

[bcroe]

does a center row of panels always produce a little less power when it is between two others due to heating???

The difference is going to be VERY small. However, I'm listing it anyway as reason #34 to prefer a ground mount. Bruce Roe

[littleharbor]

Oh yeah, I remember the list. can you post a link to it for others? Or keywords to search with.

[bcroe]

Oh yeah, I remember the list. can you post a link to it for others? Or keywords to search with.

I put in my PROFILE, BIOGRAPHY which I hope others can access.

[EnergyKurt]

Yes, it is very little... approx 4 to 10 watts difference on average..but if you look at the SolarEdge data it shows up over time. The week and month view makes it more visible.
it shows up even less spring, fall and winter which let me to believe it was all about temperature.


picture is a current week view
see pic below

[J.P.M.]

Yes, it is very little... approx 4 to 10 watts difference on average..but if you look at the SolarEdge data it shows up over time. The week and month view makes it more visible.
it shows up even less spring, fall and winter which let me to believe it was all about temperature.


picture is a current week view
see pic below

Note that the output difference is greater and looking more consistent from left to right. What's the orientation in that picture. Which way is north ?

[EnergyKurt]

North is about 2 oclock
Those panels are facing south/ southeast and the roof line shades the morning sun...
higher values to the left and little lower to the right is expected

[J.P.M.]

North is about 2 oclock
Those panels are facing south/ southeast and the roof line shades the morning sun...
higher values to the left and little lower to the right is expected

Thank you. That shading may be responsible for some of the east deficit.

Another question: What's the clearance between the panels and the roof ? If it's not much clearance, that may help explain some of the middle row deficit.

[EnergyKurt]

Sorry didn't see the question... panels are approx 5" off the roof..
black panels and black roof
roof is 12/12 so 45 degree

[J.P.M.]

Sorry didn't see the question... panels are approx 5" off the roof..
black panels and black roof
roof is 12/12 so 45 degree

Thank you.
Clearance ain't bad, but more of the cooling will still be from the top surface of the panels, if for no other reason that there will be less radiation heat transfer between the panels and the roof deck than between the panels and the sky because the deck under the array will be at a higher temp. than the effective radiant sky temp.

I'd SWAG that if the output energy profile you show is fairly representative, wind more from the west or southwest may be more common as the temps of leading edge ("upstream") panels will be lower, and the corresponding individual panel output lower as the panel temps. get higher farther from the upstream edge of the array. I've measured similar temp. patterns on my array more than 100 + times with different wind vector directions.

Also, panels in the middle row will not have an edge exposed to free air flow. That may serve to decrease convective heat transfer and increase panel temps. of the middle row panels a bit with the result that individual panel efficiency and thus output is lowered some.

There's more than one wind regime at work here, maybe several.