[RE-wrenches] Bird droppings

Mon Jul 6 13:15:19 PDT 2015

Hey Gary,

Basically the area of the dropping will lower the current of that module (and the current of that string if this is a string inverter). The amount of current loss will be the % of the dropping area vs the area of the cell it landed on. Voltage won’t be affected by things the scale of a few bird droppings.

If this is a string inverter, theoretically if one module on the string took a hit, then every other module on the string can take a hit too and not really increase the impact, as they are all already current limited by the first module to take a hit. The current of that string will just be the same as the current from the most affected module in the string. So multiple droppings really don’t have a big additive affect.

Assume all birds drop the same size load (you’re not getting seagulls over there so you’re talking starlings, robins, barn swallows, all similar size :) once one module in a string is hit, there will not be any further impact on production until some module in the string gets 2 hits on the same cell on the same module. Cells are just a string mounted in a module frame. So you could have a module with 5 droppings on it if they were all on different cells, and it would do the same as a module with just one dropping, if they were all the same size.

At some point that above example breaks down, because the bypass diodes will start to kick in if one cell grouping gets hit too hard.

As for where on the module….untill you get to the point where bypass diodes are kicking in, I don’t think there is a difference. And at what point would the diodes kick in, you’d need to get an I-V curve tracer out and play around with paintballs or something to help quantify that J

That’s the way I understand it at least. I have not gone out with my I-V tracer and dug into this in detail. It’s just based of the core parallel vs series wiring of the typical PV source circuit. I have not seen much impact to date from bird droppings on our Solaredge installs so far (the ones I KNOW where hit by birdie bombers were so close to those that weren’t that I can’t pick them out on the monitoring portal, they just look like typical manufacturing variances [all within the +/- x% power tolerances])

With Regards,

Daniel Young, 

NABCEP Certified PV Installation ProfessionalTM: Cert #031508-90

Lead Systems Designer for:

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From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of gary easton
Sent: Monday, July 06, 2015 3:36 PM
To: RE-wrenches
Subject: [RE-wrenches] Bird droppings

I have a customer with a bit of a bird problem.   The array is ground mounted and can be easily cleaned but he is wondering what the impact of for instance droppings on one cell.   And how it adds up.   Is there a rule of thumb for this? Does it depend where the cell is located in the module?

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