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Old 22-07-2018, 01:35   #1
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Same model panels - different output?

I recently purchased two 110W panels, flexible, fiberglass-backed, 7-layer, ETFE-faced. Each panel is hooked up to its own Victron SmartSolar 75/15 controller, and directly to the house bank via identical 4mm cabling.

Problem is, one panel averages 90W during the day, and the other is averaging 70W. This is now over two weeks, with the boat moving around in all orientations during that time. in fact, even on days when the "problem" panel spent longer facing the sun, the other panel still puts in better numbers. Neither is shaded and both are attached to the same bimini, in the same manner.

Is this type of asymmetry par for the course, or should the panels be within a few watts of each other?

Thanks for all advice!
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Old 22-07-2018, 02:31   #2
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Re: Same model panels - different output?

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Originally Posted by LongRange View Post
I recently purchased two 110W panels, flexible, fiberglass-backed, 7-layer, ETFE-faced. Each panel is hooked up to its own Victron SmartSolar 75/15 controller, and directly to the house bank via identical 4mm cabling.

Problem is, one panel averages 90W during the day, and the other is averaging 70W. This is now over two weeks, with the boat moving around in all orientations during that time. in fact, even on days when the "problem" panel spent longer facing the sun, the other panel still puts in better numbers. Neither is shaded and both are attached to the same bimini, in the same manner.

Is this type of asymmetry par for the course, or should the panels be within a few watts of each other?

Thanks for all advice!
this could happen, there is a wide tolerance range in the cell production. Usualy branded panels ate tested and sorted in different classes and then sold for different prises, so there are (bigger house installation-) panels looking the same, with the same cells etc. from 290Wp...360W, just different labels and prises for the selection.

Other manufacturers do not select, but just assure a minimum power output test that the panels must pass. It is cheaper for mass production to keep the process simple. Usualy they have 2 to 5 years warranty, while the selected (glas panels) have up to 20 years / 80% of the nominal current.

Flex panels normaly do not have such a long life expectance and are seldom pre-selected.
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Old 22-07-2018, 04:51   #3
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Re: Same model panels - different output?

If the controllers are regulating the power contribution from the panels will be different. This is likely to be the cause of the problem, and if so is not an issue.

Try looking at the panel output when both controllers are in bulk mode. If the panels are in identical conditions the output of each should be very close (within a few percent). If not something is wrong.

The other test that will show you how this problem can occur is to raise the battery set points (absorption and float) by 0.1v on the underperforming panels controller. The “bad” panel should become the “best” panel.
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Old 22-07-2018, 07:19   #4
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Re: Same model panels - different output?

Quick diagnoses would be to switch controllers and see if the issue persists. If not then its the controller and if so then its likely a connection in the low panel. ( high probability its in the black box on the panel) if it is the panel and not the controller.
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Old 22-07-2018, 09:01   #5
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Re: Same model panels - different output?

Please provide some source educational materials for this novice for solar E for battery charging. I want to build 3kva solar system for off the grid, semi-tropical climate. I think this should be a lot like what is accomplished on boats, but with more panels. I would have a lockout device for shore power and enough battery for about three days of rain. Also an alternate charging system for shore power and/or generator. There are ready made packaged systems but they seem expensive. References for purchasing panels and other parts in southern California.
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Old 22-07-2018, 09:41   #6
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Re: Same model panels - different output?

Crusty you might get more responses if you started a new thread elsewhere. Highjacking this thread will only be seen by those that read this thread.

Think hard about a proper title for your thread to stir up interest and get more folks to read it.

Just a suggestion..
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Old 22-07-2018, 10:05   #7
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Re: Same model panels - different output?

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Please provide some source educational materials for this novice for solar E for battery charging. I want to build 3kva solar system for off the grid, semi-tropical climate. I think this should be a lot like what is accomplished on boats, but with more panels. I would have a lockout device for shore power and enough battery for about three days of rain. Also an alternate charging system for shore power and/or generator. There are ready made packaged systems but they seem expensive. References for purchasing panels and other parts in southern California.
shoot max a pm he is from southern cal and does residential solar .
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